structure. An ordered structure of titanium-aluminum compound with a

stoi-chiometry of Ti₃Al.

annealed powder. A powder that is heat treated to render it soft and compactible.

annealing. A generic term denoting a treat-ment, consisting of heating to, and holding at, a suitable temperature followed by

cool-ing at a suitable rate. It is used primarily to soften metallic materials but also to simulta-neously produce desired changes in other properties or in microstructure. The purpose of such changes may be, but is not confined to: improvement of machinability, facilita-tion of cold work, improvement of mechani-cal or electrimechani-cal properties, and/or increase in stability of dimensions. When the term is used without qualification, full annealing is implied. When applied only for the relief of stress, the process is properly called stress relieving or stress-relief annealing. In non-ferrous alloys, annealing cycles are designed to: (1) remove part or all of the effects of cold working (recrystallization may or may not be involved); (2) cause substantially complete coalescence of precipitates from solid solution in relatively coarse form; or (3) both, depending on composition and ma-terial condition. Specific process names in commercial use are final annealing, full nealing, intermediate annealing, partial an-nealing, recrystallization anan-nealing, stress-relief annealing, and anneal to temper. See alsomultiple annealing.

atm. Atmosphere (pressure).

atomic number. The number of protons in an atomic nucleus; determines the individuality of the atom as a chemical element.

atomic percent. The number of atoms of an el-ement in a total of 100 representative atoms of a substance.

atomization. The disintegration of a molten metal into particles by a rapidly moving gas or liquid stream or by other means.

AWG. American wire gage.

AWS. American Welding Society.

B

B. Bar.

bake. (verb). To remove gases from a powder at low temperatures.

banded structure. A segregated structure con-sisting of alternating, nearly parallel bands of Titanium: A Technical Guide

Matthew J. Donachie, Jr., p333-343 DOI:10.1361/tatg2000p333

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different composition, typically aligned in the direction of primary hot working.

B&S. Brown and Sharpe (gage).

bar. A metal product of uniform section pro-duced in short to moderate lengths by roll-ing, extrusion, or other processes such as swaging or powder metallurgy. Section shapes generally are symmetrical and circu-lar, rectangucircu-lar, or hexagonal in form, but other shapes are produced. Bars are rela-tively smaller in cross-sectional dimensions than billets but are substantially larger than wire. Bar may be used for forging stock, wire drawing stock, or for the production of items by machining.

barstock. Same as bar.

basal plane. A plane perpendicular to the prin-cipal axis (c axis) in a tetragonal or hexago-nal structure.

basketweave. Alpha platelets with or without interleavedβ platelets that occur in colonies in a Widmanstätten structure.

batch. The total output of one mixing of pow-der metal; sometimes called a lot.

batch sintering. Presintering or sintering in such a manner that compacts are sintered and removed from the furnace before additional unsintered compacts are placed in the fur-nace.

Bauschinger effect. For both single-crystal and polycrystalline metals, any change in stress-strain characteristics that can be as-cribed to changes in the microscopic stress distribution within the metal, as distin-guished from changes caused by strain hard-ening. In the narrow sense, the process whereby plastic deformation in one direction causes a reduction in yield strength when stress is applied in the opposite direction.

beta (β). The high-temperature allotrope of ti-tanium with a body-centered cubic crystal structure that occurs above theβ transus.

beta eutectoid stabilizer. An alloying element that dissolves preferentially in the β phase, lowers theα-β to β transformation tempera-ture, and results inβ decomposition to α plus a compound.

beta fleck. Alpha-lean region in the α-β microstructure significantly larger than the primary α width. This β-rich area has a β transus measurably below that of the matrix.

Beta flecks have reduced amounts of primary α, which may exhibit a morphology different from the primary α in the surrounding α-β matrix.

beta isomorphous stabilizer. An alloying ele-ment that dissolves preferentially in the β phase, lowers the α-β to β transformation temperature without a eutectoid reaction, and forms a continuous series of solid solutions with,β-titanium.

beta-STOA. Beta solution overaging. See also solution heat treatment and overaging.

beta transus. The minimum temperature above which equilibrium α does not exist. For β eutectoid additions, the β transus ordinarily is applied to hypoeutectoid compositions or

those that lie to the left of the eutectoid com-position.

