- A -
absorption.
A process in which liquid molecules are taken up by a liquid or solid and distributed throughout the body of that liquid or solid. Compare with adsorption..
accelerated corrosion test.
Method designed to approximate, in a short time, the deteriorating effect under normal long-term service conditions.
acid.
A chemical substance that yields hydrogen ions (H) when dissolved in water. Compare with base..
acid embrittlement.
A form of hydrogen embrittlement that may be induced in some metals by acid. acid rain.
Atmospheric precipitation with a pH below 3.6 to 5.7. Burning of fossil fuels for heat and
power is the major factor in the generation of oxides of nitrogen and sulfur, which are converted into nitric and sulfuric acids washed down in the rain. See also atmospheric corrosion.
acicular ferrite.
A highly substructured non-equiaxed ferrite formed upon continuous cooling by a mixed
diffusion and shear mode of transformation that begins at a temperature slightly higher than the transformation temperature range for upper bainite. It is distinguished from
bainite in that it has a limited amount of carbon available thus, there is only a small amount of carbide present.
acrylic.
Resin polymerized from acrylic acid, methacrylic acid, eaters of these acids, or
acrylonitrile.
activation.
The changing of a passive surface of a metal to a chemically active state. Contrast with passivation..
active
A state in which a metal tends to corrode; referring to the negative direction of electrode potential (opposite of passive or noble).
active metal
A metal ready to corrode, or being corroded active potential.
The potential of a corroding material.
activity.
A measure of the chemical potential of a substance, where chemical potential is not equal to concentration, that allows mathematical relations equivalent to those for ideal systems to be used to correlate changes in an experimentally measured quantity with changes in chemical potential.
+
activity (ion).
The ion concentration corrected for deviations from ideal behavior. Concentration multiplied by activity coefficient. activity coefficient. A characteristic of a quantity expressing the deviation of a solution from ideal thermodynamic behavior; often used in connection with electrolytes.
addition agent.
A substance added to a solution for the purpose of altering or controlling a process. Examples include wetting agents in acid pickles, brighteners or antipitting agents in plating solutions, and inhibitors.
additive
A substance added in a small amount, usually to a fluid, for a special purpose, such as to reduce friction, corrosion, etc.
adsorption.
The surface retention of solid, liquid, or gas molecules, atoms, or ions by a solid or liquid. Compare with absorption..
aeration.
(1) Exposing to the action of air. (2) Causing air to bubble through. (3) Introducing air into a solution by spraying, stirring, or a similar method. (4) Supplying or infusing with air, as in sand or soil.
aeration Cell
An oxygen concentration cell; an electrolytic cell resulting from differences in dissolved
oxygen at two points. Also see differential aeration cell..
age hardening.
Hardening by aging, usually after rapid cooling or cold working.
aging.
A change in the properties of certain metals and alloys that occurs at ambient or moderately elevated temperatures after hot working or a heat treatment (quench aging in ferrous alloys, natural or artificial aging in ferrous and nonferrous alloys) or after a cold-working operation (strain aging). The change in properties is often, but not always, due to a phase change (precipitation), but never involves a change in chemical composition of the metal or alloy. See also age hardening, artificial aging, natural aging, averaging, precipitation hardening, precipitation heat treatment, quench aging, and strain
aging..
alclad.
Composite wrought product comprised of an aluminum alloy core having on one or both surfaces a metallurgically bonded aluminum or aluminum alloy coating that is anodic to the core and thus electrochemically protects the core against corrosion.
alkali metal.
A metal in group lA of the periodic system – namely, lithium, sodium, potassium,
rubidium, cesium, and francium. They form strongly alkaline hydroxides, hence the name.
alkaline.
(1) Having properties of an alkali. (2) Having a pH greater than 7.
alkaline cleaner.
A material blended from alkali hydroxides and such alkaline salts as borates, carbonates, phosphates, or silicates. The cleaning action may be enhanced by the addition of surface-active agents and special solvents.
alkyd.
Resin used in coatings. Reaction products of polyhydric alcohols and polybasic acids.
alkylation.
(1) A chemical process in which an alkyl radical is introduced into an organic compound by substitution or addition. (2) A refinery process for chemically combining isoparaffin with olefin hydrocarbons.
alligatoring.
(1) Pronounced wide cracking over the entire surface of a coating having the appearance of alligator hide. (2) The longitudinal splitting of flat slabs in a plane parallel to the rolled
surface. Also called fish-mouthing.
alloy plating.
The codeposition of two or more metallic elements.
alpha ferrite.
See ferrite..
alpha iron.
The body-centered cubic form of pure iron, stable below 910 oC (l670 oF). alternate-immersion test.
A corrosion test in which the specimens are intermittently exposed to a liquid medium at
definite time intervals.
aluminizing.
Forming of an aluminum or aluminum alloy coating on a metal by hot dipping, hot spraying, or diffusion. amalgam.
An alloy of mercury with one or more other metals.
ammeter.
An instrument for measuring the magnitude of electric current flow.
amorphous solid.
A rigid material whose structure lacks crystalline periodicity; that is, the pattern of its constituent atoms or molecules does not repeat periodically in three dimensions. See also
metallic glass..
amphoteric.
A term applied to oxides and hydroxides which can act basic toward strong acids and acidic toward strong alkalis. Substances which can dissociate electrolytically to produce hydrogen or hydroxyl ions according to conditions.
anchorite.
A zinc-iron phosphate coating for iron and steel. anaerobic
In the absence of air or unreacted or free oxygen.
anion
An ion or radical which is attracted to the anode because of the negative charge. See also cation and ion.
annealing.
A generic term denoting a treatment. consisting of heating to and holding at a suitable temperature, followed by cooling at a suitable rate, used primarily to soften metallic materials, but also to simultaneously produce desired changes in other properties or in microstructure. The purpose of' such changes may be. but is not confined to. improvement of machinability, facilitation of cold work, improvement of mechanical or electrical properties, and/or increase in stability of dimensions. When the term is used by itself, full annealing is implied. When applied only for the relief of stress, the process is properly called stress relieving or stress-relief annealing.
anode
The electrode at which oxidation or corrosion of some component occurs (opposite of cathode). Electrons flow away from the anode in the external circuit.
anode corrosion.
The dissolution of a metal acting as an anode.
anode corrosion efficiency
Ratio of actual to theoretical corrosion based on the total current flow calculated by Faraday’s law from the quantity of electricity that has passed.
anode effect.
The effect produced by polarization of the anode in electrolysis. It is characterized by a
sudden increase in voltage and a corresponding decrease in amperage due to the anode becoming virtually separated from the electrolyte by a gas film.
anode efficiency.
Current efficiency of the anode..
anode film.
(1) The portion of solution in immediate contact with the anode, especially if the concentration gradient is steep. (2) The outer layer of the anode itself.
anodic cleaning.
Electrolytic cleaning in which the work is the anode. Also called reverse-current cleaning.
anodic coating.
A film on a metal surface resulting from an electrolytic treatment at the anode.. anodic inhibitor
A chemical substance or combination of substances that prevent or reduce the rate of the anodic or oxidation reaction by a physical, physico-chemical or chemical action.
anodic polarization
The change in the initial anode potential resulting from current flow effects at or near the anode surface. Potential becomes mode noble (more positive) because of anodic polarization.
anodic potential
An appreciable reduction in corrosion by making a metal an anode and maintaining this
highly polarized condition with very little current flow.
anodic protection
A technique to reduce corrosion of a metal surface under some conditions by passing sufficient to it to cause its electrode potential to enter and remain in the passive region; imposing an external electrical potential to protect a metal from corrosive attack.
(Applicable only to metals that show active-passive behavior.) Contrast with cathodic
protection..
anodic reaction.
Electrode reaction equivalent to a transfer of positive charge from the electronic to the ionic conductor. An anodic reaction is an oxidation process. An example common in
corrosion is:
Me -> Me(+n) + n(e-).
anodizing.
Forming a conversion coating on a metal surface by anodic oxidation; most frequently
applied to aluminum.
anolyte
The electrolyte adjacent to the anode in an electrolytic cell.
anti-fouling
Intended to prevent fouling of under-water structures, such as the bottoms of ships; refers
to the prevention of marine organism's attachment or growth on a submerged metal surface, generally through chemical toxicity caused by the composition of the metal or
coating layer.
antipitting agent.
An addition agent for electroplating solutions to prevent the formation of pits or large
pores in the electrodeposit.
aqueous.
Pertaining to water; an aqueous solution is made by using water as a solvent.
artificial aging.
Aging above room temperature. See also aging. Compare with natural aging..
atmospheric corrosion.
The gradual degradation or alteration of a material by contact with substances present in the atmosphere, such as oxygen. carbon dioxide, water vapor, and sulfur and chlorine
compounds.
austenitic
The name given to the face-centered cubic crystal structure (FCC) of ferrous metals.
Ordinary iron and steel has this structure at elevated temperatures; also certain stainless steels (300 series) have this structure at room temperature.
austenite.
A solid solution of one or more elements in face-centered cubic iron. Unless otherwise designated (such as nickel austenite), the solute is generally assumed to be carbon.
austenitizing.
Forming austenite by heating a ferrous alloy into the transformation range (partial austenitizing) or above the transformation range (complete austenitizing). When used without qualification, the term implies complete austenitizing.
auxiliary anode.
In electroplating, a supplementary anode positioned so as to raise the current density on a
certain area of the cathode and thus obtain better distribution of plating.
auxiliary electrode
An electrode commonly used in polarization studies to pass current to or from a test
electrode, usually made of noncorroding material.
- B -
backfill
Material placed in a drilled hole to fill space around anodes, vent pipe, and buried components of a cathodic protection system.
bainite
A metastable aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures below the pearlite range but above M the martensite start temperature. Bainite formed in the upper part of the bainite transformation range has a feathery appearance; bainite formed in the lower part of the range has an acicular appearance resembling that of tempered martensite. banded structure
A segregated structure consisting of alternating nearly parallel bands of different composition, typically aligned in the direction of primary hot working.
base
A chemical substance that yields hydroxyl ions (OH ) when dissolved in water. Compare with acid.
base metal
(1) The metal present in the largest proportion in an alloy; brass, for example, is a copper-base alloy. (2) An active metal that readily oxidizes, or that dissolves to form ions. (3) The metal to be brazed, cut, soldered, or welded. (4) After welding, that part of the metal which was not melted. beach marks
Macroscopic progression marks on a fatigue fracture or stress-corrosion cracking surface that indicate successive positions of the advancing crack front. The classic appearance is of irregular elliptical or semielliptical rings, radiating outward from one or more origins. Beach marks (also known as clamshell marks or arrest marks) are typically found on service fractures where the part is loaded randomly, intermittently, or with periodic variations in mean stress or alternating stress. See also striation. biaxial stress
See principal stress (normal). bimetallic corrosion
(Galvanic Corrosion) Corrosion resulting from dissimilar metal contact. biological corrosion
Deterioration of metals as a result of the metabolic activity of microorganisms. bipolar electrode
An electrode in an electrolytic cell that is not mechanically connected to the power supply, but is so placed in the electrolyte, between the anode and cathode, that the part nearer the anode becomes cathodic and the part nearer the cathode becomes anodic. Also called intermediate electrode. bituminous coating
Coal tar or asphalt-based coating.
black liquor
The liquid material remaining from pulpwood cooking in the soda or sulfate paper-making process. black oxide
A black finish on a metal produced by immersing it in hot oxidizing salts or salt solutions. blister
A raised area, often dome shaped, resulting from (1) loss of adhesion between a coating or deposit and the base metal or (2) delamination under the pressure of expanding gas trapped in a metal in a near-subsurface zone. Very small blisters may be called pinhead blisters or pepper blisters. blow down
(1) Injection of air or water under high pressure through a tube to the anode area for the purpose of purging the annular space and possibly correcting high resistance caused by gas blocking. (2) In connection with boilers or cooling towers, the process of discharging a significant portion of the aqueous solution in order to remove accumulated salts, deposits, and other impurities. blue brittleness
Brittleness exhibited by some steels after being heated to a temperature within the range of about 200 to 370 oC (400 to 700 oF), particularly if the steel is worked at the elevated temperature.
blushing
Whitening and loss of gloss of a usually organic coating caused by moisture. Also called blooming.
brackish water
(1) Water having salinity values ranging from approximately 0.5 to l7 parts per thousand. (2) Water having less salt than seawater, but undrinkable.
breakdown potential
The least noble potential where pitting or crevice corrosion, or both, will initiate and propagate.
brightener
An agent or combination of agents added to an electroplating bath to produce a smooth, lustrous deposit. brine
Seawater containing a higher concentration of dissolved salt than that of the ordinary ocean. brittle fracture
Separation of a solid accompanied by little or no macroscopic plastic deformation. Typically, brittle fracture occurs by rapid crack propagation with less expenditure of energy than for ductile fracture. burning
(1) Permanently damaging a metal or alloy by heating to cause either incipient melting or intergranular oxidation. See also over-heating. (2) In grinding, getting the work hot enough to cause discoloration or to change the microstructure by tempering or hardening.
