HIGH-TEMPERATURE ULTRASONIC CHARACTERIZATION OF THE MECHANICAL AND MICROSTRUCTURAL BEHAVIOR OF A FIBROUS COMPOSITE WITH A MAGNESIUM LITHIUMALUMINUM SILICATE GLASS-CERAMIC MATRIX

The mechanical behavior and the microstructural modifications of a SiC -fiber-reinforced magnesium lithium aluminum silicate glass-ceramic (S iC/MASL) have been characterized by ultrasonic measurement of uniaxial Young's modulus at high temperature, Under vacuum, long isothermal ag ings in the 750-1000 degrees C temperature range have shown matrix mod ifications in terms of crystallization of residual glassy phases, and of phase transformations in the Li2O-Al2O3-SiO2 system, In air, long i sothermal agings performed under the same conditions have led to the s ame matrix transformations but in competition with oxidation mechanism s of the carbon fiber-matrix interphase, All of these matrix and/or in terface transformations have been confirmed by X-ray diffraction analy sis, scanning electron microscopy, scanning acoustic microscopy, and m icroindentation tests.