Appendix A

Glossary of Terms Used in Power Metallurgy

Absolute Pore Size - The maximum pore opening of a porous material, such as a filter through which no larger particle will pass. Synonymous with Maximum Pore Size.

Acicular Powder - Needle shaped particles.

Acrysol - A trademark for aqueous solutions of acrylic polymers.

Air Classification - The separation of powder into particle size fractions by means of an air stream of controlled velocity.

Alloy Powder - A powder all particles of which are composed of the same alloy of two or more metals. See Metal Powder.

Apparent Density - The weight of a unit volume of powder, usually expressed as grams per cubic centimeter, determined by a specified method.

Apparent Hardness - The value obtained by testing a sintered material with standard indentation hardness equipment. Since the reading is a composite of pores and solid material, it is usually lower than that of solid material of the same composition and condition. Not to be confused with particle hardness.

Arborescent Powder - See Dendritic Powder.

Atomization - The disintegration of a molten metal into particles by a rapidly moving gas or liquid stream or by mechanical means.

Atomized Metal Powder - Metal powder produced by the disintegration of a molten metal by a rapidly moving gas or liquid stream, of by mechanical means.

Average Pore Size - The average pore diameter of a porous material, such as a filter, which conforms to specific particle removal requirements, usually the removal of 95% to 100% of a given particle size distribution. Synonymous with Nominal Pore Size.

Binder - A cementing medium; either a material added to the powder to increase the green strength of the compact, and which is expelled during sintering; or a material (usually of relatively lower melting point) added to a powder mixture for the specific purpose of cementing together powder particles that alone would not sinter into a strong body.

Blank - A pressed, presintered or fully sintered compact, usually in the unfinished condition, requiring cutting, machining, or some other operation to give it its final shape. See Preforming.

Blending - The thorough intermingling of powders of the same nominal composition (not to be confused with mixing).

Bridging - The formation of arched cavities in a powder mass.

Briquet - See Compact.

Bulk Density - Synonymous with Apparent Density (U.S.), and Loading Weight (British).

Burn Off - That stage of a sintering cycle referring to the time and temperature necessary to remove ingredients used to assist the forming of a powder metallurgy part, such as binders or die lubricants.

Cake - A coalesced mass of unpressed metal powder.

Carbonyl Powder - A metal powder prepared by the thermal decomposition of a metal carbonyl.

Cement Copper - Copper precipitated by iron from copper sulfate solutions.

Chemically Precipitated Metal Powder - Powder produced by the replacement of one metal from a solution of its salts by the addition of another element higher in the electrochemical series, or by other reducing agent.

Classification - Separation of a powder into fractions according to particle size.

Coining - The pressing of a sintered compact to obtain a definite surface configuration (not to be confused with Repressing or Sizing).

Cold Pressing - The forming of a compact at room temperature.

Cold Welding - Cohesion between two surfaces of metal, generally under the influence of externally applied pressure at room temperature.

Compact - An object produced by the compression of metal powder, generally while confined in die, with or without the inclusion of nonmetallic constituents. Synonymous with Briquet.

Compacting Tool Set - See Die.

Composite Compact - A metal powder compact consisting of two or more adhering layers, rings, or other shapes of different metals or alloys with each layer retaining its original identity.

Compound Compact - A metal powder compact consisting of mixed metals, the particles of which are joined by pressing or sintering or both, with each metal particle retaining substantially its original composition.

Compressibility - A density ratio determined under definite testing conditions.

Compression Ratio-The ratio of the volume of the loose powder to the volume of the compact made from it. Synonymous with Fill Ratio.

Continuous Sintering - Presintering, or sintering, in such manner that the objects are advanced through the furnace at a fixed rate by manual or mechanical means. Synonymous with Stoking.

Core Rod - The separate member of the compacting tool set or die that forms a hole in the compact.

Cored Bar - A compact of bar shape heated by its own electrical resistance to a temperature high enough to melt its interior.

Cracked Ammonia - See Dissociated Ammonia.

Cut-See Fraction.

Dendritic Powder - Particles, usually of electrolytic origin, having the typical pine tree structure. Synonymous with Arborescent Powder.

