Powder Blending/Mixing Compacting

Sintering

Powder Metallurgy (P/M)

Particulate Processing of Metals and Ceramics

Powder Metallurgy (P/M)

The Characterization of EngineeringPowders

Production of Metallic Powders Conventional Pressing and Sintering Alternative Pressing and Sintering

Techniques Materials and Products for P/M

Powder Metallurgy (P/M) ?Metal processing technology in which parts

are produced from metallic powders• Usual PM production sequence:

Pressing - powders are compressed into desired shapeto produce green compact• Accomplished in press using punch-and-die

tooling designed for the partSintering – green compacts are heated to bond the

particles into a hard, rigid mass• Performed at temperatures below the melting

point of the metal

Why Powder Metallurgy isImportant ?

• P/M parts can be mass produced to netshape or near net shape, eliminating orreducing the need for subsequentmachining

• P/M process wastes very little material - ~97% of starting powders are converted toproduct

• P/M parts can be made with a specifiedlevel of porosity, to produce porous metalparts– Examples: filters, oil‑impregnated bearings and gears

Illustration

Incandescent bulbs

windshield penetrator sabot stabilizing fin propellant

Kinetic Energy PenetratormaterialsTungsten Heavy Alloy (WHA) Typical composition (wt.%): 90W-7Ni-3Fe Liquid Phase sintered 1500°C melting point of binder alloy (Ni-Fe) ~1465°Crequirements• high density• dimensional precision

Kinetic Energy Armour Piercing Penetrator

P/M for Automobiles

P/M Connecting Rods

Gears

Medical Radiation Shielding

Tungsten Heavy Alloy

Cutting tool inserts

Earlier, high speed steel (HSS) which was manufactured by casting route was used for cutting applications. Such steels are called cutting tool steels. However, they cannot be used by cutting at high speeds wherein the temperature can exceed 600°C. For still higher cutting output, hardmetals or cemented carbides [WC-(6-10 wt.%)Co] is used. Such alloys are consolidated by liquid phase sintering.

P/M Work Materials

• Mostly used for bulk ceramic components• Other P/M metals include copper, nickel,

and refractory metals such asmolybdenum and tungsten

• Metallic carbides such as tungsten carbideare often included within the scope ofpowder metallurgy

Engineering Powders

A powder can be defined as a finely dividedparticulate solid

• Engineering powders include metals andceramics

• Geometric features of engineeringpowders:– Particle size and distribution– Particle shape and internal structure– Surface area

Milled Ti Powder

Electrolytic Cu Powder

Screen Mesh

!

PS =1

MC" tw

Particle Shapes in PM

Inter-particle Friction and FlowCharacteristics

Angle of Repose

Inter-particle Friction and FlowCharacteristics

Production of MetallicPowders

• In general, producers of metallic powdersare not the same companies as those thatmake PM parts

• Any metal can be made into powder form• Three principal methods by which metallic

powders are commercially produced1. Atomization2. Chemical3. Electrolytic

• In addition, mechanical methods areoccasionally used to reduce powder sizes

High velocity gas stream flows throughexpansion nozzle, siphoning molten metal frombelow and spraying it into container

Gas Atomization Method

Iron Powders for P/M

50 µm