pt7

hot isostatic pressing (HIP)

a compaction process in which (1) a metal powder is placed in a mold made of high-melting-point sheet steel, (2) the assembly is pressurized in a chamber containing argon or another inert gas for an extended time under high temperatures, and (3) the assembly is removed; this process yields parts of very high quality but is costly and time consuming, so it is reserved mainly for expensive parts such as for the final densification of cutting tools and tool steels and for superalloy components for the aircraft and aerospace industries and in military, medical, and chemical applications

powder (metal) injection molding (PIM)

a compaction process in which (1) very fine metal powders are blended with a 25 to 45% polymer of a wax-based binder, (2) the mixture is forced into a die cavity under pressure (like in die casting) at a temperature of 135 to 200 deg celsius, (3) the plastic/binder is removed by burning off or solvent extraction, and (4) the resulting parts are sintered in a furnace

green compact

a workpiece that has undergone the first three steps of the powder metallurgy process but not steps 4 or 5

pressureless compaction

compaction process in which a die is gravity filed with metal powder and the powder is sintered directly in the die; it produces the low-density metal parts

spray deposition

compaction process in which the atomized metal is sprayed over a rotation mandrel to produce seamless tubing and pipe

powder rolling (roll compaction)

compaction process that involves the feeding of a metal powder into the roll gap in a two-high rolling mill in order to produce a continuous strop at speeds up to 0.5 meters/sec; this can be used to make sheet metal for electrical components and coins

debinding

powder injection molding sub-process in which parts are placed in low-temperature oven to burn off the plastic prior to sintering

infiltration

powder metallurgy process performed after sintering in which (1) a slug of a lower-melting-point metal is placed in contact with a sintered part, (2) the resulting assembly is heated to a temperature high enough to melt the slug, and (3) the molten metal infiltrates the pores of the sintered part by capillary action; it produces a relatively pore-free part having good density and strength and better hardness that the sintered part alone

hydrostatic pressure

pressure exerted by a fluid at equilibrium at a given point within the fluid due to gravity

powder production

step 1 in the powder metallurgy process

blending

step 2 in the powder metallurgy process in which blended powders are formed into various shapes using mechanical or hydraulic press, isostatic pressure systems, injection molding systems, or other means; in this step, the goal is to produce parts of the required shape, density, and particle-to-particle contact so they are sufficiently strong to undergo further processing

compaction

step 3 in the powder metallurgy process in which blended powders are formed into various shapes using mechanical or hydraulic presses, isostatic pressure systems, injection molding systems, or other means; in this step, the goal is to produce parts of the required shape, density, and particle-to-particle contact so they are sufficiently strong to undergo further processing

sintering

step 4 in the powder metallurgy process in which the green compacts are heated in a controlled atmosphere furnace to a temperature below the melting point, but sufficiently high to allow bonding (fusion) of the individual particles

finishing operations

step 5 in the powder metallurgy process in which a part produced by powder metallurgy is forged, machined, ground, plated, heat treated, and/or electoplated

impregnating

the adding of fluid to a part after it has been sintered in order to take advantage of the part's porosity and produce a finished part with special properties (e.g. a part that does not need to be greased)

powder metallurgy

the compacting of metal powders into desired and often complex shapes and subsequent heating without melting to form a solid piece; it is often useful for making part form high-melting point refractory metals and other parts that may be uneconomical to produce by other methods

powder forging

the forging of workpieces that have been produced by powder metallurgy (for example the isothermal forging of jet engine parts using molybdenum dies at ATI ladish)

vapor-phase transport

the formation of bonds between adjacent powder particles during sintering that results from the movement of atoms in a gaseous state across the interface

diffusion (solid state) bonding

the formation of bonds between adjacent powder particles during sintering that results from the movement of atoms in a solid state across the interface

liquid-phase sintering

the formation of bonds between adjacent powder particles during sintering that results from the movement of atoms in the liquid state across the interface

continuous sintering furnace

the most common sintering furnace that consists of (1) a burn-off chamber where lubricants in the green compacts volatilized to improve bond strength and prevent cracking, (2) a high temperature chamber for sintering, and (3) a cooling chamber; parts move on a continuous conveyer through these three chambers

atomization

the spraying of a jet of water or air on a stream of liquid metal that is being poured in order to produce a metal powder

green strength

the strength of a workpiece that has undergone the first three steps of the powder metallurgy process but not steps 4 or 5; it is typically much less than that of a part produced by casting or forging

cold isostatic pressing (CIP)

a compaction process in which (1) a metal powder is placed in a flexible rubber mold, (2) the assembly is pressurized hydrostatically in a chamber for an extended time, usually using water, and (3) the assembly is removed; the process achieves more uniform compaction than a press