The operation of heating a green compact to an elevated temperature is known as sintering. It is a process by which solid bodies are bonded by atomic forces. It is carried out below the melting temperature of the major constituent of the blended power. Most metals are sintered at 70% to 80% of the melting temperature.
Following changes occur during the process of sintering :
(i) The density of the part is increased.
(ii) Grain boundaries are formed.
(iii) Plasticity is increased.
(iv) Better mechanical interlocking is produced.
(v) Volatile materials that are present are driven off, thus producing porous product.
The sintering atmosphere is controlled to prevent oxidation of the work. The most frequently used atmosphere are dissolved ammonia and hydrogen.