billet. (1) A solid, semifinished round or square product that has been hot worked by forging, rolling, or extrusion; usually smaller than a bloom. (2) A general term for wrought start-ing stock used in makstart-ing forgstart-ings or extru-sions.

binder. A substance added to the powder to:

(a) increase the strength of the compact; and (b) cement together powder particles that alone would not sinter into a strong object.

blank. A pressed, presintered, or fully sintered compact, usually in the unfinished condition, to be machined or otherwise processed to fi-nal shape or condition.

body-centered cubic lattice structure. A unit cell that consists of atoms arranged at cube corners with one atom at the center of the cube.

braze. A joint produced by heating an assem-bly to suitable temperatures and by using a filler metal having a liquidus above 450°C (840 °F) and below the solidus of the base metal. The filler metal is distributed between the closely fitted faying surfaces of the joint by capillary action.

brazeability. The capacity of a metal to be brazed, under the fabrication conditions im-posed, into a specific suitably designed structure and to perform satisfactorily in the intended service.

braze welding. A method of welding by using a filler metal having a liquidus above 450°C (840 °F) and below the solidus of the base metals. Unlike brazing, in braze welding the filler metal is not distributed in the joint by capillary attraction.

brazing. A group of processes that join solid materials together by heating them to a suit-able temperature and by using a filler metal having a liquidus above approximately 450

°C (840 °F) and below the solidus of the base materials. The filler metal is distributed be-tween the closely fitted surfaces of the joint by capillary attraction.

brazing filler metal. A nonferrous filler metal used in brazing and braze welding.

Brinell hardness number (HB). A number re-lated to the applied load and to the surface area of the permanent impression made by a ball indenter.

Brinell hardness test. A test for determining the hardness of a material by forcing a hard steel or carbide ball of specified diameter into it under a specific load. The result is ex-pressed as the Brinell hardness number, which is the value obtained by dividing the applied load in kilograms by the surface area of the resulting impression in square milli-meters.

brittle. Permitting little or no plastic (perma-nent) deformation prior to fracture.

brittle fracture. Separation of a solid accom-panied by little or no macroscopic plastic de-formation. Typically, brittle fracture occurs by rapid crack propagation with less expen-diture of energy than for ductile fracture.

brittleness. The tendency of a material to frac-ture without first undergoing significant plastic deformation. Contrast withductility.

C

cake. A coalesced mass of unpressed metal powder.

CAP. Seeconsolidation by atmospheric pres-sure.

carbonitriding. Acase 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 car-bon and nitrogen by the surface and, by dif-fusion, create a concentration gradient. The heat-treating process is completed by cooling at a rate that produces the desired properties in the workpiece.

carburizing. Absorption and diffusion of car-bon into solid ferrous alloys by heating, to a temperature usually above Ac₃, in contact with a suitable carbonaceous material. A formof case hardening that produces a car-bon gradient extending inward from the sur-face, enabling the surface layer to be hard-ened either by quenching directly from the carburizing temperature or by cooling to room temperature, then reaustenitizing and quenching.

case hardening. A generic term covering sev-eral 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 processes com-monly used are carburizing and quench hardening, cyaniding, nitriding, and carbonitriding. The use of the applicable specific process name is preferred.

cast or casting. To fabricate an item by pour-ing molten metal into a shaped cavity and permitting the metal to solidify. A cast can relate to the item or may be a synonym for heat, that is an identifiable chemistry lot.

CAW-G. Seegas carbon arc welding.

Charpy test. An impact test in which a V-notched, keyhole-notched, or U-notched specimen, supported at both ends, is struck behind the notch by a striker mounted at the lower end of a bar that can swing as a pendu-lum. The energy that is absorbed in fracture is calculated at the height to which the striker would have risen had there been no specimen and the height to which it actually rises after fracture of the specimen.

chemical vapor deposition (CVD). The pre-cipitation of a metal from a gaseous com-pound onto a solid or particulate substrate.

CHIP. CIP plus sinter plus HIP. A 3-stage P/M process. See alsoCIP.

CHM. Chemical milling, a machining tech-nique.

CIP. Seecold isostatic pressing.

