powder 111

1. Powder Metallurgy
By Group 15 :
- 191119073 Aliya Rahmani
- 191119074 Aman Rai
- 191119075 Abhinav Shrivastava

3. Powder Metallurgy
By Group 15 :
- 191119073 Aliya Rahmani
- 191119074 Aman Rai
- 191119075 Abhinav Shrivastava

4. Powder Metallurgy
By Group 15 :
- 191119073 Aliya Rahmani
- 191119074 Aman Rai
- 191119075 Abhinav Shrivastava

5. Contents
1. Introduction of powder metallurgy, certain products made from PM
2. Procedure of Powder Metallurgy(Flowchart)
3. Powder Manufacturing
4. Advantages, Disadvantages and Application of Powder Metallurgy

6. Introduction To Powder Metallurgy
• It is a very special way of manufacturing parts exactly as per dimensions & with
special properties by using metal powders.
• As the name suggests, the parts are manufactured by mixing & binding powders of
different metals & non-metals and compacting them to a specified geometry or
shape.
• Basically it is a modified method of manufacturing different from conventional
Casting, Forging, etc. processes.
• Parts with special properties, Components of refractory & super-hard materials,
Parts having combinations of plastics, metals & other different combinations, etc.
can be made from this method.

7. Certain Products Made from Powder
Metallurgy
• Porous Self-Lubricating
Bearings
• Porous metal sheets
• Cemented Carbides
• Metallic Filters
• Electric Contacts
• Friction materials
• Motor brushes
• Ductile tungsten
• Magnetic materials
• Diamond Impregnated Tools
• Babbit bearings
• Metallic Coatings
• Metal & Glass Seals
• Gear pump rotors
• Composites of refractory
Materials
• Cam shaft sprocket wheel
• Parts with variation in
composition & materials
• Wire Drawing dies
• Stone Hammers

8. Procedure of Powder Metallurgy
Powder Production
• Atomisation,
• Electrolysis
• Reduction,
• Pulverization, etc.
Mixing/Blending
• Adding Lubricants,
• Alloy additives, etc.
Compacting
• Machine Pressing,
• Rolling,
• Extruding, etc.
Pre-Sintering Processes
• Heat treatment,
• Surface preparation, etc.
Sintering
• Heating the compact at certain
pressure
Post-sintering/ Secondary
Operations
• Infiltration
• Repressing
• Machining, etc.
Finished Powder Metallurgy Parts

9. Powder Manufacturing
1. Atomization
• As the name suggests, in this method the molten metal cools
down in very small atom like shape powder.
• Molten metal is poured in tundish using ladle & made to pass
through a small nozzle.
• A pressurized jet of water or gas (generally about 2-3 kg/cm²)
is applied to melt coming out of nozzle.
• To improve quality of powder, inert gases can be used.
• Because of jet, the melt gets cooled in shapes of very fine
spherical/pearl shaped powder and is collected at base of
chamber.
• The size of powder is dependent on Nozzle size, Rate of Metal
flow & Temp. and Pressure of jet.
• Suitable for metals having low melting points like Al(660˚C),
Sn(232˚C) & Zn(420˚C).

10. 2. Reduction
• It is a chemical process of gaining electrons by
atoms of a substance.
• For this purpose, Oxides of materials are reduced
using C (charcoal), CO & H.
• The powder is produced by crushing & screening
the product of reduction at below the melting point
of the material.
• WO + 𝐻2= W + 𝐻2O
• 𝐶𝑢2O + 𝐻2 = 2Cu + 𝐻2O
• 𝐹𝑒3𝑂4 + 4CO = 3Fe + 4𝐶𝑂2
• This process is cheap, easy & flexible and suitable
for metals whose oxides are easily available.
• Majority of metal powder is produced by this
method in industries.

