THERMAL AGING BEHAVIOR OF AN SIC-FIBER REINFORCED GLASS MATRIX COMPOSITE IN A NONOXIDIZING ATMOSPHERE

The thermal aging in argon of a commercially available SiC-fiber reinf orced glass matrix composite was investigated at temperatures in the r ange 500-700 degrees C for exposure duration of up to 1000 h. An inert atmosphere was used to study the effects of temperature alone, thus m inimizing and neglecting the effects of oxidation. The mechanical prop erties of aged samples were evaluated at room-temperature by using fou r-point flexure strength and three-point flexure chevron-notch techniq ues. The inter-facial properties were determined by push-out indentati on measurements using an in-situ SEM indentation apparatus. The fractu re toughness values determined by the chevron-notch tests were little affected by the aging conditions and were in the range 19-36 h MPa roo t m. The frictional interfacial shear stress was not affected by the a ging conditions either. For the most severe aging conditions investiga ted (1000 h at 600 degrees C and 100 h at 700 degrees C), a significan t loss of flexure strength and stiffness of the samples was detected, which has been ascribed to microstructural changes that occurred in th e material during aging as a consequence of the softening of the glass matrix. At these aging conditions, a lower interfacial shear stress f or fiber-matrix debonding initiation was measured, which may be explai ned also by the occurrence of matrix softening and void formation. (C) 1998 Elsevier Science S.A. All rights reserved.