a) Particle shape :- It may be flat, angular, dendritic, spherical or ragged, depending upon the method used for its production to effects compactness, porosity and strength of the part. Ans. The principal characteristics of metal powders who make them suitable for powder metallurgy processes are as follows
b) Particle size and distribution :- It has an appreciable influence over compressibility, density, porosity and also shrinkage during sintering. Use of particles of similar size increases porosity and of dissimilar size decrease it. Use of all coarse grains reduces density, but needs greater briquetting pressures. Thus, a balanced proportion of different particles sizes has to be worked out.
c) Apparent density :. It is the specific gravity of the powder Any reduction in it will call for the use of more powder, and hence it should be maintained constant so that the same quantity of powder is required for each part. By controlling it properly, one portion of a component can be made harder and denser than the remaining portion.
d) Flow rate or flow-ability :- It is this property which enables a powder to flow readily and fill the mould cavity. It governs the time required to fill a mould and the rate of production.
e) Compatibility : It is governed by the shape and particles sizes distribution of the powder. It is the ratio of the initial volume of the powder to the final volume after compression. It governs the green strength of the powder, that is the mechanical strength of compressed part before sintering, and this factor is of great importance for easy handling of parts during the operations.
f) Purity presence of impurities adversely affects the briquetting and sintering processes, reduces the life of dies by causing wear and lowers their mechanical properties Purity of powder is of great importance as
g) Sintering ability successful production of parts. It should be sufficiently high for successful production of part
h) Chemical composition.
