Tensile Test of Sintered Silicon-nitride Ceramics at Elevated Temperatures

Abstract

The test system was newly developed for evaluating precisely the tensile strength of ceramics at elevated temperatures. Four-point bending and tensile tests were performed on the sintered silicon-nitride ceramics in the temperature range from room temperature to 1300°C. The track of ductile fracture was observed on the fracture surface of tensile specimen tested at temperatures above 1100°C, suggesting the occurrence of plastic deformation. Fracture stress of bending specimens was about 1.18∼1.43 times as large as that of tensile specimen. The test temperature dependency, however, was very similar in both the fracture Stresses in the whole test temperature range. The fracture toughness from tensile and bending specimens were almost the same in the test temperature range from R. T. to about 800°C. The fracture toughness obtained from the chevron notch-type specimen was almost coincident with that from the Knoop-indented specimen in the temperature range from R. T. to 900°C. They, however, produced some difference in the temperature above this, suggesting occurrence of the adhesion at the crack tip in the Knoop-indented specimen.