alpha/beta-sialon ceramics and its fatigue life

The investigations were focused on the phase composition, microstructure an d fatigue life of alpha/beta-sialon ceramics prepared from powder mixtures of Si3N4, AlN, Al2O3 and Y2O3 by gas pressure sintering. The results obtain ed show that the sialon ceramic material is mainly composed of 70% beta-sia lon, 30% alpha-sialon with a small amount of crystalline phase and glassy p hase at the grain boundaries. The cyclic fatigue life testings were conduct ed on Instron 8501 servohydraulic machine operating under load control, wit h a sinusoidal wave form at a frequency of 25 Hz and stress ratios (R) of 0 .1. The operations lead to the result that the fatigue limit stress is abou t 75% static strength for this material. (C) 1999 Elsevier Science B.V. All rights reserved.