An Evaluation of Strength of Silicon-Nitride Ceramics by Means of New Test System at Elevated Temperatures

Abstract

The test system was newly developed for evaluating precisely the strength of ceramics at elevated temperatures, being equipped with the laser beam-type displacement measuring system Four-point bending tests were performed on the silicon-nitride ceramics at elevated temperatures from 800°C to 1300°C. The linear relationship held between the load, P and the displacement δ at test temperatures below 1200°C. The P vs. δ plot, however, deviated from the linear relationship at temperatures above 1200°C, suggesting the occurrence of plastic deformation. The fiexural strength remained unchanged in the test temperature range from room temperature to about 900°C and then this decreased gradually with further increase in the test temperature. The fracture toughness measured by using the Chevron notch-type specimen was nearly constant in the temperature range from room temperature to about 1100°C. The fracture toughness obtained from the Knoop-indented specimen was discussed in comparison with that from the Chevron notch-type specimen. © 1989, The Japan Society of Mechanical Engineers. All rights reserved.