Powder metallurgy is defined as producing metal or non-metal powders and using them to manufacture components. It involves basic steps of powder production, compaction, and sintering. Powder production methods include mechanical, physical, chemical, and electrochemical processes. Compaction forms a "green compact" by pressing powder in a die. Sintering heats the compact below melting to bond particles through solid-state diffusion. Applications include automotive, aerospace, defense, and industrial parts that benefit from net shape manufacturing or require properties unsuitable for other processes.

1. POWDER METALLURGY
BY
DR.RAHUL KHANDAGALE

2. History of Applications
• 3000 B.C. Egyptians made tools with
powder metallurgy
• 1900’s tungsten filament for light bulb
• 1930’s carbide tool materials
• 1960’s automobile parts
• 1980’s aircraft engine turbine parts

3. Powder Metallurgy (P/M)
• Competitive with processes such as
casting, forging, and machining.
• Used when
•melting point is too high (W,
Mo).
•reaction occurs at melting (Zr).
•too hard to machine.
•very large quantity.
• Near 70% of the P/M part
production is for automotive
applications.
• Good dimensional accuracy.
• Controllable porosity.
• Size range from tiny balls for ball-
point pens to parts weighing 100kg

4. Basic Steps In Powder
Metallurgy
• Powder Production
• Blending or Mixing
• Powder Consolidation
• Sintering
• Finishing

5. The P/M Process
• 3 Basic steps:
– Mixing
– Forming
– Sintering
• Optional
Manufacturing
steps are
sometimes
needed.

6. Making Powder-Metallurgy Parts

8. • Powder Metallurgy is defined as the
technique of producing metal & non metal
powders and utilizing them for
manufacturing components.
• Application:
Automotive- wipers, doors, clutches, brakes
Defence- rockets, missiles, bullets,cartridge
cases etc.
Refractory material.
Aerospace application such as satellite,
space vehicles.
Atomic applications such as reactors,
generators.

9. Steps in Powder Metallurgy
1) Powder production:
Methods:
a) Mechanical
b) Physical
c) Chemical
d) Electro-chemical

10. a) Machining:
• Use of machine tools to produce powders in the
form of chips.
• Relatively coarse powders of irregular shapes.
• Applications : Magnesium powders, beryllium
,silver solders, dental alloys, Cr powders for tracer
bullets in defence applications of fireworks.
b) Crushing:
The method use hammers, jaw crushers, gyratory
crushers etc.
Brittle materials - crushing irregular powders.
Ductile materials - elongated before fracturing
flaky in shape
Use: for brittle material like Ti,Zr,V

11. • Most widely used method.
• Rotating ball- mill machine is used.
• Tumbling performed as dry or wet In case
of wet water, alcohol or acetone is used.
• Application: Used for production of
carbide-metal and cermets.
c) Milling:
d) Shotting:
•Material is in hot boiling sate an poured on
vibrating screen.
•Liquid droplets are solidified in atmosphere.
Air or neutral gas as nitrogen.
•Application: Non ferrous metals.

12. Milling

13. Mechanical
Comminution/pulverization
(a) roll crushing, (b) ball mill, and (c) hammer milling.

14. • Graining method is similar to shotting
except cooling medium is water.
• Coarse powder in spherical form.
• Application: Pulverizing powders of metals
such as Zn, Bi, Tin etc.
e) Graining:
f) Atomization:
• Mechanical disintegration of molten metal by
high pressure of air or gas.
• Particles solidified in controlled atmosphere.
• Powder is spherical.
• Application: pure metal of Fe, Cu, Al

15. 1. Powder Production
(a) Water or gas atomization; (b) Centrifugal atomization; (c) Rotating electrode
• Many methods: extraction from
compounds, deposition, atomization,
fiber production, mechanical powder
production, etc.
• Atomization is the dominant process

16. Methods of metal-powder
production by atomization
• (a) melt atomization
• (b) atomization with a rotating

17. GAS ATOMIZATION

19. a) Condensation:
• Condensing metal vapors to obtain metal
powders.
• For volatile metals transforms to vapors.
• Carried out in controlled atmp. to avoid
formation of metal oxides.
• Application: Mfg. of powders for Zn, Mg, Cd
2) Physical Processes

