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POWDER METALLURGY

POWDER METALLURGY

Manufacturing Process

Manufacturing Process

Lecture

Lecture

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Introduction

Introduction

Powder metallurgy, or P/M (pronounced

Powder metallurgy, or P/M (pronounced

PM), is a

PM), is a

process

process

for forming metal parts

for forming metal parts

by heating compacted metal

by heating compacted metal

powders

powders

to

to

just below their melting points.

just below their melting points.

Powder metallurgy is the study of the

Powder metallurgy is the study of the

processing of metal powders, including

processing of metal powders, including

the fabrication, characterisation, and

the fabrication, characterisation, and

conversion of metal powders into useful

conversion of metal powders into useful

engineering components.

engineering components.

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What do we learn?

What do we learn?

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Introduction to Powder

Introduction to Powder

Metallurgy

Metallurgy

Attraction of P/M : the

Attraction of P/M : the

ability

to

fabricate

ability

to

fabricate

high quality, complex

high quality, complex

parts

to

close

parts

to

close

tolerances

in

an

tolerances

in

an

economical manner.

economical manner.

Automated operation :

Automated operation :

low relative energy

low relative energy

consumption,

high

consumption,

high

material

utilisation,

material

utilisation,

and low capital costs.

and low capital costs.

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POWDER METALLURGY PROCESS

POWDER METALLURGY PROCESS

TOPICS
COVERED IN
THIS LECTURE

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Advantages of the P/M

Advantages of the P/M

Process

Process

Eliminates or minimises

Eliminates or minimises

machining.

machining.

Eliminates or minimises

Eliminates or minimises

scrap loses.

scrap loses.

Maintains

close

Maintains

close

dimensional tolerances.

dimensional tolerances.

Permits a wide variety of

Permits a wide variety of

alloy systems.

alloy systems.

Produces

good

surface

Produces

good

surface

finishes.

finishes.

Provides materials which

Provides materials which

may be heat-treated for

may be heat-treated for

increased

strength

or

increased

strength

or

increased wear resistance.

increased wear resistance.

Provides

controlled

Provides

controlled

porosity for self-lubrication

porosity for self-lubrication

or filtration.

or filtration.

Facilitates manufacture of

Facilitates manufacture of

complex or unique shapes

complex or unique shapes

which would be impractical

which would be impractical

or impossible with other

or impossible with other

metalworking processes.

metalworking processes.

Suited to moderate-to high

Suited to moderate-to high

volume

component

volume

component

production requirements.

production requirements.

Offers

long-term

Offers

long-term

performance reliability in

performance reliability in

critical applications.

critical applications.

Cost effective.

Cost effective.

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Applications for Metal

Applications for Metal

Powders

Powders

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POWDER CHARACTERISTICS

POWDER CHARACTERISTICS

P/M deals with particles

P/M deals with particles

that are larger than

that are larger than

smoke (0.01 to 1

smoke (0.01 to 1





m),

m),

but smaller than sand

but smaller than sand

(0.1 to 3 mm). Many

(0.1 to 3 mm). Many

metal

powders

are

metal

powders

are

similar in size to the

similar in size to the

diameter of a human

diameter of a human

hair (25-200

hair (25-200





m).

m).

What is a particle ?

What is a particle ?

Collecting

a

Collecting

a

representative sample of

representative sample of

powder for analysis can

powder for analysis can

be difficult. Sampling

be difficult. Sampling

errors can be avoided

errors can be avoided

using some simple rules.

using some simple rules.

Particle size and

Particle size and

distribution.

distribution.

Particle shape and its

Particle shape and its

variation with particle

variation with particle

size.

size.

Surface area

Surface area

Interparticle friction

Interparticle friction

Flow and packing

Flow and packing

The internal particle

The internal particle

structure

structure

Composition,

Composition,

homogeneity, and

homogeneity, and

contamination.

contamination.

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Particle Size

Particle Size

Particle size is a

Particle size is a

determination of the

determination of the

dimensions

of

a

dimensions

of

a

particle.

particle.

Most particle size

Most particle size

analysers use one

analysers use one

geometric

geometric

parameter and make

parameter and make

the assumption of a

the assumption of a

spherical

particle

spherical

particle

shape.

shape.

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Particle Size Distribution

Particle Size Distribution

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Particle Shape

Particle Shape

Particle shape influences

Particle shape influences

packing,

flow,

and

packing,

flow,

and

compressibility,

compressibility,

provides information on

provides information on

the powder fabrication

the powder fabrication

route, and helps explain

route, and helps explain

many

processing

many

processing

characteristics.

characteristics.

