Hi Saurav, 

If you used any PCAs (process control agents) e.g., surfactants or lubricants during the powder blending process then any left PCAs in the powder mixtures can evolve as gases thus may evaporate during the solid state sintering process and trigger the formation of pores and defects in the microstructure. Therefore, it is suggested to use two step sintering process , i.e., raising temperature to 400-500 degrees Celsius  and hold it for 30-60 mints and then raise it to desired sintering temperature. 

Hope it helps.

Good luck,

Khurram