20. b) Thermal decomposition
(Gaseous Pyrolysis)
• Based on decomposing the carbonyl vapors of
metal at controlled temp. and pressure and
breaking the metal into powder.
• Decomposed powder is of high purity and
spherical in shape.
Application
• For metal carbonyls such as Fe, Ni, Mo, Co.
• Using carbon-monoxide then decomposition of
carbonyl vapors to metal powder.
• Carbonyls are volatile and vapors decompose
at temp. 150 – 4000C and pressure at 1 atm.

21. 3) Chemical processes
a) Reduction:
Breaking the oxide, oxalates, formates or
halides of metals into metal powder by
using a suitable reducing agent.
Application: To obtain powders of Fe, Cu,
Ni, W, Mo, Co.
The reducing agent may be solid or gas
such as carbon, hydrogen, ammonia,
carbon monoxide

22. b) Intergranular corrosion:
Grain boundaries corrode faster than the grains.
Due to corrosion Grains separate out in the form
of poly crystalline metal.
Applications
• Stainless Steel – Fe, Cr, Ni
(Cr combines with C form complex carbide-then
carbide is corroded by boiling the steel in
aqueous solution of 11% CuSo4 and 10 %
H2SO4)
[Now atomization is used to obtain Fe powder]

23. • C) Precipitation
Less noble metal displaces a more noble metal in
an aqueous solution containing ions of more
noble metal.
The more noble metal thus separates out in the
form of precipitates.
Application
Powder production of Ag, Sn, Cu
Ag is displaced from an aqueous solution of silver
nitrate by Cu or Fe
Sn is displaced from an aqueous solution of
stannous chloride by Zn.
Cu is displaced from aqueous solution of CuSo4 by
Fe

24. 4) Electro-chemical Processes
• Based on electro deposition or electroplating
Metal powders are obtained by electro-deposition from
metal aqueous solutions or fused salts.
• In electro-plating a continuous & adherent coating
of metal is formed on the cathode component
while in electro deposition ,a coarse and non-
adherent layer is formed on the cathode
The powder size and type can be controlled by
High current, Low metal ion concentration, Low
temp. proper circulation of electrolyte
Application
Powder of Cu, Be, Fe, Zn, Sn, Ni

25. Electrochemical action: Solution of metal salt 
Current 
Metal deposits on cathode

26. Electrolytic

27. Step 2:Powder Conditioning
• Powder obtained by earlier method may
not be used in compacting
Heat treatment
Sieving
Blending or mixing
Powder Conditioning

28. Heat treatment
• HT is carried out to
- Eliminate work hardening effects
- Reduce oxide content
- Reduce impurities
- Alter apparent density
HT-Annealing (reducing atmosphere)
High temp annealing
- pressure apparent density
Low temp annealing
-pressure apparent density

29. • Powders should be evaluated for their
suitability for further processing
• Flow rate measures the ease with which
powder can be fed and distributed into a die
• Apparent density is the measure of a powder’s
ability to fill available space without external
pressure
• Compressibility is the effectiveness of applied
pressure
• Green strength is used to describe the
strength of the pressed powder after
compacting
Powder Testing and Evaluation

30. Sieving
• Non uniform size of powder leads to alteration
of properties of final component
• Powder is passing over a set of std. sieves
and only the desired powder size is retained
for further processing
Blending or Mixing
• To obtain a homogenous mix. of powders to
improve the compacting and sintering
properties.
• Blenders-lubricants, gas or vapours
• Binders - increase green strength

31. Some common equipment geometries used for
blending powders
(a) Cylindrical, (b) rotating cube, (c) double cone,
(d) twin shell

32. Step 3 Powder Compacting or Pressing
• Process of pressing and shaping to
powders in a die and punch
• Methods:
- Pressure less compacting
- Cold pressure compacting
- Hot pressure compacting

33. Powder Pressing
Punch
Punch
Die Part
Dual action press

34. Compacting
• Loose powder is compacted and densified into a
shape, known as green compact
• Most compacting is done with mechanical presses
and rigid tools
– Hydraulic and pneumatic presses are also used

35. Figure 18-3 (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.

37. Compaction
(a) Compaction of
metal powder to
form a bushing.
The pressed
powder part is
called green
compact.
(b) Typical tool and
die set for
compacting a
spur gear.

