STRENGTH, TOUGHNESS AND R-CURVE BEHAVIOR OF SIC WHISKER-REINFORCED COMPOSITE SI3N4 WITH REFERENCE TO MONOLITHIC SI3N4

The flexural strength and fracture toughness of 30 vol% SiC whisker-reinforced Si3N4 material were determined as a function of temperature from 25 to 1400-degrees-C in an air environment. It was found that both strength and toughness of the composite material were almost the same as those of the monolithic counterpart. The room-temperature strength was retained up to 1100-degrees-C; however, appreciable strength degradation started at 1200-degrees-C and reached a maximum at 1400-degrees-C due to stable crack growth. In contrast, the fracture toughness of the two materials was independent of temperature with an average value of 5.66 MPa m1/2. It was also observed that the composite material exhibited no rising R-curve behaviour at room temperature, as was the case for the monolithic material. These results indicate that SiC whisker addition to the Si3N4 matrix did not provide any favourable effects on strength, toughness and R-curve behaviour.