Tensile behaviour of gas pressure sintered silicon nitride in the 1600-1700 degrees C temperature range

The tensile behaviour of a silicon nitride ceramic has been studied between 1600 and 1680 degreesC under strain rates from 6x10(-6) to 1.2x10(-5) s(-1 ). At low temperature and/or high strain rate, the behaviour was essentiall y brittle: failure occurred by cavitation along boundaries of acicular grai ns lying normal to the tensile axis arid linking of these cavities by inter facial debonding. At 1650 degreesC, the deformation started to be ductile: a stress peak was observed in the tensile curve and cavities formed at mult igrain junctions while grain boundary sliding began to occur. As the temper ature increased. the contribution of grain boundary sliding to deformation increased at the expense of the cavitational component. The stress peak is interpreted in terms of a relaxation effect that governs the competition be tween cavitation and grain boundary sliding. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.