- C -
calcareous coating or deposit.
A layer consisting of a mixture of calcium carbonate and magnesium hydroxide deposited on surfaces being cathodically protected because of the increased pH adjacent to the protected surface. calomel electrode.
An electrode widely used as a reference electrode of known potential in electrometric measurement of acidity and alkalinity, corrosion studies, voltammetry, and measurement of the potentials of other electrodes. See also electrode potential, reference electrode, and saturated calomel electrode. calorizing.
Imparting resistance to oxidation to an iron or steel surface by heating in aluminum powder at 800 to 1000 oC (1470 to 1830 oF). carbonitriding.
A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and, by diffusion, create a concentration gradient. The process is completed by cooling at a rate that produces the desired properties in the workpiece. carburizing.
The absorption of carbon atoms by a metal at high temperatures; it may remain dissolved, or form metal carbides; Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperature or by cooling to room temperature then reaustenitizing and quenching. Carburization
The absorption of carbon into a metal surface; may or may not be desirable. case hardening.
A generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two and, by diffusion, create a concentration gradient. The outer portion, or case, is made substantially harder than the inner portion, or core. The processes commonly used are carburizing and quench hardening; cyaniding: nitrifying; and carbonitriding. The use of the applicable specific process name is preferred. CASS test.
See copper-accelerated salt-spray test. cathode.
The electrode of an electrolytic cell at which reduction is the principal reaction. (Electrons How toward the cathode in the external circuit.) Typical cathodic processes
are cation' taking up electrons and being discharged, oxygen being reduced. and the reduction of an element or group of elements from a high Cl a lower valence state. Contrast with anode. cathode efficiency.
Current efficiency at the cathode. cathode film.
The portion of solution in immediate contact with the cathode during electrolysis. cathodic cleaning.
Electrolytic cleaning in which the work is the cathode. cathodic corrosion.
Corrosion resulting from a cathodic condition of a structure usually caused by the reaction of an amphoteric metal with the alkaline products of electrolysis. cathodic disbondment.
The destruction of adhesion between a coating and its substrate by products of a cathodic reaction. cathodic inhibitor.
A chemical substance or mixture that prevents or reduces the rate of the cathodic or reduction reaction by physical, physico-chemical or chemical action. cathodic pickling.
Electrolytic pickling in which the work is the cathode. cathodic polarization.
Polarization of the cathode; change of the electrode potential in the active (negative) direction due to current flow; a reduction from the initial potential resulting from current flow effects at or near the cathode surface. Potential becomes more active (negative) because of cathodic polarization. See also polarization. cathodic protection.
(1) Reduction of corrosion rate by shifting the corrosion potential of the electrode toward a less oxidizing potential by applying an external electromotive force. (2) Partial or complete protection of a metal from corrosion by making it a cathode, using either a galvanic or an impressed current. Contrast with anodic protection. cathodic reaction.
Electrode reaction equivalent to a transfer of negative charge from the electronic to the ionic conductor. A cathodic reaction is a reduction process. An example common in corrosion is: Ox + ne s Red. catholyte.
The electrolyte adjacent to the cathode of an electrolytic cell. cation.
A positively charged ion that migrates through the electrolyte toward the cathode under the influence of a potential gradient. See also anion and ion. caustic.
(1) Burning or corrosive. (2) A hydroxide of a light metal, such as sodium hydroxide or potassium hydroxide. caustic dip.
A strongly alkaline solution into which metal is immersed for etching. for neutralizing
acid, or for removing organic materials such as greases or paints. caustic embrittlement.
An obsolete historical term denoting a form of stress-corrosion cracking most frequently encountered in carbon steels or iron-chromium-nickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 200 to 250 oC (400 to 480 oF). cavitation.
The formation and instantaneous collapse of innumerable tiny voids or cavities within a liquid subjected to rapid and intense pressure changes. Cavitation produced by ultrasonic radiation is sometimes used to effect violent localized agitation. Cavitation caused by severe turbulent flow often leads to cavitation damage. cavitation corrosion.
A process involving conjoint corrosion and cavitation. cavitation damage.
The degradation of a solid body resulting from its exposure to cavitation. This may include loss of material, surface deformation, or changes in properties or appearance. cavitation-erosion.
Progressive loss of original material from a solid surface due to continuing exposure to cavitation. cell.
Electrochemical system consisting of an anode and a cathode immersed in an electrolyte. The anode and cathode may be separate metals or dissimilar areas on the same metal. The cell includes the external circuit, which permits the flow of electrons from the anode toward the cathode. See also electrochemical cell. Cementation Coating
A coating developed on a metal surface by a high temperature diffusion process (as carburization, calorizing, or chromizing). cementite.
A compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition will be altered by the presence of manganese and other carbide-forming elements. chalking.
The development of loose removable powder at the surface of an organic coating usually caused by weathering. checking.
The development of slight breaks in a coating that do not penetrate to the underlying surface. checks.
Numerous, very fine cracks in a coating or at the surface of a metal part. Checks may appear during processing or during service and are most often associated with thermal treatment or thermal cycling. Also called check marks. checking, or heat checks. chelate.
(1) A molecular structure in which a heterocyclic ring can he formed by the unshared electrons of neighboring atoms. (2) A coordination compound in which a heterocyclic ring is formed by a metal bound to two atoms of the associated ligand. See also complexation. chelating agent.
(1) An organic compound in which atoms form more than one coordinate bond with metals in solution. (2) A substance used in metal finishing to control or eliminate certain metallic ions present in undesirable quantities. chelation.
A chemical process involving formation of a heterocyclic ring compound that contains at least one metal cation or hydrogen ion in the ring. chemical conversion coating.
A protective or decorative nonmetallic coating produced in silo by chemical reaction of a metal with a chosen environment. It is often used to prepare the surface prior to the application of an organic coating. chemical potential.
In a thermodynamic system of several constituents, the rate of change of the Gibbs function of the system with respect to the change in the number of moles of a particular constituent. chemical vapor deposition.
A coating process, similar to gas carburizing and carbonitriding, whereby a reactant atmosphere gas is fed into a processing chamber where it decomposes at the surface of the workpiece, liberating one material for either absorption by, or accumulation on the workpiece. A second material is liberated in gas form and is removed from the processing chamber, along with excess atmosphere gas. chemisorption.
The binding of an adsorbate to the surface of a solid by forces whose energy levels approximate those of a chemical bond. Contrast with physisorption. chevron pattern.
A fractographic pattern of radial marks (shear ledges) that look like nested letters \"V\"; sometimes called a herringbone pattern. Chevron patterns are typically found on brittle fracture surfaces in parts whose widths are considerably greater than their thicknesses. The points of the chevrons can be traced back to the fracture origin. chromadizing.
Improving paint adhesion on aluminum or aluminum alloys, mainly aircraft skins, by treatment with a solution of' chromic acid. Also called chromodizing or chromatizing. Not to be confused with chromating or chromizing. chromate treatment.
A treatment of metal in a solution of a hexavalent chromium compound to produce a conversion coating consisting of trivalent and hexavalent chromium compounds. chromating.
Performing a chromate treatment . chrome pickle.
(1) Producing a chromate conversion coating on magnesium for temporary protection
or for a paint base. (2) The solution that produces the conversion coating. chromizing.
A surface treatment at elevated temperature, generally carried out in pack, vapor, or salt bath, in which an alloy is formed by the inward diffusion of chromium into the base metal. clad metal.
A composite metal containing, two or more layers that have been bonded together. The bonding may have been accomplished by co-rolling, co-extrusion, welding, diffusion bonding, casting, heavy chemical deposition, heavy electroplating, or explosive cladding. cleavage.
Splitting (fracture) of a crystal on a crystallographic plane of' low index. cleavage fracture.
A fracture, usually of' polycrystalline metal, in which most of the grains have failed by cleavage, resulting in bright reflecting facets. It is associated with low-energy brittle fracture. cold cracking.
A type of weld cracking that usually occurs below 203 oC (400 \"F). Cracking may occur during or after cooling to room temperature, sometimes with a considerable time delay. Three factors combine to produce cold cracks: stress (for example, from thermal expansion and contraction). hydrogen (from hydrogen-containing welding consumables), and a susceptible micro.structure (plate martensite is most susceptible to cracking, ferritic and bainitic structures least susceptible). See also hot cracking, lamellar tearing and stress-relief cracking. cold working.
Deforming metal plastically under conditions of temperature and strain rote that induce strain hardening. Usually, hut not necessarily, conducted at room temperature. Contrast with hot working. combined carbon.
The part of the total carbon in steel or cast iron that is present as other than free carbon. complexation.
The formation of complex chemical species by the coordination of groups of atoms termed ligands to a central ion, commonly a metal ion. Generally, the ligand coordinates by providing a pair of electrons that forms an ionic or covalent bond to the central ion. See also chelate, coordination compound, and ligand. compressive.
Pertaining to forces on a body or part of a body that tend to crush or compress the body.
compressive strength.
The maximum compressive stress a material is capable of developing. With a brittle material that fails in compression by fracturing, the compressive strength has a definite value. In the case of ductile, malleable, or semiviscous materials (which do not fail in compression by a shattering fracture), the value obtained for compressive
strength is an arbitrary value dependent on the degree of distortion that is regarded as effective failure of the material. compressive stress.
A stress that causes an elastic body to deform (shorten) in the direction of the applied load. Contrast with tensile stress. concentration cell.
An electrolytic cell, the electromotive force of which is caused by a difference in concentration of some component in the electrolyte. This difference leads to the formation of discrete cathode and anode regions. concentration polarization.
That portion of the polarization of a cell produced by concentration changes resulting from passage of' current through the electrolyte. conductivity.
The ratio of the electric current density to the electric field in a material. Also called electrical conductivity or specific conductance. contact corrosion.
A term primarily used in Europe to describe galvanic corrosion between dissimilar metals.
contact plating.
A metal plating process wherein the plating current is provided by galvanic action between the work metal and a second metal, without the use of an external source of current.
contact potential.
The potential difference at the junction of two dissimilar substances. continuity bond.
A metallic connection that provides electrical continuity between metal structures. conversion coating.
A coating consisting of' a compound of the surface metal, produced by chemical or electrochemical treatments of the metal. Examples include chromate coatings on zinc, cadmium, magnesium, and aluminum and oxide and phosphate coatings on steel. See also chromate treatment and phosphating. coordination compound.
A compound with a central atom or ion bound to a group of ions or molecules surrounding it. Also called coordination complex. See also chelate, complexation, and ligand.
copper-accelerated salt-spray (CASS) test.
An accelerated corrosion test for some electrodeposits for anodic coatings on aluminum. corrodkote test.
An accelerated corrosion test for electrodeposits. corrosion.
The chemical or electrochemical reaction between a material, usually a metal, and its environment that produces a deterioration of the material and its properties. corrosion effect.
A change in any part of the corrosion system caused by corrosion. corrosion embrittlement.
The severe loss of ductility of a metal resulting from corrosive attack, usually inter,granular and often not visually apparent. corrosion-erosion.
Corrosion which is increased because of the abrasive action of a moving stream; the presence of suspended particles greatly accelerates abrasive action.See erosion-corrosion. corrosion fatigue.
The process in which a metal fractures prematurely under conditions of simultaneous corrosion and repeated cyclic loading at lower stress levels or fewer cycles than would be required in the absence of the corrosive environment. Corrosion Fatigue Limit
The maximum cyclic stress value that a metal can with stand for a specified number of cycles or length of time in a given corrosive environment. See corrosion fatigue strength
corrosion fatigue strength.
The maximum repeated stress that can he endured by a metal without failure under definite conditions of corrosion and fatigue and for a specific number of stress cycles and a specified period of time. corrosion inhibitor. See inhibitor.
corrosion potential (Ecorr).
The potential of a corroding surface in an electrolyte, relative to a reference electrode. Also called rest potential, open circuit potential, or freely corroding potential. corrosion product.
Substance formed as a result of corrosion. corrosion protection.
Modification of a corrosion system so that corrosion damage is mitigated. corrosion rate.
Corrosion effect on a metal per unit of time. The type of corrosion rate used depends on the technical .system and on the type of corrosion effect. Thus, corrosion rate may be expressed as an increase in corrosion depth per unit of time (penetration rate, for example, mils/yr.) or the mass of metal turned into corrosion products per unit area of surface per unit of time (weight loss, for example, g/m-/yr.). The corrosion effect may vary with time and may not be the same at all points of the corroding surface. Therefore. reports of corrosion rates should be accompanied by information on the type, time dependency, and location of the corrosion effect. corrosion resistance.
Ability of a metal to withstand corrosion in a given corrosion system. corrosion system.
System consisting of one or more metals and all parts of the environment that influence corrosion. corrosivity.
Tendency of an environment to cause corrosion in a given corrosion system. counter electrode. See auxiliary electrode . couple.
