SECONDARY TREATMENTS OF POWDER METALLURGY COMPONENTS

1. SECONDARY TREATMENTS OF POWDER
METALLURGY COMPONENTS
Presented by
Bhukya Srinu
Reg.No:14ETMM08
M.Tech.(Materials Engineering)
School of Engineering Sciences and Technology
University of Hyderabad

2. OUTLINE
 Introduction
 Necessity
 Secondary Treatments
a) Sizing and coining
b) Machining
c) Impregnation
d) Infiltration
e) Surface engineering
f) Heat treatment
g) Joining
 Conclusion

3. Powder Metallurgy
• Powder Metallurgy is a fabrication technique involves blending and
compaction of powdered material into a desired shape, followed by a
heat treatment (sintering) to produce a component.
• Powder metallurgy is especially suitable for metals having high
melting temperatures.

4. Powder Metallurgy Process
 Powder production
 Blending or mixing
 Powder compaction
 Sintering
 Finishing Operations
4/18/2015 Powder Metallurgy

5. 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 non uniform cool-down
so the product may be repressed, coined, or sized to
improve dimensional precision.
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6. Secondary treatments:
 Sizing and coining
 Machining
 Impregnation
 Infiltration
 Surface engineering
 Heat treatment
 Joining

7. Sizing:
 Sizing is done to refine dimensional accuracy.
 Pressures used are no more than the initial compacting pressure.
 Sized parts will be straighter, dimensional tolerances will be closer and
surface finish will be improved.
 Little or no increase in density is achieved.
Coining:
 Pressures used are more than the initial compacting pressure.
 Increased part density part density in addition to improving dimensional
accuracy.
 Increased mechanical properties.

8. Machining:
Machining is any of various processes in which a piece of raw
material is cut into a desired final shape and size by a controlled
material removal process.
Machining creates geometric features that cannot be achieved by
pressing, such as threads, side holes, and other details

9. Impregnation:
 Controlled porosity permits PM parts to be impregnated with oils or resins.
 This can be done simply by submerging the PM components in an oil bath
for several hours.
 Vacuum impregnation process gives best results.
 In resin impregnation interconnected pores are filled with resins, usually
polyesters of the thermosetting type.
 This process greatly improves the machinability of PM parts by filling the
pores and increasing the density.
 Entrapment of other fluids is prevented.

10. Infiltration:
 Operation in which the pores of the PM part are filled with a molten
metal.
 The melting point of the filler metal must be below that of the PM
part.
TM (filler) < TM (Part)
 Involves heating the filler metal in contact with the sintered
component so capillary action draws the filler into the pores.
 Resulting structure is relatively nonporous, and the infiltrated part
has a more uniform density, as well as improved toughness and
strength.

11. Surface engineering:
Surface engineering refers to a wide range of technologies designed to
modify the surface properties of metallic and non-metallic components for
functional and/or decorative purposes.
Steam treatment
Coating
 Vapour deposition processes
 PVD
 CVD
Thermal spraying
Short peening

12. Steam treatment:
• In this process, all exposed surfaces are coated with hard black iron
oxide.
• Used to improve the wear properties of PM components.
• Improved corrosion resistance.
• Dimensional changes are minimal.

13. Physical Vapour Deposition:
• Deposition of a material in the vapor phase
onto a solid in a vacuum.
• The coating method involves purely physical
processes such as high-temperature vacuum
evaporation with subsequent condensation,
or plasma sputter bombardment
• Evaporated atoms travel through the evacuated
space between the source and the sample and
stick to the sample.
• Usually no chemical reactions take place
• Carried out in a vacuum atmosphere
• Used for thin and uniform coating or films

14. Chemical Vapour Deposition:
• Chemical vapor deposition (CVD) is a chemical process used to
produce high-purity, high-performance solid materials or coatings
• In a typical CVD process, the substrate is exposed to one or more
volatile precursors which react and decompose on the substrate
surface to produce the desired deposit
• Precursors include Halides (eg TiCl4), Hydrides (eg SiH4) and other
compounds etc.
• During this process, volatile by-products are also produced, which are
removed by gas flow through the reaction chamber.

15. Thermal Spraying:
• Thermal spraying is an industrial coating process that consists of a
heat source and a coating material in a powder or wire form which is
melted into tiny droplets and sprayed onto surfaces at high velocity.

16. Shot peening:
• Shot peening is a cold work process used to finish metal parts to
prevent fatigue and stress corrosion failures and prolong product life
for the part.
• In shot peening, small spherical shot bombards the surface of the
part to be finished.
• The shot acts like a peen hammer, dimpling the surface and causing
compression stresses under the dimple.
• As the media continues to strike the part, it forms multiple
overlapping dimples throughout the metal surface being treated.
• Significant improvement in fatigue properties can result from the
formation of harder and stronger surfaces.

17. Heat treatment:

18. Joining:
• Powder metallurgy itself makes it possible to obtain complex shapes,
and hence the joining operation is not often required.
• Conventional welding methods (TIG, MIG, electron beam, resistance
and friction welding) are used to join PM parts.
• Best welding results for PM steels are achieved when the component
density is 6.8 g/cm3 (88% of theoretical density) or higher.
• Sinter welding can also be done by inserting suitable powder of the
same metal between the parts to be joined, and then hot pressing
the assembly in a suitable atmosphere.

19. Conclusion:

20. References:
• Powder metallurgy science, technology and materials- Anish
Upadhyaya, GS Upadhyaya.

21. Thank you

22. Powder Metallurgy Process
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23. Finishing
• The porosity of a fully sintered part is still significant (4-
15%).
• Density is often kept intentionally low to preserve
interconnected porosity for bearings, filters, acoustic
barriers, and battery electrodes.
• However, to improve properties, finishing processes are
needed:
• Cold restriking, resintering, and heat treatment.
• Impregnation of heated oil.
• Infiltration with metal (e.g., Cu for ferrous parts).
• Machining to tighter tolerance.
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24. 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 non uniform cool-down
so the product may be repressed, coined, or sized to
improve dimensional precision.
24

25. 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
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26. 26
Densification and Sizing
Secondary operations are performed to increase density,
improve accuracy, or accomplish additional shaping of
the sintered part.
• Repressing - pressing sintered part in a closed die to increase
density and improve properties
• Sizing - pressing a sintered part to improve dimensional
accuracy
• Coining - pressworking operation on a sintered part to press
details into its surface
• Machining - creates geometric features that cannot be achieved
by pressing, such as threads, side holes, and other details

27. 27
Impregnation and Infiltration
 Porosity is a unique and inherent characteristic of
PM technology
 It can be exploited to create special products by
filling the available pore space with oils, polymers,
or metals
Two categories:
1. Impregnation
2. Infiltration

28. 28
Infiltration
Operation in which the pores of the PM part are filled
with a molten metal.
The melting point of the filler metal must be below that of
the PM part.
TM (filler) < TM (Part)
Involves heating the filler metal in contact with the
sintered component so capillary action draws the filler
into the pores.
• Resulting structure is relatively nonporous, and the
infiltrated part has a more uniform density, as well as
improved toughness and strength.