EFFECTS OF MICROSTRUCTURE ON THE R-CURVE BEHAVIOR OF SINTERED SILICON-NITRIDE

The R-curve behaviour of sintered silicon nitride was investigated by using short bar specimens. The samples were fabricated by sintering at 1700° C for 2 or 8 h in a nitrogen atmosphere, varying the initial α contents of the silicon nitride powder. The R-curve was evaluated with a loading and unloading technique to calculate KR during stable fracture. Steep R-curves were observed in the specimens made from the high initial α content powder. Thus, the grainbridging effect behind the crack seems to contribute to the R-curve, because a steep R-curve corresponds to fibrous texture development. Apparent Kc values with an assumption of linear elastic fracture mechanics for the specimens undergoing 8h sintering, are greater than those undergoing 2 h sintering. These results can be attributed to microcracking. © 1990 Chapman and Hall Ltd.