A cell developed in an electrolyte resulting from electrical contact between two dissimilar metals. See galvanic corrosion. covering power.
The ability of a solution to give satisfactory plating at very low current densities. a condition that exists in recesses and pits. This term suggests an ability to cover, but not necessarily to build up, a uniform coating, whereas throwing power suggests the ability to obtain a coating of uniform thickness of an irregularly shaped object. cracking (of coating).
Breaks in a coating that extend through to the underlying surface. crazing.
A network of checks or cracks appearing on the surface. creep.
Time-dependent strain occurring under stress. The creep strain occurring at a diminishing rate is called primary creep; that occurring at a minimum and almost constant rate, secondary creep; and that occurring at an accelerating rate, tertiary creep.
creep-rupture embrittlement.
Embrittlement under creep conditions of, for example, aluminum alloys and steels that results in abnormally low rupture ductility. In aluminum alloys, iron in amounts above the solubility limit is known to cause such embrittlement; in steels, the phenomenon is related to the amount of impurities (for example. phosphorus, sulfur, copper, arsenic, antimony, and tin) present. In either case, failure occurs by intergranular cracking of the embrittled material. creep-rupture strength.
The stress that will cause fracture in a creep test at a given time in a specified constant environment. Also called stress-rupture strength. crevice corrosion.
Localized corrosion of a metal surface at, or immediately adjacent to, an area that is shielded from full exposure to the environment because of close proximity between the metal and the surface of another material. critical anodic current density.
The maximum anodic current density observed in the active region for a metal or alloy electrode that exhibits active-passive behavior in an environment. critical flaw size.
The size of a flaw (defect) in a structure that will cause failure at a particular stress level.
critical humidity.
The relative humidity above which the atmospheric corrosion rate of some metals increases sharply.
critical pitting potential (Ecp, Ep, Epp).
The lowest value of oxidizing potential at which pits nucleate and grow. It is dependent on the test method used. current.
The net transfer of electric charge per unit time. Also called electric current. See also current density. current density.
The current flowing to or from a unit area of an electrode surface, generally expressed as amps per sq ft or milliamperes per sq ft (also milliamps per sq cm, etc). current efficiency.
The ratio of the electrochemical equivalent current density for a specific reaction to the total applied current density.
- D -
deactivation.
The process of prior removal of the active corrosive constituents usually oxygen, from a corrosive liquid by controlled corrosion of expendable metal or by other chemical means, thereby making the liquid less corrosive. dealloying.
The selective corrosion of one or more components of a solid solution alloy, usually in the form of ions. Also called parting or selective leaching. See also decarburization, decobaltification, denickelification, dezincification, and graphitic corrosion. dealuminization
The selective leaching or corrosion of a specific constituent (Al, Ni, Mo, Ni) from an alloy.
decarburization.
Loss of carbon from the surface layer of a carbon-containing alloy due to reaction with one or more chemical substances in a medium that contacts the surface. See also dealloying.
decobaltification.
Corrosion in which cobalt is selectively leached from cobalt-base alloys, such as Stellite, or from cemented carbides. See also dealloying and selective leaching.
decomposition potential (or voltage).
The potential of a metal surface necessary to decompose the electrolyte of a cell or a component/substance thereof. deep groundbed.
One or more anodes installed vertically at a nominal depth of 15 m (50 ft) or more below the earth's surface in a drilled hole for the purpose of supplying cathodic protection for an underground or submerged metallic structure. See also groundbed. delta ferrite. See ferrite.
demineralization
Removal of dissolved mineral matter, generally from water.
dendrite.
A crystal that has a treelike branching pattern, being most evident in cast metals, slowly cooled through the solidification range. denickelification.
Corrosion in which nickel is selectively leached from nickel-containing alloys. Most commonly observed in copper-nickel alloys after extended service in fresh water. See also dealloying, and selective Ieaching.
density (of gases).
The mass of a unit volume of a gas at a stated temperature and pressure. density (of solids and liquids).
The mass of unit volume of a material at a specified temperature. deoxidizing.
(1) The removal of oxygen from molten metals by use of suitable deoxidixers. (2) Sometimes refers to the removal of undesirable elements other than oxygen by the introduction of elements or compounds that readily react with them. (3) In metal finishing, the removal of oxide films from metal surfaces by chemical or electrochemical reaction. depolarization.
A decrease in the polarization of an electrode; the elimination or reduction of polarization by physical or chemical means; depolarization results in increased corrosion. depolarizer.
A substance that produces depolarization.
deposit
Foreign substance which comes from the environment, adhering to a surface of a material deposit attack
Pitting corrosion resulting from deposits on a metal surface which cause concentration cells.
deposit corrosion.
Corrosion occurring under or around a discontinuous deposit on a metallic surface. Also called poultice corrosion. descaling.
Removing the thick layer of oxides formed on some metals at elevated temperatures. dezincification.
Corrosion in which zinc is selectively leached from zinc-containing alloys. Most commonly found in copper-zinc alloys containing less than 83% copper after extended service in water containing dissolved oxygen; the parting of zinc from an alloy (in some brasses, zinc is lost leaving a weak, brittle, porous, copper rich residue behind) See also dealloying and selective leaching.
dichromate treatment.
A chromate conversion coating produced on magnesium alloys in a boiling solution of sodium dichromate. dielectric shield.
In a cathodic protection system, in electrically nonconductive material, such as a coating, plastic sheet or pipe that is placed between an anode and an adjacent cathode to avoid current wastage and to improve current distribution, usually on the cathode.
differential aeration cell.
An electrolytic cell, the electromotive force of which is due to a difference in air (oxygen) concentration at one electrode as compared with that at another electrode of the same material; an oxygen concentration cell (a cell resulting from a potential difference caused by different amounts of oxygen dissolved at two locations). See also concentration cell. diffusion.
(l) Spreading of a constituent in a gas, liquid, or solid, tending to make the composition of all parts uniform. (2) The spontaneous movement of atoms or molecules to new sites within a material. diffusion coating.
Any process whereby a base metal or alloy is either (1) coated with another metal or alloy and heated to a sufficient temperature in a suitable environment or (2) exposed to a gaseous or liquid medium containing the other metal or alloy, thus causing diffusion of the coating or of the other metal or alloy into the base metal with resultant changes in the composition and properties of its surface. diffusion coefficient.
A factor of proportionality representing the amount of substance diffusing across a unit area through a unit concentration gradient in unit time. diffusion-limited current density.
The current density, often referred to as limiting current density, that corresponds to the maximum transfer rate that a particular species can sustain because of the limitation of diffusion.
dimple rupture.
A fractographic term describing ductile fracture that occurs through the formation and coalescence of microvoids along the fracture path. The fracture surface of such a ductile fracture appears dimpled when observed at high magnification and usually is most clearly resolved when viewed in a scanning electron microscope.
disbandment.
The destruction of adhesion between a coating and the surface coated. discontinuity.
Any interruption in the normal physical structure or configuration of a part, such as cracks, laps, seams, inclusions, or porosity. A discontinuity may or may not affect the usefulness of the part. dislocation.
A linear imperfection in a crystalline array of atoms. Two basic types are recognized: (1) an edge dislocation corresponds to the row of mismatched atoms along the edge formed by an extra, partial plane of atoms within the body of a crystal; (2) a screw dislocation corresponds to the axis of a spiral structure in a crystal, characterized by a distortion that joins normally parallel planes together to form a continuous helical ramp (with a pitch of one interplanar distance) winding about the dislocation. Most prevalent is the so-called mixed dislocation, which is any combination of an edge dislocation and a screw dislocation. double layer
The interface between an eletrode or a suspended particle and an electrolyte created by
charge-charge interaction (charge separation) leading to an alignment of oppositely charged ions at the surface of the electrode or particle. The simplest model is represented by a parallel plate condenser of 2 x 10-8 cm in thickness. In general the electrode will be positively charged with respect to the solution.. drainage.
Conduction of electric current from an underground metallic structure by means of a metallic conductor. Forced drainage is that applied to underground metallic structures by means of an applied electromotive force or sacrificial anode. Natural drainage is that from an underground structure to a more negative (more anodic) structure, such as the negative bus of a trolley substation. dry corrosion.
See gaseous corrosion.
drying oil.
An oil capable of conversion from a liquid to a solid by slow reaction with oxygen in the air.
ductile fracture.
Fracture characterized by tearing of metal accompanied by appreciable gross plastic deformation and expenditure of considerable energy. Contrast with brittle fracture. ductility.
The ability of a material to deform plastically without fracturing, measured by elongation or reduction of area in a tensile test, by height of cupping in an Erichsen test, or by other means.
dummy cathode.
(1) A cathode, usuully corrugated to give variable current densities, that is plated at low current densities to preferentially remove impurities from a plating solution. (2) A substitute cathode that is used during adjustment of operating conditions. dummying.
Plating with dummy cathodes. dynamic equilibrium
The condition of an electrode when the rate of anodic dissolution just balances the rate of cathodic plating.
- E -
885 °F (475 °C ) embrittlement.
Embrittlement of stainless steels upon extended exposure to temperatures between 400 and 510 °C (750 and 950 °F). This type of embrittlement is caused by fine, chromium-rich precipitates that segregate at grain boundaries; time at temperature directly influences the amount of segregation Grain-boundary segregation of the chromium rich precipitates increases strength and hardness, decreases ductility and toughness, and changes corrosion resistance. This type of embrittlement can be reversed by heating above the precipitation range. elastic deformation.
A change in dimensions directly proportional to and in phase with an increase or decrease in applied force. elasticity.
The property of a material by virtue of which deformation caused by stress disappears upon removal of the stress. A perfectly elastic body completely recovers its original shape and dimensions after release of stress. elastic limits.
The maximum stress that a material is capable of sustaining without any permanent strain (deformation) remaining upon complete release of the stress. elastomer.
A natural or synthetic polymer, which at room temperature can be stretched repeatedly to at least twice its original length, and which after removal of the tensile load will immediately and forcibly return to approximately its original length. electrical conductivity. See conductivity. electrical isolation.
The condition of being electrically separated from other metallic structures or the environment.
electrical resistivity.
The electrical resistance offered by a material to the flow of current, times the cross-sectional area of current flow and per unit length of current path; the reciprocal of the conductivity. Also called resistivity or specific resistance. electrochemical admittance.
The inverse of electrochemical impedance. electrochemical cell.
An electrochemical system consisting of an anode and a cathode in metallic contact and immersed in an electrolyte. (The anode and cathode may be different metals or dissimilar areas on the same metal surface). electrochemical corrosion.
Corrosion that is accompanied by a flow of electrons between cathodic and anodic areas on metallic surfaces.
electrochemical equivalent.
The weight of an element or group of elements oxidized or reduced at 100~ efficiency by the passage of a unit quantity of electricity. Usually expressed as grams per coulomb. electrochemical impedance.
The frequency-dependent complex-valued proportionality factor (A￡/Ai) between the applied potential or current and the response signal. This factor is the total opposition (0 or 0 - cm2) of an electrochemical system to the passage of charge. The value is related to the corrosion rate under certain circumstances. electrochemical potential.
The partial derivative of the total electrochemical free energy of a constituent with respect to the number of moles of this constituent where all factors are kept constant. It is analogous to the chemical potential of a constituent except that it includes the electric as well as chemical contributions to the free energy. The potential of an electrode in an
electrolyte relative to a reference electrode measured under open circuit conditions. electrochemical series.
Same as electromotive force series. electrode.
(1) An electronic conductor used to establish electrical contact with an electrolytic part of a circuit. (2) An electronic conductor in contact with an ionic conductor. electrode polarization.
Change of electrode potential with respect to a reference value. Often the free corrosion potential is used as the reference value. The change may be caused, for example, by the application of an external electrical current or by the addition of an oxidant or reductant. electrodeposition.
The deposition of a substance on an electrode by passing electric current through an electrolyte.
electrode potential.
The potential of an electrode in an electrolyte as measured against a reference electrode. The electrode potential does not include any resistance losses in potential in either the solution or external circuit. It represents the reversible work to move a unit charge from the electrode surface through the solution to the reference electrode. electrode reaction.
Interfacial reaction equivalent to a transfer of charge between electronic and ionic conductors. See also anodic reaction and cathodic reaction.
electrogalvanizing.
The electroplating of zinc upon iron or steels electrokinetic potentials.
This potential, sometimes called zeta potential, is a potential difference in the solution caused by residual, unbalanced charge distribution in the adjoining solution, producing a double layer. The electrokinetic potential is different from the electrode potential in that it occurs exclusively in the solution phase; that is, it represents the reversible work necessary to bring a unit charge from infinity in the solution up to the interface in question but not through the interface.
electroless plating.
A process in which metal ions in a dilute aqueous solution are plated out on a substrate by means of autocatalytic chemical reduction. electrolysis.
Production of chemical changes of the electrolyte by the passage of current through an electrochemical cell. electrolyte.