38. • Increased compaction pressure
– Provides better packing of particles and
leads to ↓ porosity
– ↑ localized deformation allowing new
contacts to be formed between particles

39. • At higher pressures, the green density approaches
density of the bulk metal
• Pressed density greater than 90% of the bulk density
is difficult to obtain
• Compaction pressure used depends on desired
density

40. • Smaller particles provide greater strength mainly
due to reduction in porosity
• Size distribution of particles is very important. For
same size particles minimum porosity of 24% will
always be there
– Box filled with tennis balls will always have open space
between balls
– Introduction of finer particles will fill voids and result in↑
density

41. Density Variation
• Density variation in compacting metal powders in different dies:
• (a) and (c) single-action press
• (b) and (d) double-action press.
• Note in (d) the greater uniformity of density in pressing with two
punches with separate movements as compared with (c).
• Generally, uniformity of density is preferred, although there are
situations in which density variation, and hence variation of
properties, within a apart may be desirable.

42. Complex Compacting
• If an extremely complex shape is desired,
the powder may be encapsulated in a
flexible mold, which is then immersed in a
pressurized gas or liquid
– Process is known as isostatic compaction
• In warm compaction, the powder is heated
prior to pressing
• The amount of lubricant can be increased
in the powder to reduce friction
• Because particles tend to be abrasive, tool
wear is a concern in powder forming

43. Cold Isostatic Pressing(CIP)
• Schematic illustration of
cold isostatic pressing
as applied to formation
of a tube. The powder is
enclosed in a flexible
container around a solid
core rod. Pressure is
applied isostatically to
the assembly inside a
high-pressure chamber.

44. Hot-Isostatic Pressing
• Hot-isostatic pressing (HIP) combines
powder compaction and sintering into a
single operation
– Gas-pressure squeezing at high temperatures
• Heated powders may need to be protected
from harmful environments
• Products emerge at full density with
unifrom, isotropic properties
• Near-net shapes are possible

45. Hot Isostatic Pressing(HIP)

46. Other compacting and shaping
operations
• Rolling
• Extrusion
• Spray Deposition

47. Powder Rolling

48. Powder Extrusion

49. Spray Casting
Spray casting (Osprey process) in which
molten metal is sprayed over a rotating
mandrel to produce seamless tubing and
pipe..

50. Densitry
of
compact
Compacting pressure
Density depends on pressure applied
Generally between 1 to 150 kg/mm2
Different Mechanism to apply pressure:
Explosive
HER
Powder rolling
Extrusion
vibratory
Isostatic

51. 3. Powder Consolidation
• Cold compaction with 100 – 900
MPa to produce a “Green body”.
– Die pressing
– Cold isostatic pressing
– Rolling
– Gravity
• Injection Molding small, complex
parts.

52. Characterization of Powders
• Size of powders 0.1 um – 1 mm
• Sieve size quoted as mesh
number
• Particle D = 15/mesh number (mm)
• 325 mesh 45 um

53. Sintering

54. • In the sintering operation, the pressed-
powder compacts are heated in a controlled
atmosphere to right below the melting point
• Three stages of sintering
–Burn-off (purge)- combusts any air and
removes lubricants or binders that would
interfere with good bonding
–High-temperature- desired solid-state
diffusion and bonding occurs
–Cooling period- lowers the temperature of
the products in a controlled atmosphere
• All three stages must be conducted in
oxygen-free conditions

55. Carried out in three stages:
• First stage: Temperature is slowly
increased so that all volatile materials in the
green compact that would interfere with
good bonding is removed
– Rapid heating in this stage may entrap
gases and produce high internal
pressure which may fracture the compact

