The effect of process atmosphere on the intergranular phase in silicon nitride ceramics

The influence of the process atmosphere in the gas pressure sintering of silicon nitride has been investigated, particularly with regard to formation of the intergranular phase. The intergranular phases identified after different gas pressure sintering cycles were compared with that present in a material fabricated by the hot isostatic pressing of an identical powder composition, allowing comparison of the two processing methods. The results suggested infiltration of the nitrogen processing gas into the sintering body, which adversely affected the intergranular phase formation in a composition that had been tailored for optimal mechanical behaviour. The duration of exposure to the processing gas and the post-sintering cooling cycle were identified as being critical factors in the intergranular phase crystallisation. Copyright (C) 1996 Elsevier Science Ltd