Strength and crack resistance of ceramics. Report No. 2. Silicon Nitride Ceramic

Abstract

The author reports on results of a study of the physicomechanical characteristics of a silicon nitride ceramic which can be used to make parts of gas-turbine engines and internal combustion engines. In view of features of the application of the silicon nitride ceramic, most of the attention in the study was focused on the high-temperature regions (up to 1400/sup 0/C). Statistical parameters of the strength of the silicon nitride ceramic were studied at both 20 and 1400/sup 0/C. It was possible, by the use of SPT curves, to predict the time to fracture from the prescribed load and survival probability. Delayed fracture will be seen at 20/sup 0/C only at stresses corresponding to the scatter of the breaking force under short-term loading. At the same time, at 1400/sup 0/C an increase in the time to 10/sup 5/ sec with the same survival probability causes a decrease in stress by a factor of more than twenty; i.e., delayed fracture will occur within a broad range of loads.