11. 3. Electrolysis/Electrolytic Deposition
• This is a Electro-chemical process used to obtain extremely pure
powder of metals like Cu, Fe, Ta, Ag, Zn & Sn.
• Powder produced has good oxidation resistance.
• The setup is similar to Electroplating, that is metal whose
powder is to be made is selected as Anode & Al (general
preference) plate is selected as Cathode.
• These electrodes are dipped in a suitable Electrolyte as per
Anode material (i.e. CuS𝑶𝟒 for Cu).
• When high ampere current is passed through them, a layer of
Anode metal is deposited over Cathode.
• After sometime, Cathode is removed from tank, rinsed & dried.
• Then the material deposited is scraped off from it & grinded to
produce powder of required size.

12. 4. Mechanical pulverisation (Milling)
• This method can produce fine powders of brittle
materials of particle size of minimum 0.001mm.
• The materials are disintegrated to desired size by
crushing, rolling & milling.
• Then this crushed metal is further ground in a ball mill in
which steel balls impinge upon the powder
simultaneously to grind it to required size.
• For fine grinding of powder, heavy crushing machines,
crushing rolls, etc can be used.

13. 5. Condensation
• This is a fast & cheap method used for metals having
very low boiling points like Zn, Cd, Mg, Pb, Sn, etc.
• In this method, a metal rod is kept against a high
temperature flame.
• Eventually, the metal starts boiling.
• There is a cold surface(which doesn’t adhere with
metal drops) above the rod on which the vapour of
metal condenses directly in the form of fine powder
particles.
• Then this powder is removed from the surface.
• This method is not suitable for mass production of
powders.

14. 6. Hydride & Carbonyl Processes
• Metals like Ta, Nb & Zr, etc. when subjected to Hydrogen, forms stable hydrides at
room temperature.
• Again when these hydrides are heated at about 350˚C, they dissociate into Hydrogen
& powder of pure metal.
• Carbonyl method is useful for Ni & Fe.
• In this method, the metal is made to combine with CO and form Volatie Carbonyls.
• Fe(𝑪𝑶𝟓) is a colourless volatile liquid which boils at 107˚C & Ni(𝑪𝑶𝟒) boils at 43˚C.
• These are obtained by passing CO gas over the metal at suitable temperature (200-
270˚C) & pressure (70 - 210 bars)
• Ni + 4CO Ni(𝐶𝑂4)
• The carbonyls formed are boiled and made to decompose in a cooled chamber to
obtain spherical pure metal powder deposits.
• There is no wastage of either gas or metals.

15. Powder Metallurgy-2
By:-
Mayank G. Jain

16. Properties of Metal Powder
• Purity of powder material :- Important for determining base
properties & structure
• Chemical composition of powder material :- Needed for
considering the effect of various processes to be carried out in
future.
• Particle Size :- Influences mould strength, density of
compact, porosity, permeability, flow & mixing properties as
well as dimensional stability.
It is generally expressed in terms of diameter of particles.
• Particle size distribution :- Influences packing of powders &
behaviour during moulding and sintering.
It is determined using sieve analysis.

17. • Particle shape :- Impacts flow characteristics & packing
characteristics.
 Spherical powder has good properties.
• Flow rate :- It can be defined as the rate at which metal powder flow
& fill up the die cavity completely. It helps in determining production
rate.
 Spherical particles have high flow rate whereas dendritic particles
have lowest flow rate.
• Apparent density :- The weight of loosely heaped quantity of powder
requires to fill the die cavity completely is known as it’s apparent
density.
• Microstructure :- Microstructure of particle will affect the final
properties of Powder Metallurgy component.

18. Need for Mixing or Blending
• Why Mixing & Blending are required in Powder Metallurgy
components?
After the metal powders are produced by any of the production
method, they cannot be directly used for compacting (except by
reduction) into a shape because they don’t possess the required
physical or chemical characteristics.
So, powders are conditioned by certain specific techniques like
blending & mixing to obtain correct composition, form & properties.

19. Blending
• In this process, lubricants, volatizing agents or other compounds are added in powder.
• Blending gives following benefits:-
The wear of tools & dies used for compacting is reduced & pressure needed for
compacting is also reduced.
To produce alloys by adding different elements as per requirement.
To get uniform distribution of particles resulting in uniformity of properties of
components produced.
To obtain required porosity in certain parts.
To reduce compaction time due to internal lubrication instead of lubrication from tools
& dies.