Density (Dry) - The weight per unit volume of an unimpregnated P/M part.

Density (Wet) - The weight per unit volume of a P/M part impregnated with oil or other nonmetallic materials.

Density Ratio - The ratio of the determined density of a compact to the absolute density of metal of the same composition, usually expressed as a percentage.

Die - The part or parts making up the confining form in which a powder is pressed. The parts of the die may be some or all of the following: Die body, punches, and core rods. Synonymous with Mold and Compacting Tool Set.

Die Body - The Stationary or fixed part of a die.

Die Insert - A removable liner or part of a die body or punch. Synonymous with Die Liner.

Die Liner - See Die Insert.

Die Lubricant - A lubricant mixed with the powder or applied to the walls of the die and punches to facilitate the pressing and ejection of the compact.

Die Set - The parts of a press that hold and locate the die in proper relation to the punches.

Dissociated Ammonia - A reducing gas produced by the thermal decomposition of anhydrous ammonia over a catalyst, resulting in a gas of 75% hydrogen and 25% nitrogen. Synonymous with Cracked Ammonia.

Disintegration - The reduction of massive material to powder.

Electrolytic Powder - Powder produced by electrolytic deposition or the pulverization of an electrodeposit.

Endothermic Atmosphere (Gas) - A reducing gas atmosphere used in sintering and produced by the reaction of a hydrocarbon fuel gas and air over a catalyst with the aid of an external heat source. It is low in carbon dioxide and water vapor with relatively large percentages of hydrogen and carbon monoxide. Maximum combustibles approximately 60%.

Equiaxed Powder - See Granular Powder.

Exothermic Atmosphere (Gas) - A reducing gas atmosphere used in sintering and produced by partial or complete combustion of a hydrocarbon fuel gas and air. Maximum combustibles approximately 25%.

Exudation - The action by which all or a portion of the low melting constituent of a compact is forced to the surface during sintering. Sometimes referred to as "bleed out". Synonymous with Sweating.

Fill Ratio - See Compression Ratio.

Fines - The portion of a powder composed of particles which are smaller than a specified size, currently less than 44 microns. See also Superfines.

Flake Powder - Flat or scale-like particles whose thickness is small compared with the other dimensions.

Flow Rate - The time required for a powder sample of standard weight to flow through an orifice in a standard instrument according to a specified procedure.

Fraction - That portion of a powder sample which lies between two stated particle sizes. Synonymous with Cut.

Gas Classification - The separation of powder into particle size fractions by means of a gas stream of controlled velocity.

Granular Powder - Particles having approximately equidimensional nonspherical shapes.

Granulation - The production of coarse metal particles by pouring the molten metal through a screen into water (shotting) or by violent agitation of the molten metal while solidifying. Not to be confused with Granulation as used in pharmaceutical terminology.

Green - Unsintered (not sintered); for example: green compact, green density, green strength.

Growth - An increase in dimensions of a compact which may occur during sintering (converse of Shrinkage).

Hall Paste Process - A ball milling process for powder production in which a liquid hydrocarbon is used as a suspension medium.

Hametag Process - A ball milling method of powder production in which an inert gas atmosphere is used to prevent oxidation of the powder.

Hot Pressing - The simultaneous heating and molding of a compact.

Hydrogen Loss - The loss in weight of metal powder or of a compact caused by heating a representative sample for a specified time and temperature in a purified hydrogen atmosphere—broadly a measure of the oxygen content of the sample, when applied to materials containing only such oxides as are reducible with hydrogen and no hydride forming material.

Hydrogen-Reduced Powder - Powder produced by the hydrogen reduction of a metal oxide.

Impregnation - A process of filling the pores of a sintered compact with a nonmetallic material such as oil, wax or resin.

Infiltration - A process of filling the pores of a sintered, or unsintered, P/M compact with a metal or alloy of lower melting point.

Interconnected Porosity - A network of contiguous pores in and extending to the surface of a sintered compact. Usually applied to P/M materials where the interconnected porosity is determined by impregnating the specimens with oil.

Irregular Powder - Particles lacking symmetry.

K-factor - The strength constant in the formula for radial crushing strength of a plain sleeve specimen of sintered metal. See Radial Crushing Strength.