334 / Titanium: A Technical Guide

close-packed. A geometric arrangement in which a collection of equally sized spheres (atoms) may be packed together in a mini-mum total volume.

coarse grains. Grains larger than normal for the particular wrought metal or alloy or of a size that produces a surface roughening known as orange peel or alligator skin in wrought alloys.

cold isostatic pressing. Forming technique in which high fluid pressure is applied to a powder (metal or ceramic) part at ambient temperature. Water or oil is used as the pres-sure medium.

cold pressing. The forming of a compact from powder at, or below, room temperature.

cold-worked structure. A microstructure re-sulting from plastic deformation of a metal or alloy below its recrystallization tempera-ture.

cold working. Deforming metal plastically un-der conditions of temperature and strain rate that induce strain hardening. Usually, but not necessarily, conducted at room temperature.

Contrast withhot working.

colonies. Regions within prior beta grains with alpha platelets having nearly identical orien-tations. In commercially pure titanium, colo-nies often have serrated boundaries. Col-onies arise as transformation products during cooling from the beta fields at cooling rates that induce platelet nucleation and growth.

compact. An object produced by the compres-sion of metal powder, generally while con-fined in a die, with or without the inclusion of nonmetallic constituents.

compact, compacting, compaction. The oper-ation or process of producing a compact;

sometimes called pressing.

consolidation by atmospheric pressure (CAP).

A P/M consolidation process wherin the ap-plied pressure comes from the atmosphere.

consumable electrode. A general term for any arc welding electrode made chiefly of filler metal.

consumable electrode remelting. A process for refining metals in which an electric cur-rent passes between an electrode made of the metal to be refined.

corrosion. The deterioration of a metal by a chemical or electrochemical reaction with its environment.

corrosion embrittlement. The severe loss of ductility of a metal resulting from corrosive attack, usually intergranular and often not vi-sually apparent.

corrosion fatigue. Cracking produced by the combined action of repeated or fluctuating stress and a corrosive environment at lower stress levels or fewer cycles than would be required in the absence of a corrosive envi-ronment.

corrosive wear. Wear in which chemical or electrochemical reaction with the environ-ment is significant.

cph. Close-packed hexagonal. Seehexagonal close-packed lattice structure.

creep. Time-dependent strain occurring under stress usually at elevated temperatures. The creep strain occurring at a diminishing rate is called primary, or transient, creep; that oc-curring at a minimum and almost constant rate, secondary, or steady-rate creep; that oc-curring at an accelerating rate, tertiary creep.

These rates are frequently represented graph-ically as 1, 2, and 3, or as I, II, and III.

creep limit. (1) The maximum stress that will cause less than a specified quantity of creep in a given time. (2) The maximum nominal stress under which the creep strain rate de-creases continuously with time under constant load and at constant temperature. Sometimes used synonymously with creep strength.

creep rate. The slope of the creep-time curve at a given time determined from a Cartesian plot.

creep recovery. Time-dependent strain after release of load in a creep test.

creep rupture strength. The stress that will cause fracture in a creep test at a given time in a specified constant environment. Also known as stress-rupture strength.

creep rupture test. Same as stress-rupture test.

creep strain. The time-dependent total strain (extension plus initial gage length) produced by applied stress during a creep test.

creep strength. The stress that will cause a given creep strain in a creep test at a given time in a specified constant environment.

creep stress. The constant load divided by the original cross-sectional area of the specimen.

crevice corrosion. A type of concentration cell corrosion; corrosion caused by the concen-tration or depletion of dissolved salts, metal ions, oxygen, or other gases, and such, in crevices or pockets remote from the principal fluid stream, with a resultant building up of differential cells that ultimately cause deep pitting. Localized corrosion of a metal sur-face at, or immediately adjacent to, an area that is shielded from full exposure to the en-vironment because of close proximity be-tween the metal and the surface of another material.

critical stress intensity factor (K_Ic). A mea-sure of fracture toughness. Increased K_Ic in-dicates greater resistance to fracture. K_Icis a common means, but not the only one, of de-scribing quantitatively the fracture resistance of an alloy. Stress intensity factors vary with loading conditions. The I refers to the load-ing condition (i.e. plane strain). The c refers to critical condition, above which the stress (load) need no longer be increased to cause fracture. K_Ic varies with material chemistry and processing history. It is a function of temperature and generally decreases as tem-perature decreases.

crystal. A solid composed of atoms, ions, or molecules arranged in a pattern that is peri-odic in three dimensions.

crystallization. (1) The separation, usually from a liquid phase on cooling, of a solid crystalline phase.(2) Sometimes erroneously

used to explain fracturing that actually has occurred by fatigue.

curing. The processing of a mold to obtain de-sired characteristics.

