MECHANICAL-BEHAVIOR AND ENVIRONMENTAL STABILITY OF CONTINUOUS FIBER-REINFORCED GLASS-CERAMIC MATRIX COMPOSITES

The mechanical behaviour of three continuous silicon carbide fibre-rei nforced glass-ceramic matrix composites has been investigated at room and high temperatures. Commercially available composites with magnesiu m aluminosilicate, calcium aluminosilicate and barium magnesium alumin osilicate glass-ceramic matrices were considered. The materials were t ested in the as-received and aged (heat-treated in an oxidizing enviro nment) condition. Four-point bend static tests and flexural creep, fat igue and creep-fatigue tests were carried out as well as a small quant ity of tensile tests of aged composites. The experimental results have highlighted the importance of the carbon-rich layer at the fibre/matr ix interface for obtaining ''graceful'' failures. At temperatures of 7 00 to 800 degrees C oxidative degradation of the interface results in significant strength reduction and a transition to brittle fracture mo de. By rapid heat treatment of the materials at 1100 degrees C for 1 h it is possible to seal the fibre ends by forming a silica ''plug'' wh ich prevents oxygen ingress, retaining the carbon-rich interphase and composite behaviour. The results of the creep and creep-fatigue tests indicate low-cycle loading has a strong influence on the life of compo nents at high temperatures.