Evaluation Of Mechanical Stability Of A Commercial Sn88 Silicon Nitride At Intermediate Temperatures

Dynamic fatigue and stress rupture tests in four-point bending were conducted on a commercially available SN88 silicon nitride ceramic at temperatures in the range 700-1000 deg C in air. The objective of the study was to elucidate the failure of SN88 silicon nitride ceramic nozzles arising from a critical crack initiated at the intermediate temperature airfoil region during an engine field test. Results of dynamic fatigue tests indicated that SN88 silicon nitride tested at a stressing rate of 30 MPa/s exhibited little change in characteristic strength at the various test temperatures.