The products made by powder metallurgy process are very strong in
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.
In solid-state bonding during sintering of a powder-metal green compact, the linear shrinkage is 5%. If the desired sintered density is 92% of the theoretical density of the metal, what should be the density of the green compact? Ignore the small changes in mass that occur during sintering.
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,
Sintering time is minimum for
Which of the following is not a sintering mechanism?
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)
Which of the following P/M products is made by impregnation?
Shape index is highest for
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.
Various additives, such as binders as in sand molds, are used to develop sufficient green strength and facilitate sintering in
he powder-metallurgy-operation consists of the following steps:
2. Powder production
4. Finishing operations
Arrange the above in operational seuquence:
Pressure distribution in powder compaction follows
D = Diameter of compact
Px = Compacting pressure
σr = die-wall pressure
μσr= 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,
Which one of the following cutting tool bits are made by powder metallurgy processes?
Cast cobalt alloys, also called stellites, are normally produced by the powder metallurgy method, though casting is also used by some manufactures.