Lamination - A rupture in the pressed compact caused by the mass slippage of a part of the compact. Synonymous with Pressing Crack and Slip Crack.

Leafing - Formation of a continuous film of metal through surface tension; the higher the surface tension, the more rapid and complete is the leafing.

Liquid Phase Sintering - Sintering of a P/M compact, or loose powder aggregate under conditions where a liquid phase is present during part of the sintering cycle.

Loading - The filling of the die cavity with powder.

Lower Punch - The member of the compacting tool set or die that determines the volume of powder fill and forms the bottom of the part being produced. Secondary or subdivided lower punches may be necessary to facilitate filling, forming and ejecting of multiple-level parts.

Lubricating - Mixing with, or incorporating in, a powder some agent to facilitate pressing and ejecting the compact from the die body; applying a lubricant to the die walls and punch surfaces.

Matrix Metal - The continuous phase of a polyphase alloy or mechanical mixture; the physically continuous metallic constituent in which separate particles of another constituent are embedded.

Maximum Pore Size - See Absolute Pore Size.

Mechanical Component - A shaped body pressed from metal powder and sintered wherein self-lubrication is not a primary property. A part but not an oil-impregnated bearing. See Powder Metallurgy Part.

Mesh - The sieve number of the finest screen through which substantially all of the particles of a given sample will pass. The number of screen openings per linear inch of screen.

Metal Filter - A metal structure having controlled interconnected porosity produced to meet filtration or permeability requirements.

Metal Powder - Discrete particles of elemental metals or alloys normally within the size range of 0.1 to 1000 microns.

Milling - The mechanical treatment of metal powder, or metal powder mixtures, as in a ball mill, to alter the size or shape of the individual particles, or to coat one component of the mixture with another.

Minus Sieve - The portion of a powder sample which passes through a standard sieve of specified number. See Plus Sieve.

Mixing - The thorough intermingling of powders of two or more materials.

Mold - See Die.

Molding - The pressing of powder to form a compact.

Needles - Elongated rod-like particles.

Nodular Powder - Irregular particles having knotted, rounded, or similar shapes.

Oversize Powder - Particles coarser than the maximum permitted by a given particle-size specification.

Packing Material - Any material in which compacts are embedded during the presintering or sintering operation.

Particle Size - The controlling lineal dimension of an individual particle as determined by analysis with sieves or other suitable means.

Particle-Size Distribution - The percentage by weight, or by number, of each fraction into which a powder sample has been classified with respect to sieve number or microns. (Preferred usage: "Particle-size distribution by weight" or "particle-size distribution by frequency.")

Permeability - A property measured as the rate of passage of a liquid or gas through a compact; measured under specified conditions.

Plates - Flat particles of metal powder having considerable thickness.

Plus Sieve - The portion of a powder sample retained on a standard sieve of specified number. See Minus Sieve.

P/M - The acronym representing powder metallurgy. Used as P/M part, P/M product, P/M process, etc.

P/M Part - A shaped object that has been formed from metal powders and bonded by heating below the melting point of the major constituent. A structural or mechanical component, bearing or bushing made by the powder metallurgy process.

Polishing - An operation in which flake powder and a small quantity of lubricant are rotated in a cylinder to cause the particles to rub against each other, thus smoothing the surfaces. The lubricant imparts leafing qualities to the powder.

Pore-Forming Material - A substance included in a powder mixture which volatizes during sintering and, thereby, produces a desired kind and degree of porosity in the finished compact.

Porosity - The amount of pores (voids) expressed as a percentage of the total volume of the powder metallurgy part.

Porous Metal - A metal structure having controlled interconnected porosity. See Metal Filter.

Powder Flow Meter - An instrument for measuring the rate of flow of a powder according to a specified procedure.

Powder Lubricant - An agent mixed with or incorporated in a powder to facilitate the pressing and ejecting of the compact.

Powder Metallurgy - The arts of producing metal powders and of the utilization of metal powders for the production of massive materials and shaped objects.

Powder Metallurgy Part - See P/M Part.

Powder Rolling - The progressive compacting of metal powders by the use of a rolling mill. Synonymous with Roll Compacting.