20. Mixing
• Required to produce uniform distribution of powder, particularly when
different size of powders are used.
• Compact produced after proper mixing has uniform density.
• Mixing can be done either directly (dry powder form) or in special cases
as wet mixing (using water or solvent).
• Wet mixing reduces the amount of dust particles, prevents oxidation of
particle surfaces.
• Moreover, wet mixing considerably reduces chances of accident while
mixing powders of explosive materials.

21. Powder Metallurgy-3
By:-
Mayank G. Jain

22. Powder Compaction
• It is the operation of pressing the blended particles together to form the required shape of
part.
• Generally, the compaction is done in cold state resulting in cold welding of powder particles.
• The powder is compacted with an aim to consolidate the powder into the desired shape with
near net final dimensions by considering any dimensional changes that may occur due to
sintering.
• Compacting is so designed to provide required strength & porosity.
• There are two types of compacting techniques:-
1. Pressure compacting (Die pressing, Roll pressing, Extrusion method, Vibratory
compacting, High-Energy-Rate forming, etc.)
2. Pressure-less compacting (Slip casting, Continuous compaction, etc.)

23. Die Pressing
• This is the most commonly used pressure
compacting technique by using special
Mechanical or Hydraulic presses including Feed
hopper, Shaping dies, Upper punch & lower
punch.
• First, die cavity is filled with powder blend
through a feed hopper in a definite quantity.
• This blend is pressed using adequate pressure
between upper & lower punches by moving
them towards each other.
• Now the pressed compact called “Green
Compact” or “Briquette” is ejected by moving
the lower punch further up.

24. • Mechanical presses provide pressure range between 100kN-5MN for a variety of metals.
• They provide high speed production rates, flexibility in design, simplicity, economy of
operation & relatively low investment cost.
• Hydraulic presses can provide even higher pressure, but slower stroke speeds (less than
20 strokes/min). Therefore they are used for complicated parts requiring high pressure
only.
• The compaction pressure depends upon:-
Required density of final product
Size & Shape of the powder particles
Physical & Mechanical properties of metal

25. Roll Pressing
( Continuous Pressure compacting)
• This method is used to produce continuous
sections by passing metal powder blend between
two rollers set at adequate distance.
• Due to rolling action, a regulated stream of
powder is guided during which necessary pressure
is applied continuously.
• To alter the properties of compact, the roll gap can
be adjusted.
• They are used to manufacture simple shapes like
rod, sheet, tube & plates.
• Note:- The speed of rollers is much less as
compared to conventional rolling process.

26. Extrusion Technique
• This is also a pressure compacting technique in which
the metal powder is filled in a container having die
opening & ram on either same side or opposite sides.
• The sealed container is heated and then ram applies
pressure & forces the metal powder out from
opening.
• The extruded part is generally having the cross-
section of die opening and form of rod , wire or
plate.
• This method is also widely used fore plastic parts
manufacturing, similarly by using plastic powders.
• But for metals, it has a limited application due to
inefficient control.
Forward Extrusion
Backward Extrusion

27. High-energy-rate forming
• These are high pressure compacting techniques having four
types:- mechanical, pneumatic, explosive-discharge & spark-
discharge method.
• The last two methods are carried out in a closed die.
• In Explosive discharge method, a layer of powder blend having
suitable thickness is applied on a die having the shape of
component.
• There is a vacuum tube in die to allow escaping of air between
powder blend.
• This assembly is submerged in a suitable cooling solvent.
• Now an explosive is made to explode just above the powder.
• The shockwave of the explosion applies the required pressure
and produces a uniform thickness “green compact”.