(1) A chemical substance or mixture, usually liquid, containing ions that migrate in an electric field. (2) A chemical compound or mixture of compounds which when molten or in solution will conduct an electric current. electrolytic cells.
An assembly, consisting of a vessel, electrodes, and an electrolyte, in which electrolysis can be carried out. electrolytic cleaning.
A process of removing soil, scale, or corrosion products from a metal surface by subjecting it as an electrode to an electric current in an electrolytic bath. electrolytic protections. See cathodic protection. electromotive force. Electrical potential; voltage.
electromotive force series (emf series).
A list of elements arranged according to their standard electrode potentials, with \"noble\" metals such as gold being positive and \"active\" metals such as zinc being negative. electron flow.
A movement of electrons in an external circuit connecting an anode and cathode in a corrosion cell; the current flow is arbitrarily considered to be in an opposite direction to the electron flow. electroplating.
Electrodepositing a metal or alloy in an adherent form on an object serving as a cathode. electropolishing.
A technique commonly used to prepare metallographic specimens, in which a high polish is produced by making the specimen the anode in an electrolytic cell, where preferential dissolution at high points smooths the surface. electrotinning.
Electroplating tin on an object.
embrittlement.
The severe loss of ductility or toughness or both, of a material, usually a metal or alloy. Many forms of embrittlement can lead to brittle fracture. Many forms can occur during thermal treatment or elevated temperature service (thermally induced embrittlement). Some of these forms of embrittlement, which affect steels, include blue brittleness, 885 \"F (475 \"C) embrittlement, quench-age embrittlement, sigma-phase embrittlement, strain-age embrittlement, temper embritlement, tempered martensite embrittlement, and thermal embrittlement. In addition, steels and other metals and alloys can be embrittled by environmental conditions (environmentally assisted embrittlement). The forms of environmental embrittlement include acid embrittlement, caustic embrittlement, corrosion embrittlement, creep-rupture embrittlement, hydrogen embrittlement, liquid metal embrittlement, neutron embrittlement, solder embrittlement, solid metal embrittlement, and stress-corrosion cracking.
endurance limit.
The maximum stress that a material can withstand for an infinitely large number of fatigue cycles. See also fatigue strength.
environment.
The surroundings or conditions (physical, chemical, mechanical) in which a material exists.
environmental cracking.
Brittie fracture of a normally ductile material in which the corrosive effect of the environment is a causative factor. Environmental cracking is a general term that includes corrosion fatigue, high-temperature hydrogen attack, hydrogen blistering, hydrogen
embrittlement, liquid metal embrittiement, solid metal embrittlement, stress-corrosion cracking, and sulfide stress cracking. The following terms have been used in the past in connection with environmental cracking, but are becoming obsolete: caustic embrittlement, delayed fracture, season cracking, static fatigue, stepwise cracking, sulfide corrosion cracking, and sulfide stress-corrosion cracking. See also embrittlement. environmentally assisted embrittlement. See embrittlement.
epoxy.
Resin formed by the reaction of bisphenol and epichlorohydrin. equilibrium (reversible) potential.
The potential of an electrode in an electrolytic solution when the forward rate of a given reaction is exactly equal to the reverse rate. The equilibrium potential can only be defined with respect to a specific electrochemical reaction. erosion.
Destruction of metals or other materials by the abrasive action of moving fluids, usually accelerated by the presence of solid particles or matter in suspension. When corrosion occurs simultaneously, the term erosion-corrosion is often used. erosion-corrosion.
A conjoint action involving corrosion and erosion in the presence of a moving corrosive fluid, leading to the accelerated loss of material. eutectic.
(1)An isothermal reversible reaction in which a liquid solution is converted into two or more intimately mixed solids on cooling, the number of solids formed being the same as the number of components in the system. (2) An alloy having the composition indicated by the eutectic point on an equilibrium diagram. (3) An alloy structure of intermixed solid constituents formed by a eutectic reaction. eutectoid.
(1) An isothermal reversible reaction in which a solid solution is converted into two or more intimately mixed solids on cooling, the number of solids formed being the same as the number of components in the system. (2) An alloy having the composition indicated by the eutectoid point on an equilibrium diagram. (3) An alloy structure of intermixed solid constituents formed by a eutectoid reaction.
exchange current.
When an electrode reaches dynamic equilibrium in a solution, the rate of anodic dissolution balances the rate of cathodic plating. The rate at which either positive or negative charges are entering or leaving the surface at this point is known as the exchange current.
exchange current density.
The rate of charge transfer per unit area when an electrode reaches dynamic equilibrium (at its reversible potential) in a solution; that is, the rate of anodic charge transfer (oxidation) balances the rate of cathodic charge transfer (reduction).
exfoliation.
Corrosion that proceeds laterally from the sites of initiation along planes parallel to the surface, generally at grain boundaries, forming corrosion products that force metal away
from the body of the material, giving rise to a layered appearance.
external circuit.
The wires, connectors, measuring devices, current sources, etc., that are used to bring about or measure the desired electrical conditions within the test cell. It is this portion of the cell through which electrons travel.
- F -
failure.
A general term used to imply that a part in service (1) has become completely inoperable, (2) is still operable but is incapable of satisfactorily performing its intended function, or (3) has deteriorated seriously, to the point that it has become unreliable or unsafe for continued use. Faraday's law.
(1) The amount of any substance dissolved or deposited in electrolysis is proportional to the total electric charge passed. (2) The amounts of different substances dissolved or deposited by the passage of the same electric charge are proportional to their equivalent weights. fatigue.
The phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material. Fatigue fractures are progressive and grow under the action of the fluctuating stress. fatigue crack growth rate.
The rate of crack extension caused by constant-amplitude fatigue loading, expressed in terms of crack extension per cycle of load application. fatigue life.
The number of cycles of stress that can be sustained prior to failure under a stated test condition.
fatigue limit.
The maximum stress that presumably leads to fatigue fracture in a specified number of stress cycles. If the stress is not completely reversed. the value of the mean stress. the minimum stress, or the stress ratio should also be stated. Compare with endurance limit. fatigue strength.
The maximum stress that can be sustained for a specified number of cycles without failure, the stress being completely reversed within each cycle unless otherwise staled. Ferritic
Pertaining to the body-centered cubic crystal structure (BCC) of many ferrous (iron-base) metals. ferrite.
(1) A solid solution of one or more elements in body-centered cubic iron. Unless otherwise designated (for instance, as chromium ferrite), the solute is generally assumed to be carbon. On some equilibrium diagrams, there are two ferrite regions separated by an austenite area. The lower area is alpha ferrite; the upper, delta ferrite. If there is no
designation, alpha ferrite is assumed. (2) ln the held of magnetics, substances having the general formula: MO . M2O3, the trivalent metal often being iron. filiform corrosion.
Corrosion that occurs under some coatings in the form of randomly distributed threadlike filaments. film.
A thin, not necessarily visible, layer of material.
fish eyes.
Areas on a steel fracture surface having a characteristic white crystalline appearance. flakes.
Short, discontinuous internal fissures in wrought metals attributed to stresses produced by localized transformation and decreased solubility of hydrogen during cooling after hot working. In a fracture surface. flakes appear as bright silvery areas; on an etched surface, they appear as short, discontinuous cracks. Also called shatter cracks or snow flakes. flame spraying.
Thermal spraying in which coating material is fed into an oxyfuel gas flame, where it is melted. Compressed gas may or may not be used to atomize the coating material and propel it onto the substrate. Fogged Metal
A metal whose luster has been reduced because of a surface film, usually a corrosion product layer.
foreign structure.
Any metallic structure that is not intended as part of a cathodic protection system of interest. fouling.
An accumulation of deposits. This term includes accumulation and growth of marine organisms on a submerged metal surface and also includes the accumulation of deposits (usually inorganic) on heat exchanger tubing. fouling organism.
Any aquatic organism with a sessile adult stage that attaches to and fouls underwater structures of ships. fractography.
Descriptive treatment of fracture, especially in metals, with specific reference to photographs of the fracture surface. Macrofractography involves photographs at low magnification (< 25x); microfractography, photographs at high magnification (>25x) fracture mechanics.
A quantitative analysis for evaluating structural behavior in terms of applied stress, crack length, and specimen or machine component geometry. See also linear elastic fracture mechanics. fracture toughness.
A generic term for measures of resistance to extension of a crack. The term is sometimes restricted to results of fracture mechanics tests, which are directly applicable in fracture control. However, the term commonly includes results from simple tests of notched or precracked specimens not based on fracture mechanics analysis. Results from test of the
2+
3+
latter type are often useful for fracture control, based on either service experience or empirical correlations with fracture mechanics tests. See also stress-intensity factor. free carbon.
The part of the total carbon in steel or cast iron that is present in elemental form as graphite or temper carbon. Contrast with combined carbon. free corrosion potential.
Corrosion potential in the absence of net electrical current flowing to or from the metal surface. free ferrite.
Ferrire that is formed directly from the decomposition of hypoeutectoid austenite during cooling, without the simultaneous formation of cementite. Also called proeutectoid ferrite.
free machining.
Pertains to the machining characteristics of an alloy to which one or more ingredients have been introduced to give small broken chips, lower power consumption, better surface finish, and longer tool life; among such additions are sulfur or lead to steel, lead to brass, lead and bismuth to aluminum, and sulfur or selenium to stainless steel. fretting.
A type of wear that occurs between tight-fitting surfaces subjected to cyclic relative motion of extremely small amplitude. Usually, fretting is accompanied by corrosion, especially of the very fine wear debris.
fretting corrosion.
The accelerated deterioration at the interface between contacting surfaces as the result of corrosion and slight oscillatory movement between the two surfaces; Deterioration at the interface between two contacting surfaces accelerated by relative motion between them of sufficient amplitude to produce slip. furan.
Resin formed from reactions involving furfuryl alcohol alone or in combination with other constituents.
- G -
Galvanic
Pertaining to the current resulting from the coupling of dissimilar electrodes in an electrolyte
galvanic anode.
A metal which because of its relative position in the galvanic series, provides sacrificial protection to metals that are more noble in the series, when coupled in an electrolyte. galvanic cell.
A cell in which chemical change is the source of electrical energy. It usually consists of two dissimilar conductors in contact with each other and with an electrolyte. or of two similar conductors in contact with each other and with dissimilar electrolytes. galvanic corrosion.
Accelerated corrosion of a metal because of an electrical contact with a more noble metal or nonmetallic conductor in a corrosive electrolyte. galvanic couple.
A pair of dissimilar conductors, commonly metals, in electrical contact. See also galvanic corrosion.
galvanic couple potential. See mixed potential.
galvanic current.
The electric current that flows between metals or conductive nonmetal in a galvanic couple.
galvanic series.
A list of metals and alloys arranged according to their relative corrosion potentials in a given environment. Compare with electromotive series. galvanize.
To coat a metal surface with zinc using any of various processes. galvanneal.
To produce a zinc-iron alloy coating on iron or steel by keeping the coating molten after hot dip galvanizing until the zinc alloys completely with the base metal. galvanometer.
An instrument for indicating or measuring a small electric current by means of a mechanical motion derived from electromagnetic or electrodynamic forces produced by the current. galvanostatic.
An experimental technique where by an electrode is maintained at a constant current in an electrolyte.
gaseous corrosion.
Corrosion with gas as the only corrosive agent and without any aqueous phase on the surface of the metal. Also called dry corrosion. gamma iron.
The face-centered cubic form of pure iron, stable from 910 to l400 oC (1670 to 2550 oF). general corrosion.
A form of deterioration that is distributed more or less uniformly over a surface; See uniform corrosion. Gibbs free energy.
The thermodynamic function 3G = 5H - TSS, where H is enthalpy, T is absolute temperature. and S is entropy. Also called free energy, free enthalpy, or Gibbs function. glass electrode.
A glass membrane electrode used to measure pH or hydrogen-ion activity. grain.
An individual crystal in a polycrystalline metal or alloy; it may or may not contain twinned regions and subgrains; a portion of a solid metal (usually a fraction of an inch in size), in which the atoms are arranged in an orderly pattern. grain boundary.
A narrow zone in a metal corresponding to the transition from one crystallographic
orientation to another, thus separating one grain from another; the atoms in each grain are arranged in an orderly pattern; the irregular junction of two adjacent grains is known as a grain boundary.
grain-boundary corrosion.
Same as intergranular corrosion. See also interdendritic corrosion. graphitic corrosion.
Deterioration of gray cast iron in which the metallic constituents are selectively leached or converted to corrosion products leaving the graphite intact. The term graphitization is commonly used to identify this form of corrosion, but is not recommended because of its use in metallurgy for the decomposition of carbide to graphite. See also dealloying and selective leaching. graphitization.
A metallurgical term describing the formation of graphite in iron or steel, usually from decomposition of iron carbide at elevated temperatures. Not recommended as a term to describe graphitic corrosion. green liquor.
