Test: Powder Metallurgy - 1 - Mechanical Engineering MCQ

Powder metallurgy is the process of blending fine powdered meterials, pressing them into a desired shape or form (compacting), and then heating the compressed material in a controlled atmosphere to bond the material (sintering). The powder metallurgy process generally consists of four basic steps: Powder manufacture, powder blending, compacting and sintering. Products made by this process are very strong in compression.

Linear shrinkage is defined as ΔL/L₀, where L₀ is the original length of the part. The volume shrinkage during sintering can then be expressed as

The volume of the green compact must be larger than that of the sintered part. As mass does not change during sintering,

Powder rolling is compacting process.
There are three sintering mechanisms:
(a) solid-state bonding or diffusion
(b) vapor-phase transport or liquid phase sintering
(c) spark sintering or spark plasma sintering (SPS)

Shape index or shape factor is a measure of the surface area to the volume of the particle with reference to a spherical particle of equivalent diameter. Thus the shape factor for a flake is highest. Flake is needle like particle.

D = Diameter of compact 
P_x = Compacting pressure 
σ_r = die-wall pressure
μσ_r= Frictional stress along the die wall 
K - Inter particle friction during compaction
Balancing the vertical forces acting on the element,

If there is no friction between the particles, k = 1, 
the powder behaves like afluid, and thus  signifying a state of hydrostatic pressure.
Now, we can have the expression,

Cast cobalt alloys, also called stellites, are normally produced by the powder metallurgy method, though casting is also used by some manufactures.