28. Vibratory compaction
• This is also a pressure type compacting method but
requires less pressure as compared to others.
• The phenomenon responsible for compacting here is
vibratory oscillation which removes the air gaps
between particles.
• This action is quite similar to compacting the wheat
flour in a container by externally beating the
container to settle down the flour.
• Due to this, the powder is uniformly laid out thereby
reducing the pressure required for compacting.
• The vibrations are produced by reciprocating the
table by motors & after they are laid out, they are
compacted using punch & die.

29. Slip Casting
• This is a pressure-less compacting technique used
majorly for ceramic powders as compared to metals.
• In this method, a slip (slurry of powder & liquid solvent)
is used.
• The solvent is selected such that the powder remains
suspended and doesn’t settle down in liquid.
• Now this slip is poured in a porous mould having shape
of part to be produced.
• Due to porosity of mould, the liquid starts being absorbed
by mould at mould walls, leaving behind a powder layer
under liquid pressure.
• The most important factor is time, according to which the
thickness of part is determined.
• Then the remaining liquid slip is poured out & after
sometime the briquette is separated from the mould.

30. Continuous pressure-less compaction
• This method is used to obtain porous metal sheets for Ni-Cd batteries.
• Powder is applied directly on a flat metal screen in the form of a slurry similar to
the slip.
• The thickness is kept a little more than required during the process, so after pre-
sintering operations the actual dimensions are obtained.
• After sometime, the volatizing liquid component vaporize to leave behind
unusual composite powder coating on the screen.

31. Powder Metallurgy-4
By:-
Mayank G. Jain

32. Pre-Sintering Operations
• Sometimes, the briquette cannot be directly sintered. This is
because for sintering the part should be accurate to dimensions
& must have considerable strength.
• These properties are achieved using pre-sintering. Moreover, the
dimensional stability of the part also increases during sintering.
• For pre-sintering, the temperature & pressure utilized are of
much smaller margin than sintering.
• The blended volatizing agents & excess lubricants are also
removed during this process.
• Machining of sintered part can be avoided if pre-sintering is
carried out.
• Pre-sintering may be eliminated if no machining of final
product is required.

33. Sintering
• The briquette is sintered to provide possible final strength & hardness
required for finished part.
• Sintering consists of heating the briquette in a furnace (continuous/batch type
& oil/gas fired) to a temperature below the highest melting point from the
major constituents in an Inert (reducing) atmosphere.
• The reducing atmosphere is utilized to prevent formation of oxidized
coatings on metal particles.
• H is used as reducing agent for W & WC, dissociated 𝑵𝑯𝟒 is used for Fe-C
alloys, partially burnt coal gas is used as reducing agent for Brass & Bronze,
etc.
• Technically sintering is a process of bonding solid particles by thermal
diffusion.
• The bonding is divided in 3 stages:- a) neck formation at particle contact, b)
neck growth, c) pore rounding
• Sintering is classified in two groups:-
1. Solid phase sintering
2. Liquid phase sintering

34. Solid phase Sintering
• In this process, neither of the compacted
metal melts but rather the grain growth &
diffusion takes place at cold-welded locations
of powder.
• Because of diffusion & grain growth, bonding
of adjacent particles takes place.
• This results in a cellular structure of powder
grains.
• Pure tungsten is sintered in this manner.

35. Liquid Phase sintering
• In this process, one of the constituents whose
melting point is low melts & forms a continuous
phase of material surrounding other constituents.
• This continuous phase acts like a bond of element
supporting other constituents and is responsible
for holding particles together & providing
strength.
• Bronze and Cemented Carbide tips are sintered
by this process.

36. Hot isostatic pressing/hipping
• This is a modern industrial approach for performing
compacting & sintering simultaneously using inert gases.
• In this process, powder is filled in a closed pressure
chamber as in adjacent figure.
• An inert gas (usually Argon) is sent in this chamber at
suitable pressure for compacting the powder.
• The heaters are used for sintering the powder.
• Due to combined action of pressurized gas & heaters, the
powder gets compacted & sintered.
• However, the porosity obtained is very less in such parts.
Hence, this method is majorly used for cemented carbide
parts and has limited application for other parts.