Particle shape varies with

Particle shape varies with

size and manufacturing

size and manufacturing

technique.*

technique.*

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Variations in Shape

Variations in Shape

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*Water Atomisation Process

*Water Atomisation Process

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Powder Structure

Powder Structure

A

magnified

cross

A

magnified

cross

section

through

a

section

through

a

powder

reveals

powder

reveals

artifacts that indicate

artifacts that indicate

Fabrication conditions

Fabrication conditions

Possible processing

Possible processing

problems

problems

Internal pores,

Internal pores,

segregation,

segregation,

inclusions, and oxides.

inclusions, and oxides.

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Powder Chemistries

Powder Chemistries

There are 3 groups of powder:

There are 3 groups of powder:

1.

1.

The elemental powders are

The elemental powders are

relatively high purity materials

relatively high purity materials

where chemical analysis focuses

where chemical analysis focuses

on the impurity concentration.

on the impurity concentration.

2.

2.

Premixed powders are

Premixed powders are

combinations of two or more

combinations of two or more

distinct powders that will

distinct powders that will

diffusionally alloy in sintering

diffusionally alloy in sintering

(concerns: impurity levels and

(concerns: impurity levels and

proper compounding of the

proper compounding of the

mixture).

mixture).

3.

3.

The prealloyed powders

The prealloyed powders

constitute micro-castings with

constitute micro-castings with

multiple elements in a

multiple elements in a

predetermined ratio (concerns:

predetermined ratio (concerns:

alloy composition and impurity

alloy composition and impurity

concentrations).

concentrations).

Surface Conditions:

Surface Conditions:

-

Oxides

Oxides

-

Adsorbed organic films

Adsorbed organic films

-

The presence of

The presence of

surface coatings like

surface coatings like

silica to determine

silica to determine

appropriate cleaning

appropriate cleaning

treatments

treatments

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Powder Adjustment to Improve Packing and

Powder Adjustment to Improve Packing and

Flow

Flow

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Packing Structures

Packing Structures

The packing density

The packing density

dictates the die fill,

dictates the die fill,

binder content, and

binder content, and

shrinkage in sintering.

shrinkage in sintering.

The greater the surface

The greater the surface

roughness or the more

roughness or the more

irregular the particle

irregular the particle

shape, the lower the

shape, the lower the

packing density.

packing density.

For common P/M

For common P/M

powders the packing

powders the packing

density ranges from

density ranges from

30-65% of theoretical.

30-65% of theoretical.

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Mixing and Blending

Mixing and Blending

Mixing and blending are

Mixing and blending are

necessary :

necessary :

to prepare unique

to prepare unique

particle size

particle size

distribution.

distribution.

Combine powders to

Combine powders to

generate new alloys

generate new alloys

during sintering.

during sintering.

Add lubricants for

Add lubricants for

compaction

compaction

To prepare a powder-

To prepare a powder-

binder mixture for

binder mixture for

shaping.

shaping.

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Shaping and Compaction

Shaping and Compaction

Injection Molding

Injection Molding

Slurry Techniques :

Slurry Techniques :

Slip casting and tape

Slip casting and tape

casting

casting

Freezing technique

Freezing technique

Extrusion

Extrusion

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Injection Molding

Slurry

Techniques

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COMPACTION

COMPACTION

To achieve greater

To achieve greater

densities requires

densities requires

an external

an external

pressure.

pressure.

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Stages of Compaction

Stages of Compaction

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Conventional Compaction

Conventional Compaction

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Density Lines after Compacted

Density Lines after Compacted

Powder

Powder

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SINTERING

SINTERING

Sintering is the

Sintering is the

bonding together of

bonding together of

particles at high

particles at high

temperatures.

temperatures.

T < Tm by solid-state

T < Tm by solid-state

atomic transport

atomic transport

(solid-state sintering)

(solid-state sintering)

Involves formation of

Involves formation of

a liquid phase (liquid-

a liquid phase (liquid-

state sintering)

state sintering)

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Sintering Theory

Sintering Theory

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Pore Structures in Sintering

Pore Structures in Sintering

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Liquid Phase Sintering

Liquid Phase Sintering

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Practical Sintering

Practical Sintering

Operations

Operations

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SECONDARY OPERATIONS

SECONDARY OPERATIONS