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UNIT-IV Processing of Metal powders,
Ceramics and Glasses
Powder Metallurgy
• producing metal or alloy powders, and using them to make finished or semi-finished products.
• Particulate technology
P/M Processing Steps
Elemental or alloy
metal powders Additives (Graphite,
lubricants)
Blending
Compaction
Sintering
Optional Finishing operations
Finished product
Production of Metal Powders
ATOMIZATION
• Produces a liquid-metal stream by injecting molten metal through a small orifice
• The stream is broken up by jets of inert gas or air , Water
Atomization
Centrifugal Atomization
• The process in which the molten-metal drops onto a rapidly rotating disk or cup
• The centrifugal forces break up the molten-metal stream to generate particles
Centrifugal Atomization
Mechanical Alloying
• Also known as pulverization
• Involves roll crushing, milling in a ball mill, or grinding of brittle or less ductile metals into small particles
• Brittle materials have angular shapes
• Ductile metals are flaky and not particularly suitable for P/M
Compaction
• Methods of Compaction : Application of high pressure to the powders to form them
into the required shape – Green compact
•Mechanical Pressing
•Hot Isostatic pressing
•Cold Isostatic pressing
Compaction pressures : 100Mpa to 1000 Mpa
Isostatic pressing : 1500 -30,000 psi
Compaction : Die/Punch Tooling
Compaction cycle
Pressing in PM: (1) filling die cavity with powder by automatic feeder; (2) initial and (3) final positions of upper and lower punches during pressing, (4) part ejection.
Ho
t Is
ost
atic
Pre
ssin
g
Cold Isostatic Pressing
Sintering • Compressed metal powder is heated in a controlled
atmosphere furnace.
• to a temperature below its melting point which allows the bonding of materials to impart strength and hardness
Stages of product in P/M
Applications of P/M
• Abrasives: metal polishing wheels, grinding media
• Agriculture: lawn & garden equipments.
• Aerospace: jet engines, heat shields, rocket nozzles
• Ceramics: high temperature components, thermal shields, fuel cells
• Electronic: capacitors, resistors, contacts
• Hardware: locks, wrenches, cutting tools
• Manufacturing: dies, tools, bearings