37. Post-sintering Operations
• To obtain a specific & desired level of finish, tolerances or internal metal structure
in Briquette, these operations may be performed.
• As we have previously discussed, that not all properties required are readily
available in powder metallurgy parts, the need of such operations may arise.
• The majorly performed operations are as follows:-
1. Sizing (correcting dimensions) 5. Heat treatment
2. Coining ( repressing to reduce
voids
6. Joining
3. Machining 7. Infiltration
4. Plating/Coating 8. Impregnation

38. Infiltration
• Parts manufactured by powder metallurgy have theoretical density of about 77%.
• To achieve density close to 100%, infiltration process is carried out.
• A replica of other metal (say Cu or Brass having melting point lower than part
material) in calculated volume is kept above part produced by Powder Metallurgy
and kept in a furnace.
• The replica melts and enters the pores of part & fills the cavities to achieve
theoretical 100% density.
• Moreover, the strength & hardness are also improved for the part.

39. Impregnation
• In this process, the cavities in parts are filled by oil, grease, wax or any other lubricating
materials.
• This is specially done for antifriction components to make them self-lubricating as in case
of bearings.
• This is done by dipping the porous bearings made by powder metallurgy in a container
having lubricating oil at 93˚C.
• The pores get filled up in 20-30 minutes due to capillary action of oil in pores and is
retained in the parts.
• Sometimes, bearing materials having low melting point like tin & lead babbit are
impregnated in bearings to provide a spongy non-ferrous matrix which further improves
bearing properties of parts.
• Some parts are also impregnated by plastics to improve corrosion resistance, sealing,
machinability & pressure tightness properties.

40. Production of cemented carbide tools by Powder
Metallurgy
6 parts C
Tantalum
Oxide
Titanium
Oxide
Tungsten
oxide
94 parts W 6 parts C
94 parts Ti 20 parts C
80 parts Ta
Milling
Carburizing to
respective carbides
Cobalt + Cobalt
Oxide
Blending &
Granulating
Paraffin added
& dried
Compacting
Sintering
Diamond grinding of
sintered parts
Cemented
carbide tools

41. Specific parts made by
Powder Metallurgy
1. Cemented Carbide Tools
• They are tools having extremely hard
phase well distributed in a tough matrix.
• They retain hardness due to W, Ti & Ta
along with toughness due to soft matrix
material.
• They are suitable for high speed cuttings
as they have good hot hardness & can
absorbs shock loads.
• However, the whole tool cannot be made in
this method as it will be brittle.
• Hence, they made in the form of indexable
insert tips which can be mechanically
joined to a tool shank.
2. Self-lubricating Bearings
• They are impregnated by lubricants.
• At stationary condition, the lubricant is
retained in part and forms a thin film over
surface to provide initial lubrication.
• As the rotation starts & speed increases,
more heat is generated resulting in seeping
out of oil from pores and providing
necessary lubrication.
• Again as shaft stops, the oil is absorbed in
the pores of bearings by capillary action.
• Because of this property, they require
considerably less maintenance & repair as
compared to normal bearings.

42. Powder Metallurgy-5
By:-
Mayank G. Jain

43. Advantages of Powder Metallurgy
1. Reduction or elimination of Machining:- Parts produced by Powder Metallurgy are
made within very small dimensional tolerances, hence the need of machining is greatly
reduced.
This also reduces the wastage of material (less than 3%).
2. High Production rates:- Speeds as high as 60 stokes/min can be achieved while
compacting & hundreds of components can be sintered at the same time.
Even all the other processes are fast & consumes less time thereby increasing Production
rate.
3. Production of Complex Shaped Parts:- Various materials have limited flowability in
molten state which is not sufficient for casting complex & intricate shapes. However, the
powders may have better flowability & can be easily compacted in required complex shapes.

