Silicon nitride compressive creep behavior in argon atmosphere

Gas pressure sintering, using pure neodymium oxide and a mixture of neodymium oxide and yttrium oxide as sintering aids, was used to process silicon nitride samples. The short-term compressive creep behavior in argon was evaluated over a stress range of 50-300 MPa, and temperature range of 1250-1400 °C. Microstructural analysis by X-ray diffractometry and transmission electron microscopy showed that secondary crystalline phases, which form from the remnant glass, are dependent upon composition and percentage of additives. Stress exponent values near to unity were obtained for lower stress and temperature testing and materials with low glass content, suggesting grain boundary diffusion accommodation processes. Cavitation will thereby become prevalent with increase in stress, temperature and amount of the grain boundary phase, and decrease in the degree of crystallization of the intergranular phase.