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Consider the following statements regarding powder metallurgy: 1) Refractory materials made of tungsten can be manufactured easily. 2) In metal powder control of grain size results in relatively much uniform structure. 3) The power heated in die or mould at high temperature is then pressed and compressed to get desired shape and strength. 4) In sintering, the metal power is gradually heated resulting in coherent bond. Which of the above statements are correct?

Consider the following statements regarding powder metallurgy: 1) Refractory materials made of tungsten can be manufactured easily. 2) In metal powder control of grain size results in relatively much uniform structure. 3) The power heated in die or mould at high temperature is then pressed and compressed to get desired shape and strength. 4) In sintering, the metal power is gradually heated resulting in coherent bond. Which of the above statements are correct? Correct Answer 1, 2 and 4 only

Powder metallurgy is a process in which metallic powders are heated below their melting temperatures to achieve bonding.
It involves metal or alloy powders to be compacted into the desired shape after blending, and then to be heated in a controlled atmosphere at a temperature below their melting points in order to achieve bonding of the particles to get the desired properties. The powder metallurgy process enables to produce parts in their final shape, thus eliminating the need for any additional machining. Refractory materials can also be converted into powder and can be given any shape. 

Basic steps of the manufacturing of parts by powder metallurgy are

  • Production of metal powders
  • Blending and mixing of powders
  • Compaction
  • Sintering
  • Finishing operation

 

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Production of metal powders: Production of metal powders is the first step in powder metallurgy, there are various techniques to produce the metal powders. The more uniform grain will result in a more uniform structure. 

Blending and Mixing: In this process, metallic powders in the required proportion are mixed uniformly. Binders are added to develop the required green strength. Lubricants are added to reduce interparticle friction and to reduce die wall friction.

Compacting: In compacting, loose powder is compressed into a shape known as a green compact, which is a very important step in powder metallurgy. The desired characteristics to be achieved by compacting are high product density and uniformity of that density throughout the compact.

Sintering: Sintering is the process of heating the green compact at a high temperature below the melting point in a controlled atmosphere. Sintering increases the bond between particles and increases the strength of the powder metal compact.

Secondary Operations: Generally, some optional Secondary Operations are performed on the sintered part to achieve the final dimensions and properties of the part. Example: Repressing, Sizing, Coining, Heat treatment, Finishing operations.

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