powder metallurgy

1. Powder Metallurgy
Essentially, Powder Metallurgy (PM) is an art &
science of producing metal or metallic powders, and
using them to make finished or semi-finished products.
Particulate technology is probably the oldest forming
technique known to man.
There are archeological evidences to prove that the
ancient man knew something about it.

2. Powder Metallurgy Process
 Powder production
 Blending or mixing
 Powder compaction
 Sintering
 Finishing Operations

3. Powder Metallurgy Process

4. Methods of powder production
Mechanical methods:-
 Milling
Machining
Shotting
Graining
Physical methods:-
 Electrolytic deposition
Atomization
Water Atomization
Gas Atomization
Vacuum Atomization
Centrifugal Atomization
Rotating disk Atomization
Ultrasonic Atomisation

5. Jaw crusher Gyratory crusher Roll crusher
Ball Mill Vibratory Ball Mill Attritor
Rod Mill Hammer Mill
Planetary
Mill

6. Electrolytic deposition:-
This method is mainly used for producing copper, iron
powders.
This method is also used for producing zinc, tin, nickel,
cadmium, antimony, silver, lead, beryllium
powders.
Reaction:
at anode: Cu -> Cu+ + e- at cathode: Cu+ + e- ->Cu

7. Atomization
•This uses high pressure fluid jets to break up a
molten metal stream into very fine droplets,
which then solidify into fine particles.

8. 1. Water atomization: High pressure water jets are used to
bring about the disintegration of molten metal stream.
Types of atomization:-
2.Gas atomization: Here instead of water, high velocity argon,
nitrogen and helium gas jets are used. The molten metal is
disintegrated and collected as atomized powder in a water bath
3.Vacuum atomization: In this method, when a molten metal
supersaturated with a gas under pressure is suddenly exposed into
vacuum, the gas coming from metal solution expands, causing
atomization of the metal stream.

9. Water atomization

11. Powder treatment & Handling
Cleaning of powder
Grinding
Powder classification and screening
Blending and mixing
uniform mixing random mixed un-mixed.

12. Conventional powder
metallurgy
production
sequence:
blending
compacting
Sintering

13. Blending
To make a homogeneous mass with uniform
distribution of particle size and composition.
Powders made by different processes have
different sizes and shapes
Mixing powders of different
metals/materials
Combining is generally carried out in
Air or inert gases to avoid oxidation
Liquids for better mixing, elimination of
dusts and reduced explosion hazards

14. Bowl Geometries for Blending Powders
Some common equipment geometries used
for blending powders
(a) Cylindrical, (b) rotating cube, (c) double
cone, (d) twin shell
A mixer suitable for blending metal powders.

15. Compaction
Application of high pressure to the powder to bring them
into the required shape.
• Press powder into the desired shape and size in dies using a
hydraulic or mechanical press
• Pressed powder is known as “green compact”
• Stages of metal powder compaction:

16. Compacting
Compacting is usually performed at room temperature. Pressures
range from 10 tons per square inch (tons/in2) (138 MPa) to 60
tons/in2 (827 MPa), or more.

17. Figure: (Left) Typical press for the compacting of metal powders. A
removable die set (right) allows the machine to be producing parts with
one die set while another is being fitted to produce a second product.

18. Sintering
Heat treatment to bond the metallic particles, thereby increasing
strength and hardness.
Usually carried out at between 70% and 90% of the metal's melting
point (absolute scale)
– Generally agreed among researchers that the
primary driving force for sintering is reduction of
surface energy
– Part shrinkage occurs during sintering due to pore
size reduction
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19.  Parts are heated to ~80% of melting temperature.
 Transforms compacted mechanical bonds to much stronger metal
bonds.
 Many parts are done at this stage. Some will require additional
processing.
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Sintering

20. Figure: Sintering on a microscopic scale: (1) particle bonding is
initiated at contact points; (2) contact points grow into "necks"; (3) the
pores between particles are reduced in size; and (4) grain boundaries
develop between particles in place of the necked regions.
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Sintering Sequence
 Parts are heated to 0.7~0.9 Tm.
 Transforms compacted mechanical bonds to much stronger
metallic bonds.

21. Third stage:
Sintered product is cooled in a controlled atmosphere.
–Prevents oxidation and thermal shock
Gases commonly used for sintering:
H2, N2, inert gases or vacuum
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Sintering

22. Advantages of P/M
 Virtually unlimited choice of alloys, composites, and
associated properties
 Refractory materials are popular by this process
 Can be very economical at large run sizes (100,000
parts)
 Long term reliability through close control of
dimensions and physical properties
 Wide latitude of shape and design
 Very good material utilization
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23. Limitations and Disadvantages
 High tooling and equipment costs.
 Metallic powders are expensive.
 Problems in storing and handling metal powders.
Degradation over time, fire hazards with certain
metals
 Limitations on part geometry because metal powders do not
readily flow laterally in the die during pressing.
 Variations in density throughout part may be a problem,
especially for complex geometries.
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24. PM Parts
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25. Connecting Rods:
Forged on left; P/M on
right
Powdered Metal Transmission Gear
 Warm compaction method with 1650-ton
press
 Teeth are molded net shape: No machining
 UTS = 155,000 psi
 30% cost savings over the original forged part
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26. Modern application of powder metallurgy
Used in both conventional aerospace application and
space vehicle system
Ex-
•Sintered bronze bearing (in explorer 3)
•Sinter magnets(navigational satellites)
•Beryllium(used for vehicle skins)

27. References:-
•Modern development in powder metallurgy by C G Goetzel.
•Paper submitted by R L ORBAN on new research directions in
powder metallurgy.
•Manufacturing technology (Vol-1) by P N Rao.

28. Thank You