Pre-alloyed Powder - An alloy in powder form in which each particle is of the same composition.

Preforming - The initial pressing of a metal powder to form a compact which is subjected to a subsequent pressing operation other than coining or sizing. Also, the preliminary shaping of a refractory metal compact after presintering and before the final sintering.

Premix - A uniform intermingling of powders of two or more materials performed by the powder producer (not to be confused with preblending - See Blending).

Presintering - The heating of a compact at a temperature below the normal final sintering temperature, usually to increase the ease of handling or shaping the compact, or to remove a lubricant or binder prior to sintering.

Pressed Bar - A compact in the form of a bar; a green compact.

Pressed Density - The weight per unit volume of an unsintered compact. Synonymous with Green Density.

Pressing Crack - See Lamination.

Puffed Compact - A compact expanded by internal gas pressure.

Pulverization - The reduction in particle size of metal powder by mechanical means; a specific type of Disintegration.

Punch - Part of a die or compacting tool set which is used to transmit pressure to the powder in the die cavity. See Upper Punch and Lower Punch.

Radial Crushing Strength - The relative capacity, of a plain sieve specimen made by powder metallurgy, to resist fracture induced by a force applied between flat parallel plates in a direction perpendicular to the axis of the specimen.

Rate-of-Oil-Flow - The rate at which a specified oil will pass through a sintered porous compact under specified test conditions.

Reduced Metal Powder - Metal powder produced, without melting, by the chemical reduction of metal oxides or other compounds.

Repressing - The application of pressure to a previously pressed and sintered compact, usually for the purpose of improving some physical property.

Roll Compacting - See Powder Rolling.

Rolled Compact - A compact made by passing metal powder continuously through a rolling mill so as to form relatively long sheets of pressed material.

Rotary Press - A machine fitted with a rotating table carrying multiple dies in which a material is pressed.

Screen Analysis - See Sieve Analysis.

Segment Die - A die made of parts which can be separated for the ready removal of the compact. Synonymous with Split Die.

Shrinkage - A decrease in dimensions of a compact which may occur during sintering (converse of Growth).

Sieve Analysis - Particle size distribution; usually expressed as the weight percentage retained upon each of a series of standard sieves of decreasing size and the percentage passed by the sieve of finest size. Synonymous with Screen Analysis.

Sieve Classification - The separation of powder into particle-size ranges by the use of a series of graded sieves.

Sieve Fraction - That portion of a powder sample which passes through a standard sieve of specified number and is retained by some finer sieve of specified number.

Sintering - Bonding of particles in a mass of metal powder by molecular (or atomic) attraction in the solid state, through the application of heat, causing strengthening of the powder mass and normally resulting in densification and recrystallization due to material transport. Sintering (Noun)-See P/M Part.

Sizing - A final pressing of a sintered compact to secure desired size.

Slip Casting - A method of forming metal shapes by pouring a stabilized water suspension of metal powders into the shaped cavity of a fluid-absorbing mold, diffusing the liquid into the mold wall, removing the casting from the mold and sintering.

Slip Crack - See Lamination.

Specific Surface - The surface area of one gram of powder, usually expressed in square centimeters.

Spherical Powder - Globular shaped particles.

Split Die - See Segment Die.

Spongy - A porous condition in metal powder particles usually observed in reduced oxides.

Stoking - See Continuous Sintering.

Stripper Punch - A punch, which in addition to forming the top or bottom of the die cavity, later moves further into the die to eject the compact.

Subsieve Fraction - Particles all of which will pass through a 44 micron (No. 325) standard sieve.

Superfines - The portion of a powder composed of particles that are smaller than a specified size, currently less than 10 microns.

Sweating - See Exudation.

Tap Density - The apparent density of a powder obtained when the receptacle is tapped or vibrated during loading under specified conditions.

Transverse Rupture Strength - The stress, calculated from the flexure formula, required to break a specimen as a simple beam supported near the ends and applying the load midway between the fixed center line of the supports.

Upper Punch - The member of the compacting tool set or die that closes the die and forms the top of the part being produced.

Warpage - Distortion which may occur in a compact during sintering.