FRACTURE AND FLEXURAL CHARACTERIZATION OF SICW SIC COMPOSITES AT ROOMAND ELEVATED-TEMPERATURES/

The fracture and flexural behaviour of monolithic SiC and SiC-whisker reinforced SiC composites (SiCwSiC) has been investigated at room and elevated temperatures, Flexure and fracture tests were conducted in a four-point beam configuration at 23 degrees C, 800 degrees C and 1200 degrees C to study the effects of whisker reinforcements especially in respect of mechanical and thermal stability at high energy environmen ts. Flexural strengths and fracture toughness data within the test tem perature range are presented in graphical as well as in Weibull form, and experimental observations are analysed and discussed, Increase in flexural strength as well as in fracture toughness has been observed w ith the whisker reinforcement. However, it was found that the trend di scontinues after a certain range of temperature. Post-failure analyses have been performed with the scanning electron microscope (SEM). Form ation of glass phase has been observed at the whisker/matrix interface and the crack growth was found to be shifting from intergranular to t ransgranular with the rise in temperature. Effects of whisker reinforc ement and the degradation of flexural and fracture properties at eleva ted temperature are investigated. Ultrasonic velocity measurements hav e been performed through the thickness of the untested as well as frac tured specimen, and the variation in the sonic wave velocity is discus sed in this paper.