The liquor resulting from dissolving molten melt irom the kraft recovery furnace in water. See also kraft process and smelt. Green Rot
A form of high-temperature corrosion of chromium-bearing alloys in which green chromium oxide (Cr2O3) forms, but certain other alloy constituents remain metallic; some simultaneous carburization is sometimes observed. groundbed.
A buried item, such as junk steel or graphite rods, that serves as the anode for the cathodic protection of pipelines or other buried structures. See also deep groundbed.
- H -
half cell.
An electrode immersed in a suitable electrolyte, designed for measurements of electrode potential; A pure metal in contact with a solution of known concentration of its own ion, at a specific temperature develops a potential which is characteristic and reproducible; when coupled with another half cell, an overall potential develops which is the sum of both half cells. halogen.
Any of the elements of the halogen family, consisting of fluorine, chlorine, bromine, iodine, and astatine. hard chromium.
Chromium plated for engineering rather than decorative applicactions. hardenability.
The relative ability of a ferrous alloy to form martensite when quenched from a temperature above the upper critical temperature. Hardenability is commonly measured as the distance below a quenched surfsce at which the metal exhibits a specific hardness (50 HRC, for example) or a specific percentange of martensite in the microstructure.
hardfacing.
Depositing filler metal on a surfsae by welding, spraying, or braze welding to increase resistance to abrasion, erosion, wear, galling. impact, or cavitation damage. hard water.
Water that contains certain salts, such as those of calcium or magnesium, which form insoluble deposits in boilers and form precipitates with soap. heat-affected zone.
That portion of the base metal that was not melted during brazing, cutting, or welding, but whose microstructure and mechanical properties were altered by the heat; Refers to area adjacent to a weld where the thermal cycle has coused microstructural changes which generally affect corrosion behavior. heat check.
A pattern of parallel surface cracks that are formed by alternate rapid heating and cooling of the extreme surface metal, sometimes found on forging dies and piercing punches. There may be two sets of parallel cracks one set perpendicular to the other. hematite.
(1) An iron mineral crystallizing in therhombohedral system; the most important oreof iron. (2) An iron oxide, Fe,O,, corrcsponding to an iron content of approximately 70%. high-temperature hydrogen attack.
A loss ofstrength and ductility of .steel by high-temperature reaction of absorhcd hydrogen with carbides in the steel resulting in dec arbwri:.alien and internal fissuring. holidays.
Discontinuities in ci coating (suchasporosity, cracks, gape. and similar Bawd) that allow areas of base metal to be exposed to any corrosive environment that contacts the coated surface.
hot corrosion.
An accelerated corrosion of' metal surfaces that results from the combined elTect of oxidation and reactions with sulfur compounds and other contaminunts, such us chlorides, to form a molten salt on a metal iurfuce that f1uxes, destroys, or disrupts the normal protective oxide. Seealso gaseous r erosion.
hot cracking.
Also called solidification crackinghot cracking of weldments is caused by the segregation at grain boundaries of low-melting constituents in the weld metal. This can resultin grain-boundary tearing under thermal contraction stresses. Hot cracking can be minimized bythe use of low-impurity welding materials and proper joint design. See also cold cracl ing, lamellar tearing, and stress-relief cracl ing. hot working.
Deforming metal plastically at sucha temperature and strain rate that recrystallization takes place simultaneously with the deformation, thus avoiding any strain hardening.Contrast with c old ii orking. hot dip coating.
A metallic coating obtained bydipping the base metal into a molten metal. hot shortness.
A tendency for some alloys to separate along grain boundaries when stressed ordeformed
at temperatures near the melting point.Hot shortness is caused by a low-melting constituent, often present only in minute amounts,that is segregated at grain boundaries. huey test.
Corrosion testing in a boiling solution of nitric acid. This test is mainly used to detect the susceptibilty to intergranular corrosion of stainless steel. humidity test.
A corrosion test involving exposureof specimens at controlled levels of humidity and temperature. Contrast with salt-fog test. hydrogen-assisted cracking (HAC). See hydrogenembriltlement.
hydrogen-assisted stress-corrosion cracking (HSCC). See hydrogen embrittlement.
hydrogen blistering.
The formation of blisters on or below a metal surface from excessive internal hydrogen pressure; Formation of blister-like bulges on a ductile metal surface caused by internal hydrogen pressures. Hydrogen may beformed during cleaning, plating, corrosion, and so forth.
hydrogen damage.
A general term for the emhrittlement, cracking, blistering. and hydride formation that can occur when hydrogen is present in some metals. hydrogen disintegration
Deep internal cracks caused by hydrogen. hydrogen embrittlement.
A process resulting in adecrease of the toughness or ductility of a metal due to the presence of atomic hydrogen. Hydrogen embrittlement has been recognized classically as being of two types. The first known as internal hydrogen embrittlement, occurs when the hydrogen enters molten metal which becomes supersaturated with hydrogen immediately after solidification. The second type, environmental hydrogen embrittlement, results from hydrogen being absorbed by solid metals. This can occur during elevated-temperature thermal treatments and in service during electroplating, contact with maintenance chemicals, corrosion reactions, cathodic protection, and operating in high-pressure hydrogen. In the absence of residual stress or external loading, environmental hydrogen embrittlement is manifested in various forms, such as blistering, internal cracking, hydride formation, and reduced ductility. With a tensile stress or stress-intensity factor exceeding a specific threshold, the atomic hydrogen interacts with the metal to induce subcritical crackgrowth leading to fracture. In the absence of a corrosion reaction (polarized cathodically), the usual term used is hydrogen-assisted cracking(HAC) or hydrogen stress cracking (HSC). In the prcsence of active corrosion, usually as pits or crevices (polarized anodically), the cracking is generally called stress-corrosion cracking(SCC), but should more properly be called hydrogen-assisted stress-corrosion cracking (HSCC). Thus HSC and electrochemically anodic SCC can operate separately or in combination(HSCC). In some metals, such as high-strength steels, the mechanism is believed to be all, or nearly all, HSC. The participating mechanism of HSC is not always recognized and may be evaluated under the generic heading of SCC.
hydrogen-induced cracking (HIC).
Same as hydrogen embrittlement. hydrogen overvoltage.
Overvoltage associated with the liberation of hydrogen gas. hydrogen stress cracking (HSC). See hydrogen embrittlement. hydrolysis.
(1) Decomposition or alteration of a chemical substance by water. (2) In aqueous solutions of electrolytes, the reactions of cations with water to produce a weak base or of anions to produce a weak acid.
hydrophilic.
Having an affinity for water. Contrast with hydrophobic.
hydrophobic.
Lacking an affinity for, repelling, orfailing to absorb or adsorb water. Contrast with hydrophilic. hygroscopic.
(1) Possessing a marked ability to accelerate the condensation of water vapor; applied to condensation nuclei composed of salts that yield aqueous solutions of a very low equilibrium vapor pressure compared with that of pure water at the same temperature. (2) Pertaining to a substance whose physical characteristics are appreciably altered by effects of water vapor. (3) Pertaining to water absorbed by dry soil minerals from the atmosphere; the amounts depend on the physicochemical character of the surfaces, and increase with rising relative humidity.
- I -
immersion plating.
Depositing a metallic coating on a metal immersed in a liquid solution, without the aid of an external electric current. Also called dip plating. immunity.
A state of resistance to corrosion or anodic dissolution of a metal caused by thermodynamic stability of the metal. impingement corrosion.
A form of erosion-corrosion generally associated with the local impingement of a high-velocity. Flowing fluid against a solid surface. impressed current.
Direct current supplied by a device employing a power source external to the electrode system of a cathodic protection installation. inclusions.
Particles of foreign material in a metallic matrix. The particles are usually compounds (such as oxides, sulfides, or silicates), but may be of any substance that is foreign to (and essentially insoluble in) the matrix. incubation period.
A period prior to the detection of corrosion while the metal is in contact with a
corrodent.
industrial atmosphere.
An atmosphere in an area of heavy industry with soot, fly ash, and sulfur compounds as the principal constituents. inert anode.
An anode that is insoluble in the electrolyte under the conditions prevailing in the electrolysis. inhibitor.
A chemical substance or combination of substances that, when present in the environment, prevents or reduces corrosion without significant reaction with the components of the environment. inorganic.
Being or composed of matter other than hydrocarbons and their derivatives, or matter that is not of plant or animal origin. Contrast with organic. inorganic zinc-rich paint.
Coating containing a zinc powder pigment in an inorganic vehicle. intensiostatic. See galvanostatic.
intercrystalline corrosion. See intergranular corrosion. intercrystalline cracking. See intergranular cracking. interdendritic corrosion.
Corrosive attack that progresses preferentially along interdendritic paths. This type of attack results from local differences in composition, such as coring commonly encountered in alloy castings. intergranular.
Between crystals or grains. Also called intercrystalline. Contrast with transgranular. intergranular corrosion.
Corrosion occurring preferentially at grain boundaries, usually with slight or negligible attack on the adjacent grains. Also called intercrystalline corrosion. intergranular cracking.
Cracking or fracturing that occurs between the grains or crystals in a polycrystalline aggregate. Also called intercrystalline cracking. Contrast with transgranular cracking. intergranular fracture.
Brittle fracture of a metal in which the fracture is between the grains, or crystals, that form the metal. Also called intercrystalline fracture. Contrast with transgranular fracture.
intergranular stress-corrosion cracking (IGSCC).
Stress-corrosion cracking in which the cracking occurs along grain boundaries. intermediate electrode. Same as bipolar electrode. internal oxidation.
The formation of isolated particles of corrosion products beneath the metal surface.
This occurs as the result of preferential oxidation of certain alloy constituents by inward diffusion of oxygen, nitrogen, sulfur, and so forth. intumescence.
The swelling or bubbling of a coating usually because of heating (term currently used in space and fire protection applications). ion.
An atom, or group of atoms, that has gained or lost one or more outer electrons and thus carries an electric charge. Positive ions, or cations, are deficient in outer electrons. Negative ions, or anions, have an excess of outer electrons. Ion Erosion
Deterioration of material caused by ion impact. ion exchange.
The reversible interchange of ions between a liquid and solid, with no substantial structural changes in the solid. iron rot.
Deterioration of wood in contact with iron-based alloys. isocorrosion diagram.
A graph or chart that shows constant corrosion behavior with changing solution (environment) composition and temperature.
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KISCC.
Abbreviation for the critical value of the plane strain stress-intensity factor that will produce crack propagation by stress-corrosion cracking of a given material in a given environment. knife-line attack.
Intergranular corrosion of an alloy, usually stabilized stainless steel, along a line adjoining or in contact with a weld after heating into the sensitization temperature range. kraft process.
A wood-pulping process in which sodium sulfate is used in the caustic soda pulp-digestion liquor. Also called kraft pulping or sulfate pulping.
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lamellar corrosion. See exfoliation corrosion. lamellar tearing.
Occurs in the base metal adjacent to weldments due to high through-thickness strains introduced by weld metal shrinkage in highly restrained joints. Tearing occurs by decohesion and linking along the working direction of the base metal; cracks usually run roughly parallel to the fusion line and are steplike in appearance. Lamellar tearing
can be minimized by designing joints to minimize weld shrinkage stresses and joint restraint. See also cold cracking, hot cracking, and stress-relief cracking. Langelier saturation index.
An index calculated from total dissolved solids, calcium concentration, total alkalinity, pH and solution temperature that shows the tendency of a water solution to precipitate or dissolve calcium carbonate. ledeburite.
The eutectic of the iron-carbon system, the constituents of which are austenite and cementite. The austenite decomposes into ferrite and cementite on cooling below the temperature at which transformation of austenite to ferrite or ferrite plus cementite is completed. ligand.
The molecule, ion, or group bound to the central atom in a chelate or a coordination compound.
limiting current density.
The maximum current density that can be used to obtain a desired electrode reaction without undue interference such as from polarization. linear elastic fracture mechanics.
A method of fracture analysis that can determine the stress (or load) required to induce fracture instability in a structure containing a cracklike flaw of known size and shape. See also fracture mechanics and stress-intensity factor. lipophilic.
Having an amenity for oil. See also hydrophilic and hydrophobic. liquid metal embrittlement.
Catastrophic brittle failure of a normally ductile metal when in contact with a liquid metal and subsequently stressed in tension. local action.
Corrosion due to the action of \"local cells,\" that is, galvanic cells resulting from inhomogeneities between adjacent areas on a metal surface exposed to an electrolyte. local cell.
A galvanic cell resulting from inhomogeneities between areas on a metal surface in an electrolyte. The inhomogeneities may be of physical or chemical nature in either the metal or its environment. localized corrosion.
Corrosion at discrete sites, stress-corrosion cracking. long-line current.
Current that flows through the earth from an anodic to a cathodic area of a continuous metallic structure. Usually used only where the areas are separated by considerable distance and where the current results from concentration-cell action. luggin probe (Luggin Haber capillary).
A small tube or capillary filled with electrolyte, terminating close to the metal surface under study, and used to provide an ionically conducting path without diffusion between an electrode under study and a reference electrode.
- M -
macroscopic.
Visible at magnifications to 25x. macrostructure.