56. • Promotes solid-state
bonding by diffusion.
• Diffusion is time-
temperature sensitive.
Needs sufficient time
Second stage: High temperature stage

57. •Promotes vapour-phase
transport
•Because material
heated very close to
MP, metal atoms will
be released in the
vapour phase from the
particles
•Vapour phase
resolidifies at the
interface

59. • 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

61. • Liquid Phase Sintering
• During sintering a liquid phase, from
the lower MP component, may exist
• Alloying may take place at the particle-
particle interface
• Molten component may surround the
particle that has not melted
• High compact density can be quickly
attained
• Important variables:
– Nature of alloy, molten component/particle
wetting, capillary action of the liquid

62. 4. Sintering
• Parts are heated to 0.7~0.9
Tm.
• Transforms compacted
mechanical bonds to much
stronger metallic bonds.
• Shrinkage always occurs:
sintered
green
green
sintered
V
V
shrinkage
Vol




_ 3
/
1
_ 








sintered
green
shrinkage
Linear



63. Sintering on Particles

64. Sintering

65. Powder Compaction and Sintering

66. Sintering
• The process whereby compressed metal
powder is heated in a controlled atmosphere
furnace to a temperature below its melting
point, but high enough to allow bonding of
the particles.
• Sintered density depends on its “green
density” and sintering conditions
(temperature, time and furnace atmosphere).
• Sintering temperatures are generally within 70
to 90% of the melting point of the metal or
alloy.
• Times range from 10 minutes for iron and
copper to 8 hours for tungsten and tantalum

67. • Sintering mechanisms are complex and
depend on the composition of metal
particles as well as processing
parameters. As temperature increases
two adjacent particles begin to form a
bond by diffusion (solid-state bonding).
• If two adjacent particles are of different
metals, alloying can take place at the
interface of two particles. One of the
particles may have a lower melting point
than the other. In that case, one particle
may melt and surround the particle that
has not melted (liquid-phase sintering).

72. Secondary Operations
• Most powder metallurgy products are
ready to use after the sintering process
• Some products may use secondary
operation to provide enhanced precision,
improved properties, or special
characteristics
• Distortion may occur during nonuniform
cool-down so the product may be
repressed, coined, or sized to improve
dimensional precision

73. Secondary Operations
• If massive metal deformation takes place in the
second pressing, the operation is known as P/M
forging
– Increases density and adds precision
• Infiltration and impregnation- oil or other liquid
is forced into the porous network to offer
lubrication over an extended product lifetime
• Metal infiltration fills in pores with other alloying
elements that can improve properties
• P/M products can also be subjected to the
conventional finishing operations: heat
treatment, machining, and surface treatments

74. Design Aspects
(a) Length to thickness ratio limited to 2-4; (b) Steps limited to
avoid density variation; (c) Radii provided to extend die life,
sleeves greater than 1 mm, through hole greater than 5 mm; (d)
Feather-edged punches with flat face; (e) Internal cavity requires
a draft; (f) Sharp corner should be avoided; (g) Large wall
thickness difference should be avoided; (h) Wall thickness should
be larger than 1 mm.

75. Advantages and Disadvantages of P/M
• Virtually unlimited choice of alloys, composites, and
associated properties.
– Refractory materials are popular by this process.
• Controlled porosity for self lubrication or filtration
uses.
• Can be very economical at large run sizes (100,000
parts).
• Long term reliability through close control of
dimensions and physical properties.
• Very good material utilization.
• Limited part size and complexity
• High cost of powder material.
• High cost of tooling.
• Less strong parts than wrought ones.
• Less well known process.

76. Advantages and Disadvantages
of Powder Metallurgy
• Advantages
– Elimination or
reduction of
machining
– High production
rates
– Complex shapes
– Wide variations in
compositions
– Wide property
variations
– Scrap is eliminated
or reduced
• Disadvantages
– Inferior strength
properties
– High tooling costs
– High material cost
– Size and shape
limitations
– Dimensional
changes during
sintering
– Density variations
– Health and safety
hazards

77. Basic Processing Steps

78. Products and applications