CVD. Seechemical vapor deposition.

cyaniding. Acase hardening process in which a ferrous material is heated above the lower transformation temperature range in a molten salt containing cyanide to cause simulta-neous absorption of carbon and nitrogen at the surface and, by diffusion, create a con-centration gradient.Quench hardening com-pletes the process.

D

DA. Seeduplex annealing.

da/dN. Seefatigue crack growth rate.

DBTT. Ductile-to-brittle transition temperature.

deformation. A change in the form of a body due to stress, thermal change, change in moisture, or other causes. Measured in units of length.

descaling. Removing the thick layer of oxides formed on some metals at elevated tempera-tures.

DFB. Seediffusion brazing.

DFW. Seediffusion welding.

diam. Diameter.

diffusion brazing (DFB). A brazing process that joins two or more components by heat-ing them to suitable temperatures and by us-ing a filler metal or an in situ liquid phase.

The filler metal may be distributed by capil-lary attraction or may be placed or formed at the faying surfaces. The filler metal is dif-fused with the base metal to the extent that the joint properties have been changed to ap-proach those of the base metal. Pressure may or may not be applied.

diffusion welding (DFW). A high-tempera-ture, solid-state welding process that perma-nently joins faying surfaces by the simulta-neous application of pressure and heat. The process does not involve macroscopic defor-mation, melting, nor relative motion of parts.

A solid filler metal (diffusion aid) may or may not be inserted between the faying sur-faces.

double aging. Employment of two different ag-ing treatments to control the type of precipi-tate formed from a supersaturated matrix in order to obtain the desired properties. The first aging treatment, sometimes referred to as intermediate or stabilizing, is usually car-ried out at higher temperature than the sec-ond.

ductile fracture. Fracture characterized by tearing of metal accompanied by appreciable gross plastic deformation and expenditure of considerable energy.

ductility. The ability of a material to deform plastically before fracturing. Measured by elongation or reduction of area in a tension test, by height of cupping in a cupping test, or by the radius or angle of bend in a bend Glossary / 335

test. Contrast withbrittleness; see also plas-tic deformation.

duplex annealing (DA). Seemultiple annealing.

duplexing. Any two-furnace melting or refin-ing process. Also called duplex meltrefin-ing or duplex processing.

E

EBC. Seeelectron beam cutting.

EBW. Seeelectron beam welding.

ECM. Electrochemical machining.

electrode. (1) The isolated sponge, master al-loy, and/or revert used in consumable vac-uum arc melting. (2) The solidified ingot in cases when it is to be remelted again in dou-ble and triple melting operations.

electron beam cutting (EBC). A cutting pro-cess that uses the heat obtained from a con-centrated beam composed primarily of high-velocity electrons that impinge upon the workpieces to be cut; it may or may not use an externally supplied gas.

electron beam welding (EBW). A welding process that produces coalescence of metals with the heat obtained from a concentrated beam composed primarily of high-velocity electrons impinging upon the surfaces to be joined.

ELI. Extra-low interstitial.

elongated alpha. A fibrous type of structure brought about by unidirectional metalwork-ing. It may be enhanced by the prior presence of blocky and/or grain boundary alpha.

elongated grain. A grain with one principal axis significantly longer than either of the other two.

elongation. A term used in mechanical testing to describe the amount of extension of a test piece when stressed. In tensile testing, the in-crease in the gage length, measured after fracture of the specimen within the gage length, usually expressed as a percentage of the original gage length.

embrittlement. The severe loss of ductility and/or toughness of a material, usually a metal or alloy.

endurance limit. The maximum stress below which a material can presumably endure an infinite number of stress cycles. If the stress is not completely reversed, the value of the mean stress, the minimum stress, or the stress ratio also should be stated. Compare withfatigue limit.

epitaxial. Having orientation controlled by the crystal substrate; use of crystals and of the relation between them and their substrate.

epitaxy. Growth of an electrodeposit or vapor deposit in which the orientation of the tals in the deposit are directly related to

epitaxy. Growth of an electrodeposit or vapor deposit in which the orientation of the tals in the deposit are directly related to

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