A new testing device was developed to study the tensile properties of sintered silicon nitride plate specimens at room and elevated temperatures. An infrared image furnace was used to heat a specimen, and tensile tests were performed at room temperature, 1000, 1200 and 1300°C. Ten specimens were used at each temperature with the purpose of statistical analysis.
It was observed that the tensile strength decreased gradually when the temperature was raised from room temperature to 1000°C, and decreased rapidly when the temperature exceeded 1000°C. The Weibull shape parameter was in the range from 11.9 to 16.6 with an average 14.2 for the above test temperature range. At 1300°C, inelastic deformation caused by the viscosity drop of the glassy phase was observed on the load-displacement curve. Mirror-mist-hackle features were clearly observed on the fracture surfaces of specimens tested at room temperature, 1000 and 1200°C. The mirror and mist areas around the fracture origin were determined for each fractured specimen, and it was confirmed that the relation σB·r1/2=const. holds between the mirror or mist radius r and the tensile strength σB in the temperature range from room temperature to 1200°C. But at 1300°C, the fracture surface was dominated by flat and smooth region, and it was difficult to define the mirror and mist areas. Furthermore, a slow crack growth region surrounding the fracture origin was observed on some of the fracture surfaces at 1200 and 1300°C.