44. 4. Possibility of variation in Composition:- The material composition can be easily
controlled by powder shapes, sizes & additives.
Moreover, the pressure during compacting can be varied to achieve controlled porosity
& density.
5. Possibility of wide variation in properties:- By controlling Die pressure, Powder
properties, sintering temperature, etc. we can easily alter the properties throughout part as
per our requirements.
6. Production of parts not producible by other methods:- Self-lubricating bearings,
porous parts, parts with metals & non-metals, parts having layers of different materials.
7. Freedom from Equilibrium diagram limitations:- As per solubility, some metals
cannot be casted together to form alloys. But powders can easily be blended & sintered
together. Examples are combination of Cu-Pb, Sn-Plastic, Copper-Graphite, etc.

45. 8. The reproducibility of the shapes is excellent using this process.
9. The grain size can be controlled & parts without voids & blow holes can be
produced.
10. Parts using Refractory, super hard & non-metallic materials can be made.
11. Porous parts can only be produced by this method.
12. Use of diamond impregnated tools is possible due to Powder metallurgy.

46. Disadvantages of Powder Metallurgy
1. Inferior Mechanical Properties:- Due to residual Porosity, the tensile strength, yield
strength, toughness, etc. are reduced.
2. High Initial Cost:- The capital investment for dies & press tools, etc is very high.
Moreover, they also Require frequent maintenance & repair due to wear & tear due to
cold welding of powder on dies.
Thus, powder metallurgy is only viable for mass production(Qty. more than 10,000).
3. Costlier raw materials:- The production of powders of various metals & non-metals is
very costly adding to the total cost of product.
4. Limitations imposed by Materials:- Some powders lack the ability to flow freely
without pressure, this increases the pressure required for compacting.
Due to this sharp corners, long-thin sections & varying cross-sections become difficult
to produce using Powder Metallurgy.

47. 5. Limitations imposed by design:- Design of parts is restricted by press capacity, length of
stroke & work area on press.
Because of this parts with close tolerances, thin walls, holes at right angle to pressing,
reverse tapers, etc.
Manufacturing of very big parts is also restricted by press tool dimensions.
Moreover, provision for easy ejection from die is also required in parts.
6. Undesired Property Variation within parts:- Usually as compacting applies pressure
from top, the parts are more dense at top & less dense at bottom surface. Such a non-
homogeneity reduces the life of parts.
7. Hazards/Safety limitations:- Powders of radioactive, toxic & explosive materials require
utmost care in powder metallurgy along with a very high level of controlled atmosphere or
accident may occur.

48. Applications of Powder Metallurgy
1. Porous & Permeable parts:- Self-lubricating bearings, filters, porous plugs, pressure & flow
regulators, etc. are components requiring porosity which are manufactured by Powder metallurgy. Pores
as small as 0.0025mm can be obtained.
2. Production using Refractory metals & Composites:- Parts from metals like W, Mo, Ta & pt, etc.
cannot be made by melting & casting conventionally.
Many cutting tools have ceramic (oxides, nitrides, borides, etc.) as main constituent and W-C, Ti-Co-
C, etc as binders to form composite materials having both hardness & toughness.
3. Products made from difficult to machine materials:- Tungsten filament is a very small & super
hard part which cannot be machined conventionally. Hence, powder metallurgy is needed.
4. Complex & intricate parts:- Small gears, Cams, levers, sprockets, etc. which are not subjected to
heavy loading can be made accurately using powder metallurgy.
5. Products combining metals & non-metals:- Friction materials like clutch plates & brake linings
which require a metallic matrix for heat dissipation, Pb or graphite particles for smooth engagement &
silica/emery grains for creating friction.

49. 6. Products with superior qualities:- Alnico super magnets are made using powders for Al,
NI & Co. They provide very high flux densities when used in applications.
7. Others:-
Solenoid operated levers in washing m/c, bushes in motors, components of cameras,
Lead grid in lead batteries, powders for Ni-Cd batteries & fuel cells,
Uranium oxide fad rods, control rods & radiation deflectors of Zirconium, Beryllium &
Hafnium.
Fuel for rockets (Al powders)
Diamond impregnated tools, milling cutters, gear hobs, broaching tools, etc.

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