ABSTRACT
Powder metallurgy is a process by which the metallic objects are manufactured from individual, mixed or alloyed metallic powders with or without the addition of non-metallic constituents. For that, the metallic powders are rst produced from bulk metal using different processes, then the elemental or alloy powders are mixed with additives and lubricants, and nally the powder is compacted or sintered in a punch-die set-up. For getting a goodquality product, it is essential to have suitable shape and size of powder particles and appropriate temperature and time for sintering (or compaction) pressure. The powder metallurgy process is a very suitable technique to work with refractory materials, sintered carbides and materials which are extremely difcult to machine. Powder metallurgy is also suitable for those materials which are not capable of making products by any other manufacturing method, such as diamond, cemented carbide and tungsten. In this process, the metal/alloy used in its raw form is solid which remains solid till the nal product is obtained. Thus, there does not exist any stage when the metal/alloy has to be melted. The powder metallurgy technique is mainly helpful in producing the following specialities of parts:
• Highly porous components such as self-lubricated bearings and bushes
• Composite materials such as ferrous and non-ferrous metal matrix composites
• High-performance precise components made of superplastic superalloys
• Dispersion-strengthened alloys such as W powders with thoria (ThO2) for making electric lamp laments
11.1.1 Necessity of Powder Metallurgy Methods over Conventional Production Methods
The powder metallurgy methods are necessary to carry out various processes because of the limitations of conventional processes, as follows:
1. Considerable difference in melting points of the two elements which makes them not workable together. For example the melting point of W is 3410°C and that of Al is 657°C in which one element, the Al, will become gas even before the other element W has melted.