The structure of metals as revealed by macroscopic examination of the etched surface of a polished specimen. magnetite.
Naturally occurring magnetic oxide of iron (Fe3O4). martensite.
A generic term for microstructures formed by diffusionless phase transformation in which the parent and product phases have a specific crystallographic relationship. Martensite is characterized by an acicular pattern in the microstructure in both ferrous and nonferrous alloys. In alloys where the solute atoms occupy interstitial positions in the martensitic lattice (such as carbon in iron), the structure is hard and highly strained; but where the solute atoms occupy substitutional positions (such as nickel in iron), the martensite is soft and ductile. The amount of high-temperature phase that transforms to martensite on cooling depends to a large extent on the lowest temperature attained, there being a rather distinct beginning temperature (Ms) and a temperature at which the transformation is essentially complete (Mf). mechanical plating.
Plating wherein fine metal powders are peened onto the work by tumbling or other means. metal dusting.
Accelerated deterioration of metals in carbonaceous gases at elevated temperatures to form a dustlike corrosion product; a unique form of high temperature corrosion which forms a dust-like corrosion product and sometimes develops hemispherical pits on a susceptible metal surface; simultaneous carburization is generally observed. metal ion concentration cell
A galvanic cell caused by a difference in metal ion concentration at two locations on the same metal surface. metallic glass.
An alloy having an amorphous or glassy structure. See also amorphous solid. metallizing.
(1) The application of an electrically conductive metallic layer to the surface of nonconductors. (2) The application of metallic coatings by nonelectrolytic procedures such us spraying of molten metal and deposition from the vapor phase. meteor perforation
Perforation of material in outer space resulting from meteor strikes. microbial corrosion. See biological corrosion. microscopic.
Visible at magnifications above 25x.
microstructure.
The structure of a prepared surface of a metal as revealed by a microscope at a magnification exceeding 25x. mill scale.
The heavy oxide layer formed during hot fabrication or heat treatment of metals. mixed potential.
The potential of a specimen (or specimens in a galvanic couple) when two or more electrochemical reactions are occurring. Also called galvanic couple potential. molal solution.
Concentration of a solution expressed in moles of solute divided by 1000 g of solvent. molar solution.
Aqueous solution that contains 1 mole (gram-molecular weight) of solute in 1 L of the solution. mole.
One mole is the mass numerically equal (in grams) to the relative molecular mass of a substance. It is the amount of substance of a system that contains as many elementary units (6.023 exp23) as there are atoms of carbon in 0.012 kg of the pure nuclide C12; the elemenary unit must be specified and may be an atom, molecule, ion, electron, photon, or even a specified group of such units. moneypenny-strauss test.
Corrosion testing in a copper-sulfate solution containing sulfuric acid. Used to detect the susceptibility of stainless steel to intergranular corrosion. monomer.
A molecule usually an organic compound, having the ability to join with a number of identical molecules to form a polymer.
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natural aging.
Spontaneous aging of a supersaturated solid solution at room temperature. See also aging. Compare with artificial aging. Nernst equation.
An equation that expresses the exact electromotive force of a cell in terms of the activities of products and reactants of the cell. Nernst layer, Nernst thickness.
The diffusion layer or the hypothetical thickness of this layer as given by the theory of Nernst, is defined by:
id = n F D (C - C)/
where, id = the diffusion limited current density, D = the diffusion coefficient, C = the concentration at the electrode surface, and = the Nernst thickness. It is a
hypothetical thickness which has been found to be 0.05 cm in many cases of unstirred aqueous electrolytes. neutron embrittlement.
Embrittlement resulting from bombardment with neutrons, usually encountered in
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metals that have been exposed to a neutron flux in the core of a reactor. In steels, neutron embrittlement is evidenced by a rise in the ductile-to-brittle transition temperature. nitriding.
Introducing nitrogen into the surface layer of a solid ferrous alloy by holding at a suitable temperature (below Ac1 for ferritic steels) in contact with a nitrogenous material, usually ammonia or molten cyanide of appropriate composition. Quenching is not required to produce a hard case. nitrocarburizing.
Any of several processes in which both nitrogen and carbon are absorbed into the surface layers of a ferrous material at temperatures below the lower critical temperature and, by diffusion, create a concenteration gradient. Nitrocarburizing is performed primarily to provide an antiscuffling surface layer and to improve fatigue resistance. Comparc with carbonitriding. noble.
The positive direction of electrode potential, thus resembling noble metals such as gold and platinum. noble metal.
(1) A metal whose potential is highly positive relative to the hydrogen electrode. (2) A metal with marked resistance to chemical reaction, particularly to oxidation and to evolution by inorganic acids. The term as often used is synonymous with precious metal.
noble potential.
A potential more cathodic (positive) than the standard hydrogen potential. normalizing.
Heating a ferrous alloy to a suitable temperature above the transformation range and then cooling in air to a temperature substantially below the transformation range. normal solution.
An aqueous solution containing one gram equivalent of the active reagent in 1L of the solution. normal stress.
The stress component perpendicular to a plane on which forces act. Normal stress may be either tensile or compresssive.
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open-circuit potential.
The potential of an electrode measured with respect to a reference electrode or another electrode when no current flows to or from it. organic.
Being or composed of hydrocarbons or their derivatives, or matter of plant or animal origin. Contrast with inorganic. organic acid.
A chemical compound with one or more carboxyl radicals (COOH) in its structure;
examples are butyric acid, CH3(CH2)2COOH; maleic acid, HOOCCH-CHCOOH; and benzoic acid, C6H5COOH. organic zinc-rich paint.
Coating containing zinc powder pigment andan organic resin. overaging.
Aging under conditions of time and temperature greater than those required to obtain maximum change in a certain property, so that the property is altered in the direction of the initial value.,/dd> oveheating.
Heating a metal or alloy to such a high temperature that its properties are impaired. When the original properties cannot be restored by further heat treating, by mechanical working, or by a combination of working and heat treating, the overheating is known as burning. overvoltage.
The difference between the actual electrode potential when appreciable electrolysis begins and the reversible electrode potential. oxidation.
(1) A reaction in which there is an increase in valence resulting from a loss of electrons. Contrast with reduction. (2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air. oxidized surface (on steel).
Surface having a thin, tightly adhering, oxidized skin (from straw to blue in color), extending in from the edge of a coil or sheet. oxidizing agent.
A compound that causes oxidation, thereby itself being reduced. oxygen concentration cell.
A galvanic cell resulting from difference in oxygen concentration between two locations; See differential aeration cell. ozone.
A powerfully oxidizing allotropic form of the element oxygen. The ozone molecule contains three atoms (O3). Ozone gas is decidedly blue, and both liquid and solid ozone are an opaque blue-black color, similar to that of ink.
- P -
partial annealing.
An imprecise term used to denote a treatment given cold-worked material to reduce its strength to a controlled level or to effect stress relief. To be meaningful, the type of material, the degree of cold work, and the time-temperature schedule must be stated. parting.
The selective attack of one or more components of a solid solution alloy; eg. dezincification, dealumination etc. See dealloying. parts per billion.
A measure of proportion by weight, equivalent to one unit weight of a material per
billion (10) unit weights of compound. One part per billion is equivalent to 1 mg/kg. parts per million.
A measure of proportion by weight, equivalent to one unit weight of a material per million (10) unit weights of compound. One part per million is equivalent to l mg/g passivation.
(1) A reduction of the anodic reaction rate of an electrode involved in corrosion. (2) The process in metal corrosion by which metals become passive. (3) The changing of a chemically active surface of' a metal to a much less reactive state. Contrast with activation. passivator.
A type of inhibitor that appreciably changes the potential of u metal to a more noble (positive) value. passive.
(1) A metal corroding under the control of a surface reaction product. (2) The state of the metal surface characterized by low corrosion rates in a potential region that is strongly oxidizing for the metal. (3) The state of a metal when its behavior is much more noble than its position in the EMF series would predict. This is a surface phenomena. passive-active cell.
(1) A cell, the emf of which is due to the potential difference between a metal in an active state and the same metal in a passive state. (2) A corrosion cell in which the anode is a metal in the active state and the cathode is the same metal in the passive state. passivity.
A condition in which a piece of metal, because of an impervious covering of oxide or other compound, has a potential much more positive than that at the metal in the active state. patina.
The coating, usually green, that forms on the surface of metals such as copper and copper alloys exposed to the atmosphere. Also used to describe the appearance of a weathered surface of any metal. pearlite.
A metastable lamellar aggregate of ferrite and cementite resulting from the transformation of austenite at temperatures above the bainite range. phosphating.
Forming an adherent phosphate coating on a metal by immersion in a suitable aqueous phosphate solution. Also called phosphatizing. See also conversion coating. pH.
A measure of the acidity or alkalinity of a solution; The negative logarithm of the hydrogen-ion activity; it denotes the degree of acidity or basicity of a solution. At 25 oC (77 oF), 7.0 is the neutral value. Decreasing values below 7.0 indicate increasing acidity; increasing values above 7.0, increasing basicity. physical vapor deposition.
A coating process whereby the cleaned and masked component to be coated is
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heated and rotated on a spindle above the streaming vapor generated by melting and evaporating a coating material source bar with a focused electron beam in an evacuated chamber. physisorption.
The binding of an adsorbate to the surface of a solid by forces whose energy levels approximate those of condensation. Contrast with chemisorption. pickle.
A solution or process used to loosen or remove corrosion products such as scale or tarnish. pickling.
Removing surface oxides from metals by chemical or electrochemical reaction. pitting.
Localized corrosion of a metal surface, confined to a point or small area, that takes the form of cavities or pits. pitting factor.
Ratio of the depth of the deepest pit resulting from corrosion divided by the average penetration as calculated from weight loss. plane strain.
The stress condition in linear elastic fracture mechanics in which there is zero strain in a direction normal to both the axis of applied tensile stress and the direction of crack growth (that is, parallel to the crack front); most nearly achieved in loading thick plates along a direction parallel to the plate surface. Under plane-strain conditions, the plane of fracture instability is normal to the axis of the principal tensile stress. plane stress.
The stress condition in linear elastic fracture mechanics in which the stress in the thickness direction is zero; most nearly achieved in loading very thin sheet along a direction parallel to the surface of the sheet. Under plane-stress conditions, the plane of fracture instability is inclined 45o to the axis of the principal tensile stress. plasma spraying.
A thermal spraying process in which the coating material is melted with heat from a plasma torch that generates a nontransferred arc: molten coating material is propelled against the base metal by the hot, ionized gas issuing from the torch. plastic deformation.
The permanent (inelastic) distortion of metals under applied stresses that strain the material beyond its elastic limit. plasticity.
The property that enables a material to undergo permanent deformation without rupture. polarization.
(1) The change from the open-circuit electrode potential as the result of the passage of current. (2) A change in the potential of an electrode during electrolysis, such that the potential of an anode becomes more noble, and that of a cathode more active, than their respective reversible potentials. Often accomplished by formation of a film on the electrode surface.
polarization admittance.
The reciprocal of polarization resistance (di/dE). polarization curve.
A plot of r urrent density versus electrode potential for a specific electrode-electrolyte combination.
polarization resistance.
The slope (dE/di) at the corrosion potential of a potential (E)/current density (i) curve. Also used to describe the method of measuring corrosion rates using this slope. polyester.
Resin formed by condensation of polybasic and monobasic acids with polyhydric alcohols. polymer.
A chain of organic molecules produced by the joining of primary units called monomers. potential.
Any of various functions from which intensity or velocity at any point in a field may be calculated. The driving influence of an electrochemical reaction. See also active potential, chemical potential, corrosion potential, critical pitting potential, decomposition potential, electrochemical potential, electrode potential, electrokinetic potential, equilibrium (reversible) potential, free corrosion potential, noble potential, open-circuit potential, protective potential, redox potential, and standard electrode potential.
potential-pH diagram.
See Pourbaix (potential-pH) diagram. potentiodynamic (potentiokinetic).
The technique for varying the potential of an electrode in a continuous manner at a preset rate. potentiostat.
An instrument for automatically maintaining an electrode in an electrolyte at a constant potential or controlled potentials with respect to a suitable reference electrode. potentiostatic.
The technique for maintaining a constant electrode potential. poultice corrosion.
A term used in the automotive industry to describe the corrosion of vehicle body parts due to the collection of road salts and debris on ledges and in pockets that are kept moist by weather and washing. Also called deposit corrosion or attack. Pourbaix (potential-pH) diagram.
A plot of the redox potential of a corroding system versus the pH of the system, compiled using thermodynamic data and the Nernst equation. The diagram shows regions within which the metal itself or some of its compounds are stable. powder metallurgy.
The art of producing metal powders and utilizing metal powders for production of' massive materials and shaped objects. precious metal.
One of the relatively scarce and valuable metals: gold, silver, and the platinum-group metals. Also called noble metal(s). precipitation hardening.
Hardening caused by the precipitation of a constituent from a supersaturated solid solution. See also age hardening and aging. precipitation heat treatment.
