MICROSTRUCTURAL CHARACTERIZATION OF SICF YMAS COMPOSITES IN THE AS-RECEIVED STATE AND AFTER THERMOMECHANICAL TESTS/

An experimental unidirectional SiC fibre-reinforced yttrium-magnesium aluminosilicate (SiCf/YMAS) ceramic matrix composite, fabricated by th e glass process, has been studied by transmission electron microscopy, high resolution electron microscopy and energy dispersive X-ray spect roscopy. YMAS matrices comprise two main phases, cordierite (Mg2Al4Si5 O18) and beta-yttrium silicate (Y2Si2O7) A continuous carbon interphas e has been observed at the fibre-matrix interface. A transition layer has also been imaged between the carbon interphase and the fibre core. This layer is believed to be a diffusion layer containing matrix elem ents except yttrium. First creep results using tensile tests in air at 1223 K are presented. Creep rates were found to be 1.1-1.3 x 10(-9) s (-1) in the 75-150 MPa stress range. Microstructural changes of the fi bre-matrix interface in samples subjected to creep and in specimens an nealed under the same conditions of temperature and time, have also be en analysed.