Materials engineering

Powder metallurgy

Outline

Process of powder metallurgy

Production of metal powders

Compaction

Sintering

PM products

Introduction

During powder metallurgy processes metal powders are

- compacted into desired shapes and

- sintered (heated without melting the metal)

to form a solid part.

net-shape forming

Process of powder metallurgy

http://www.youtube.com/watch?v=O7U4HWjYcqo

Powder producing process

Atomization of molten metal

Mechanical comminution

Reduction of metal-oxide Electrolytic Deposition Carbonyl process

Powder producing process

Atomization: injecting molten metal through a small orifice;

the stream is broken up by jets of inert gas, air or water

For low melting point materials: Sn, b, Zn, Al, Cu etc

Drop size: 200-400 m

Powder producing process

Mechanical comminution

For brittle alloys and carbides

Particle size: 20-400 m

Roll crushing Ball milling Hammer milling

Powder producing process

Reduction of metal oxide: W, TiC, Ta

WO3+3H2 W + 3H2O W + C WC ~1500C in vacuum

particle size: 0.5 ~10 m

TiO2 + 2C TiC + CO2

Co3O4 + 4H2 3Co + 4H2O

particle size: ~0.5 m

very fine metallic powder with spherical shapes

Powder producing process

Carbonyl process:

Me + n(CO) Me(CO)n

Me

Unstable

carbonyl compound

Decomposition

Fe, Ni and Co

Expensive

Extra clean and fine sized (~0.1m) Fe can be produced

Powder producing process

Electro deposition:

Electrolytic deposition utilizes either aqueous solutions

or fused salts. One of the purest method.

Blending Metal Powders

Mixing of metal powders according to the desired chemical

composition.

Uniformity of mechanical properties throughout the part.

Lubricants can be mixed with the powders to improve their flow

characteristics.

Other additives, such as binders

Compaction of Metal Powders

Brittle

High porosity

Compaction of Metal Powders

Cold Isostatic Pressing

uniform grain structure and density

almost 100% density

Hot Isostatic Pressing

Sintering

Initial unsiteredpowder particles

Sintered powder particles

A process whereby green parts are heated in a controlled

atmosphere furnace to a temperature below the melting point, but

sufficiently high to allow bonding by fusion of the powder particles

Depending on temperature, time, and the processing history, different

structures and porosities can be obtained which affect the properties.

PM products

Volume porosity > 30 % filters

18-30% bearings (oil soaks up into the pores)

7-18% textile machine parts, oil pump gears

PM products: Hard Metals

High hardness at elevated temperatures (e.g. HRc > 55 at 900C) High wear resistance

ISO HV B.S. WC TiC+TaC Co

P 0.1

P 50

1300

1800

700 MPa

2100 MPa

30 %

68 %

64 %

15 %

6 %

17 %

M 10

M 40

1750

1300

1350 MPa

2100 MPaRem. ~10 %

6 %

15 %

K 0.1

K 50

1800

1300

1200 MPa

2100 MPaRem. 1-4 %

4 %

12 %

G 0.1

G 40

1600

950

1500 MPa

2800 MPa

92 %

69 %1-2 %

6 %

30 %

Fo

r c

utt

ing

Fo

r c

old

fo

rmin

g

PM products: ASP High speed steels

Atomized powder loaded and vacuum sealed into steel

container

Compacted at room temperature

Heat to 1150C and compacted by hot rolling or forging

(~ 100 MPa pressure)

Homogeneous carbide distribution

Bending strength is doubled

High hot hardness

PM products

Cutting tools

PM products

Filters, catalyzers

PM products

Bearings

PM products

Machine parts