WHISKER REINFORCEMENT OF GLASS-CERAMICS

Silicon carbide whisker reinforcement of anorthite and cordierite glass ceramics has been studied. At 25 vol% whisker loading the flexural strengths increased from 65-103 MPa to 380-410 MPa, the fracture toughnesses increased from 1.0-1.5 MPa m1/2 to 5.2-5.5 MPa m1/2. The strengths decline to 240-276 MPa at 1200-degrees-C. The reasons for the decrease in strength with temperature are discussed. Whiskers from two different sources with differences in diameters and aspect ratios were evaluated and the effect of the whisker morphology on the composite properties was studied. It was found that larger diameter, higher aspect ratio whiskers result in improved composite performance. The composites were also characterized in terms of their thermal properties, i.e. thermal expansions and thermal conductivities. The thermal expansion coefficient from 25-1000-degrees-C for anorthite-based composite was 4.6 x 10(-6)-degrees-C-1 and that for the cordierite-based composite was 3.62 x 10(-6)-degrees-C-1. The thermal conductivities at 1000-degrees-C were 3.75 and 4.1 W m-1 K-1 for cordierite and anorthite composites, respectively.