Artificial aging in which a constituent precipitated from a supersaturated solid solution. precracked specimen.
A specimen that is notched and subjected to alternating stresses until a crack has developed at the root of the notch. primary current distribution.
The current distribution in an electrolytic cell that is free of polarization. primary passive potential (passivation potential).
The potential corresponding to the maximum active current density (critical anodic current density) of an electrode that exhibits active-passive corrosion behavior. primer (prime coat).
The first coat of paint applied to a surface. Formulated to have good bonding and wetting characteristics; may or may not contain inhibiting pigments. principal stress (normal).
The maximum or minimum value at the normal stress at a point in a plane considered with respect to all possible orientations of the considered plane. On such principal planes the shear stress is zero. There are three principal stresses on three mutually perpendicular planes. The state of stress at a point may be (1) uniaxial, a state of stress in which two of the three principal stresses are zero, (2) biaxial, a state of stress in which only one of the three principal stresses is zero, and (3) triaxial, a state of stress in which none of the principal stresses is zero. Multiaxial stress refers to either biaxial or triaxial stress. profile.
Anchor pattern on a surface produced by abrasive blasting or acid treatment. protective potential.
The threshold value of the corrosion potential that has to be reached to enter a protective potential range. The term used in cathodic protection to refer to the minimum potential required to supress corrosion. protective potential range.
A range of corrosion potential values in which unacceptable corrosion resistance is achieved for a particular purpose.
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quench-age embrittlement.
Embrittlement of low-carbon steels resulting from precipitation of solute carbon at existing dislocations and from precipitation hardening of the steel caused by differences in the solid solubility of carbon in ferrite at different temperatures. Quench-age embrittlement usually is caused by rapid cooling of the steel from
temperatures slightly below Ac, (the temperature at which austenite begins to form), and can be minimized by quenching from lower temperatures. quench aging.
Aging induced by rapid cooling after solution heat treatment. quench cracking.
Fracture of a metal during quenching from elevated temperature. Most frequently observed in hardened carbon steel, alloy steel, or tool steel parts of high hardness and low toughness. Cracks often emanate from fillets, holes, corners, or other stress raisers and result from high stresses due to the volume changes accompanying transformation to martensite. quench hardening.
(1) Hardening suitable = alloys (most often certain copper or titanium alloys) by solution treating and quenching to develop a martensite-like structure. (2) In ferrous alloys, hardening by austenitizing and then cooling at a rate such that a substantial amount of austenite transforms to martensite. quenching.
Rapid cooling of metals (often steels) from a suitable elevated temperature. This generally is accomplished by immersion in water, oil, polymer solution, or salt, although forced air is sometimes used.
- R -
radiation damage.
A general term for the alteration of properties of a material arising from exposure to ionizing radiation (penetrating radiation), such as x-rays, gamma rays. neutrons, heavy-particle radiation, or fission fragments in nuclear fuel material. rare earth metal.
One of the group of l5 chemically similar metals with atomic numbers 57 through 7l, commonly referred to as the lanthanides.
reactive metal.
A metal that readily combines with oxygen at elevated temperatures to form very stable oxides, for example, titanium, zirconium, and beryllium. Reactive metals may also become embrittled by the interstitial absorption of oxygen, hydrogen, and nitrogen. recrystallization.
(1) Formation of a new, strain free grain structure from that existing in cold worked metal, usually accomplished by heating. (2) The change from one crystal structure to another, as occurs on heating or cooling through a critical temperature. redox potential.
The potential of a reversible oxidation-reduction electrode measured with respect to a reference electrode, corrected to the hydrogen electrode, in a given electrolyte. reducing agent.
A compound that causes reduction, thereby itself becoming oxidized.
reduction.
A reaction in which there is a decrease in valence resulting from a gain in electrons.
Contrast with oxidation.
reference electrode.
A nonpolarizable electrode with a known and highly reproducible potential used for potentiometric and voltammetric analyses. See also calomel electrode. refractory metal.
A metal having an extremely high melting point, for example, tungsten, molybdenum, tantalum, niobium, chromium, vanadium, and rhenium. In the broad sense, this term refers to metals having melting points above the range for iron, cobalt, and nickel. relative humidity.
The ratio, expressed as a percentage, of the amount of water vapor present in a given volume of air at a given temperature to the amount required to saturate the air at that temperature.
residual stress.
Stresses that remain within a body as a result of plastic deformation.
resistance.
The opposition that a device or material offers to the flow of direct current, equal to the voltage drop across the element divided by the current through the element. Also called electrical resistance. resistivity.
See electrical resistivity.
rest potential. See corrosion potential and open-circuit potential.
ringworm corrosion
Localized corrosion frequently observed in oilwell tubing in which a circumfrential attack is observed near a region of metal \"upset\". riser.
(1) That section of pipeline extending from the ocean floor up the platform. Also, the vertical tube in a steam generator convection bank that circulates water and steam upward. (2) A reservoir of molten metal connected to a casting to provide additional metal to the casting, required as the result of shrinkage before and during solidification. rust.
A visible corrosion product consisting of hydrated oxides of iron. Applied only to ferrous alloys. See also white rust.
- S -
sacrificial protection.
Reduction of corrosion of a metal in an electrolyte by galvanically coupling it to a more anodic metal; a form of cathodic protection. salt fog test.
An accelerated corrosion test in which specimens are exposed to a fine mist of a solution usually containing sodium chloride, but sometimes modified with other chemicals.
salt spray test. See salt fog test.
saturated calomel electrode.
A reference electrode composed of mercury, mercurous chloride (calomel), and a saturated aqueous chloride solution. scaling.
(1) The formation at high temperatures of thick corrosion product layers on a metal surface. (2) The deposition of water-insoluble constituents on a metal surface. season cracking.
An obsolete historical term usually applied to stress-corrosion crackling of brass. selective leaching.
Corrosion in which one element is preferentially removed from an alloy, leaving a residue (often porous) of the elements that are more resistant to the particular environment. Also called dealloying or parting. See also decarburization, decobbaltification, denickelification, dezincification, and graphitic corrosion. sensitizing heat treatment.
A heat treatment, whether accidental, intentional, or incidental (as during welding), that causes precipitation of constituents at grain boundaries, often causing the alloy to become susceptible to intergranular corrosion or intergranular stress-corrosion cracking. See also sensitization. sensitization.
In austenitic stainless steels the precipitation of chromium carbides, usually at grain boundaries, on exposure to temperatures of about 550 to 850 oC (about 1000 to 1550 oF), leaving the grain boundaries depleted of chromium and therefore susceptible to preferential attack by a corroding (oxidizing) medium. shear.
That type of force that causes or tends to cause two contiguous parts of the same body to slide relative to each other in a direction parallel to their plane of contact. shear strength.
The stress required to produce fracture in the plane of cross section, the conditions of loading being such that the directions of force and of resistance are parallel and opposite although their paths are offset a specified minimum amount. The maximum load divided by the original cross-sectional area of a section separated by shear. sigma phase.
A hard, brittle, nonmagnetic intermediate phase with a tetragonal crystal structure, containing 30 atoms per unit cell, space group P42mnm, occurring in many binary and ternary alloys of the transition elements. The composition of this phase in the various systems is not the same and the phase usually exhibits a wide range in homogeneity. Alloying with a third transition element usually enlarges the field of homogeneity and extends it deep into the ternary section. sigma-phase embrittlement.
Embrittlement of iron-chromium alloys (most notably austenitic stainless steels) caused by precipitation at grain boundaries of the hard, brittle intermetallic sigma phase during long periods of exposure to temperatures between approximately 560
and 980 oC ( 1050 and 1800 oF). Sigma-phase embrittlement results in severe loss in toughness and ductility, and can make the embrittled material susceptible to intergranular corrosion. See also sensitization. slip.
Plastic deformation by the irreversible shear displacement (translation) of one part of a crystal relative to another in a definite crystallographic direction and usually on a specific crystallographic plane. Sometimes called glide. slow strain rate technique.
An experimental technique for evaluating susceptibility to stress-corrosion cracking. It involves pulling the specimen to failure in uniaxial tension at a controlled slow strain rate while the specimen is in the test environment and examining the specimen for evidence of stress-corrosion cracking. slushing compound.
An obsolete term describing oil or grease coatings used to provide temporary protection against atmospheric corrosion. smelt.
Molten slag; in the pulp and paper industry, the cooking chemicals tapped from the recovery boiler as molten material and dissolved in the smelt tank as green liquor. S-N diagram.
A plot showing the relationship of stress, S, and the number of cycles, N, before fracture in fatigue testing. soft water.
Water that is free of magnesium or calcium salts. solder embrittlement.
Reduction in mechanical properties of a metal as a result of local penetration of solder along grain boundaries. solid-metal embrittlement.
The occurrence of embrittlement in a material below the melting point of the embrittling species. See also liquid-metal embrittlement. solid solution.
A single, solid, homogeneous crystalline phase containing two or more chemical species. solute.
The component of either a liquid or solid solution that is present to a lesser or minor extent: the component that is dissolved in thesolution. solution.
In chemistry,a homogeneous dispersion of two or more kinds of molecular or ionic species. Solution may be composed of any combination of liquids, solids, or gases, but they always consist of a single phase. solution heat treatment.
Heating an alloy to a suitable temperature, holding at that temperature long enough to cause one or more constituents to enter into solid solution, and then cooling rapidly enough to hold these constituents in solution. solution potential.
Electrode potential where half-cell reaction involves only the metal electrode and its ion. solvent.
The component of either a liquid or solid solution that is present to a greater or major extent; the component that dissolves the solute. sour gas.
A gaseous environment containing hydrogen sulfide and carbon dioxide in hydrocarbon reservoirs. Prolonged exposure to sour gas can lead to hydrogen damage, sulfide-stress cracking, and/or stress-corrosion cracking in ferrous alloys. sour water.
Waste waters containing fetid materials, usually sulfur compounds. Space Outgassing.
Release of contained gas in the vaccum of outer space. eg. rapid destructive expansion of plastics and similar materials. Space Pitting.
Pitting resulting from ablation, outgassing or meteor contact. spalling.
The spontaneous chipping, fragmentation, or separation of a surtace or surface coating. spheroidite.
An aggregate of iron or alloy carbides of essentially spherical shape dispersed throughout a matrix of ferrite. sputtering.
A coating process whereby thermally emitted electrons collide with inert gas atoms, which accelerate toward and impact a negatively charged electrode that is a target of the coating material. The impacting ions dislodge atoms of the target material, which are in turn projected to and deposited on the substrate to form the coating. stabilizing treatment.
(1) Before finishing to final dimensions, repeatedly heating a ferrous or nonferrous part to or slightly above its normal operating, temperature and then cooling to room temperature to ensure dimensional stability in service. (2) Transforming retained austenite in quenched hardenable steels, usually by cold treatment. (3) Heating a solution-treated stabilized grade of austenitic stainless steel to 870 to 900 oC (1600 to 1650 oF) to precipitate all carbon, as TiC, NbC, or TaC so that sensitization is avoided on subsequent exposure to elevated temperature. standard electrode potential.
The reversible potential for an electrode process when all products and reactions are at unit activity on a scale in which the potential for the standard hydrogen half-cell is zero. strain.
The unit of change in the size or shape of a body due to force. Also known as nominal strain.
strain-age embrittlement.
A loss in ductility accompanied by an increase in hardness and strength that occurs
when low-carbon steel (especially rimmed or capped steel) is aged following plastic deformation. The degree of embrittlement is a function of aging time and temperature, occurring in a matter of minutes at about 200 oC (400 oF), but requiring a few hours to a year at room temperature. strain aging.
Aging induced by cold working. strain hardening.
An increase in hardness and strength caused by plastic deformation at temperatures below the recrystallization range. strain rate.
The time rate of straining for the usual tensile test. Strain as measured directly on the specimen gage length is used for determining strain rate. Because strain is dimensionless, the units of strain rate are reciprocal time. stray current.
Current flowing through paths other than the intended circuit. stray-current corrosion.
Corrosion resulting from direct current flow through paths other than the intended circuit. For example, by an extraneous current in the earth. stress.
The intensity of the internally distributed forces or components of forces that resist a change in the volume or shape of a material that is or has been subjected to external forces. Stress is expressed in force per unit area and is calculated on the basis of the original dimensions of the cross section of the specimen. Stress can be either direct (tension or compression) or shear. See also residual stress. stress concentration factor (Kt).
A multiplying factor for applied stress that allows for the presence of a structural discontinuity such as a notch or hole; Kt equals the ratio of the greatest stress in the region of the discontinuity to the nominal stress for the entire section. Also called theoretical stress concentration factor. stress-corrosion cracking (SCC).
A cracking process that requires the simultaneous action of a corrodent and sustained tensile stress. This excludes corrosion-reduced sections that fail by fast fracture. It also excludes intercrystalline or transcrystalline corrosion, which can disintegrate an alloy without applied or residual stress. Stress-corrosion cracking may occur in combination with hydrogen embrittlement. stress-intensity factor.
