Indexed on: 01 Feb '84Published on: 01 Feb '84Published in: Powder Metallurgy and Metal Ceramics
An investigation into the densification kinetics of a wurtzitelike boron nitride powder in hot pressing under high pressures has shown that under real conditions of pressing in high-pressure chambers the densification process is strongly influenced by the back pressure of desorbed gases. In the final stage of hot pressing this pressure may reach the level of the externally applied pressure and virtually stop the densification process. A rheological description of the densification kinetics of powders in hot isostatic pressing is proposed based on the volume viscous flow of a porous nonlinearly viscous solid, with allowance for the effect of the back pressure of gases trapped in pores. It is demonstrated that the proposed description makes it possible to analyze specific features of the densification of porous high-pressure phases during hot pressing. The coefficient of nonlinearity of flow established in this work has been found to be compatible with an estimated value of energy of activation in the mechanism of intergranular sliding, which is determined by the structural characteristics of wurtzitelike boron nitride particles and grains.