A scaling factor, usually denoted by the symbol K, used in linear-elastic fracture mechanics to describe the intensification of applied stress at the tip of a crack of known size and shape. At the onset of rapid crack propagation in any structure containing, a crack, the factor is called the critical stress-intensity factor, or the fracture toughness. Various subscripts are used to denote different loading conditions or fracture toughnesses:
KcPlane-stress fracture toughness. The value of stress intensity at which crack propagation becomes rapid in sections thinner than those in which plane-strain
conditions prevail.
KIStress-intensity factor for a loading condition that displaced the crack faces in a direction normal to the crack plane (also known as the opening mode of deformation). KIc. Plane-strain fracture toughness. The minimum value of Kc for any given material and condition, which is attained when rapid crack propagation in the opening mode is governed by plane-strain conditions.
KIdDynamic fracture toughness. The fracture toughness determined under dynamic loading conditions; it is used as an approximation of KIc for very tough materials. KISCC. Threshold stress-intensity factor for stress-corrosion cracking. The critical plane-strain stress intensity at the onset of stress-corrosion cracking under specified conditions.
KQ. Provisional value for plane-strain fracture toughness.
Kth. Threshold stress intensity for stress-corrosion cracking. The critical stress intensity at the onset of stress-corrosion cracking under specified conditions.
K. The range of the stress-intensity factor during a fatigue cycle.
stress-intensity factor range, K..
In fatigue, the variation in the stress-intensity factor in cycle, that is, Kmax-Kmin. stress raisers.
Changes in contour or discontinuities in structure that cause local increases in stress. stress ratio, A or R.
The algebraic ratio of two specified stress values in a stress cycle. Two commonly used stress ratios are: (1) the ratio of the alternating stress amplitude to the mean stress. A = Sa/Sm and (2) the ratio of the minimum stress to the maximum stress. R =Smin/Smax.
stress-relief cracking.
Also called postweld heat treatment cracking, stress-relief cracking occurs when susceptible alloys are suhjected to thermal stress relief after welding to reduce residual stresses and improve toughness. Stress-relief cracking occurs only in metals that can precipitation-harden during such elevated-temperature exposure; it usually occurs at stress raisers, is intergranular in nature, and is generally observed in the coarse-grained region of the weld heat-affectted zone. See also cold cracking, hot cracking, and lamellar tearing. stress relieving.
Heat treatment carried out in steel to reduce internal stresses. striation.
A fatigue fracture feature, often observed in electron micrographs, that indicates the position of the crack front after each succeeding cycle of stress. The distance between striations indicates the advance of the crack front across that crystal during one stress cycle, and a line normal to the striation indicates the direction of local crack propagation. See also beach marks. subsurface corrosion.
Formation of isolated particles of corrosion products beneath a metal surface. This results from the prcferential reactions of certain alloy constituents to inward diffusion of oxygen, nitrogen, or sulfur.
sulfidation.
The reaction of a metal or alloy with a sulfur-containing species to produce a sulfur compound that forms on or beneath the surface on the metal or alloy. sulfide stress cracking.
Brittle failure by cracking under the combined action of tensile stress and corrosion in the presence of water and hydrogen sulfide. See also environmental cracking. surfactant.
A surface-active agent; usually an organic compound whose moleculei contain a hydrophilic group at one end and a lipophilic group at the other.
- T -
Tafel Line, Tafel Slope, Tafel Diagram.
An electrode when polarized frequently yields a current potential relationship over a region which can be approximated by:
h= ±B log (i/io)
where h = change in open circuit potential, i = the current density, B and io = constants. B is known as the Tafel Slope.
If this behavior is observed a plot of the semilogarithmic components is known as the Tafel line and the diagram is called the Tafel diagram.
tarnish.
Surface discoloration of a metal caused by formation of a thin film of corrosion product.
temper.
(1) In heat treatment, to reheat hardened steel or hardened cast iron to some temperature below the eutectoid temperature for the purpose of decreasing hardness and increasing toughness. The process is also sometimes applied to normalized steel. (2) In tool steels, temper is sometimes inadvisably used to denote carbon content. (3) In nonferrous alloys and in some ferrous;alloys (steels that cannot be hardened by heat treatment), the hardness and strength produced by mechanical or thermal treatment, or both, and characterized by a certain structure, mechanical properties. Or reduction of area during cold working. temper color.
A thin, tightly adhering oxide skin (only a few molecules thick) that forms when steel is tempered at a low temperature, or for a short time, in air or a mildly oxidizing atmosphere. The color, which ranges from straw to blue depending on the thickness of the oxide skin, varies with both tempering time and temperature. tempered martensite embrittlement
Embrittlement of ultrahigh-strength steels caused by tempering in the temperature range of 205 to 400 oC (400 to 750 oF); also called 350 oC or 500 oF embrittlement. Tempered martensite embrittlement is thought to result from the combined effects of cementite precipitation on prior-austenite grain boundaries or interlath boundaries and the segregation of impurities at prior-austenite grain boundaries. temper embrittlement
Embrittlement of alloy steels caused by holding within or cooling slowly through a temperature range just below the transformation range. Embrittlement is the result of the segregation at grain boundaries of impurities such as arsenic, antimony, phosphorus, and tin; it is usually manifested as an upward shift in ductile-to-brittle transition temperature. Temper embrittlement can be reversed by retempering above the critical temperature range, then cooling rapidly. tensile strength.
In tensile testing, the ratio of maximum load to original cross-sectional area. Also called ultimate tensile strength. tensile stress
A stress that causes two parts of an elastic body. on either side of a typical stress plane, to pull apart. Contrast with compressive stress. tension
The force or load that produces elongation.
terne
An alloy of lead containing 3 to l5% Sn, used as a hot dip coating for steel sheet or plate. Terne coatings, which are smooth and dull in appearance, give the steel better corrosion resistance and enhance its ability to be formed, soldered, or painted. therdermal electromotive force.
The electromotive force generated in a circuit containing two dissimilar metals when one junction is at a temperature different from that of the other. see also thermocouple. thermal embrittlement
Intergranular fracture of maraging steels with decreased toughness resulting from improper processing after hot working. Thermal embrittlement occurs upon heating above l095 oC (2000 oF ) and then slow cooling through the temperature range of 815 to 980 oC (1300 to l800 oF), and has been attributed to precipitation of titanium carbides and titanium carbonitrides at austenite grain boundaries during cooling through the critical temperature range.
thermally induced embrittlement See embrittlement.
thermal spraying
A group of coating or welding processes in which finely divided metallic or nonmetallic materials are deposited in a molten or semimolten condition to form a coating. The coating material may be in the form of powder, ceramic rod, wire, or molten materials. See also flame spraying and plasma spraying. thermocouple
A device for measuring temperatures, consisting of lengths of two dissimilar metals or alloys that are electrically joined at one end and connected to a voltage-measuring instrument at the other end. When one junction is hotter than the other, a thermal electromotive force is produced that is roughly proportional to the difference in temperature between the hot and cold junctions.
thermogalvanic corrosion
Corrosion resulting from an electrochemical cell caused by a thermal gradient. threshold stress
Threshold stress for stress-corrosion-cracking. The critical gross section stress at the onset of stress-corrosion cracking under specified conditions. throwing power.
(1) The relationship between the current density at a point on a surface and its distance from the counter electrode. The greater the ratio of the surface resistivity shown by the electrode reaction to the volume resistivity of the electrolyte, the better is the throwing power of the process. (2) The ability of a plating solution to produce a uniform metal distribution on an irregularly shaped cathode. Compare with covering power. tinning
Coating metal with a very thin layer of molten solder or brazing filler metal.
torsion
A twisting deformation of a solid body about an axis in which lines that were initially parallel to the axis become helices. torsional stress
The shear stress on a transverse cross section resulting from u twisting action. total carbon
The sum of the free carbon and combined carbon (including carbon in solution) in a ferrous alloy. toughness
The ability of a metal to absorb energy and deform plastically before fracturing. transcrystalline
See transgranular.
transcrystalline cracking See transgranular cracking. transference
The movement of ions through the electrolyte associated with the passage of the electric current. Also called transport or migration.
transgranular
Through or across crystals or grains. Also called intracrystalline or transcrystalline. transgranular cracking
Cracking or fracturing that occurs through or across a crystal or grain. Also called transcrystalline cracking. Contrast with intergranular cracking.
transgranular fracture
Fracture through or across the crystals or grains of a metal. Also called transcrystalline fracture or intracrystalline fracture. Contrast with intergranular fracture. transition metal
A metal in which the available electron energy levels are occupied in such away that the d-band contains less than its maximum number of ten electrons per atom, for example, iron, cobalt, nickel, and tungsten. The distinctive properties of the transition metals result from the incompletely filled d-levels. transition temperature
(1) An arbitrarily defined temperature that lies within the temperature range in which metal fracture characteristics (as usually determined by tests of notched specimens) change rapidly, such as from primarily fibrous (shear) to primarily crystalline (cleavage)
fracture. (2) Sometimes used to denote an arbitrarily defined temperature within a range in which the ductility changes rapidly with temperature. transpassive region
The region of an anodic polarization curve, noble to and; above the passive potential range, in which there is a significant increase in current density (increased metal dissolution) as the potential becomes more positive (noble). transpassive state
(1) State of anodically passivated metal characterized by a considerable increase of the corrosion current, in the; absence of pitting, when the potential is increased. (2) The noble region of potential where an electrode exhibits at higher than passive current density. triaxial stress
See principal stress (normal).
tuberculation
The formation of localized corrosion products scattered over the surface in the form of knoblike mounds called tubercles.
- U -
u-bend specimen
Horseshoe-shaped test piece used to detect the susceptibility of a material to stress corrosion cracking. ultimate strength
The maximum stress (tensile. compressive, or shear) a material can sustain without fracture, determined by dividing maximum load by the original cross-sectional area of the specimen. Also called nominal strength or maximum strength. underfilm corrosion
Corrosion that occurs under organic films in the form of randomly distributed threadlike filaments or spots. In many cases this is identical to filiform corrosion. uniaxial stress
See principal stress (normal). uniform corrosion
(1) A type of corrosion attack (deterioration) uniformly distributed over metal surface. (2) Corrosion that proceeds at approximately the same rate over a metal surface. Also called general corrosion.
- V -
vacuum deposition
Condensation of thin metal coatings on the cool surface of work in vacuum. valence
A positive number that characterizes the combining power of an element for other elements, as measured by the number of bonds to other atoms that one atom of the given element forms upon chemical combination: hydrogen is assigned valence 1, and
the valence is the number of hydrogen atoms, or their equivalent, with which an atom of the given element combines. vapor deposition
See chemical vapor deposition, physical vapor deposition and sputtering. vapor plating
Deposition of a metal or compound on a heated surface by reduction or decomposition of a volatile compound at a temperature below the melting points of the deposit and the base material. The reduction is usually accomplished by a gaseous reducing agent such as hydrogen. The decomposition process may involve thermal dissociation or reaction with the base material. Occasionally used to designate deposition on cold surfaces by vacuum evaporation. See also vacuum deposition. voids
A term generally applied to paints to describe holidays, holes, and skips in a film. Also used to describe shrinkage in castings and weld.
- W -
wash primer
A thin, inhibiting paint, usually chromate pigmented with a polyvinyl butyrate binder. weld cracking
Cracking that occurs in the weld metal. See also cold cracking, hot cracking, lamellar tearing, and stress-relief cracking. weld decay
Intergranular corrosion, usually of stainless steels or certain nickel-base alloys, that occurs as the result of sensitization in the heat-affected zone during the welding operation. wetting
A condition in which the interfacial tension between a liquid and a solid is such that the contact angle is 0o to 90o. wetting agent
A substance that reduces the surface tension of a liquid, thereby causing it to spread more readily on a solid surface. white liquor
Cooking liquor from the kraft pulping process produced by recausticizing green liquor with lime. white rust
Zinc oxide: the powdery product of corrosion of zinc or zinc-coated surfaces. work hardening
Same as strain hardening. working electrode
The test or specimen electrode in an electrochemical cell.
- Y -
yield
Evidence of plastic deformation in structural materials. Also called plastic flow or creep. See also flow. yield point
The first stress in a material, usually less than the maximum attainable stress, at which an increase in strain occurs without an increase in stress. Only certain metals - those that exhibit a localized, heterogeneous type of transition from elastic deformation to plastic deformation - produce a yield point. If there is a decrease in stress after yielding, a distinction may be made between upper and lower yield points. The load at which a sudden drop in the flow curve occurs is called the upper yield point. The constant load shown on the flow curve is the lower yield point. yield strength
The stress at which a material exhibits a specified deviation from proportionality of stress and strain. An onset of 0.2% is used for many metals.
yield stress
The stress level in a material at or above the yield strength but below the ultimate strength, i.e., a stress in the plastic range.
- Z -
zeta potential
See electrokinetic potential.
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