Effects of Temperature, Environment, and Orientation on the Fracture Toughness of Single‐Crystal YAG

The fracture toughness of single‐crystal YAG was measured as a function of temperature in air and under vacuum using the SENB technique up to 1600°C. The measured KIC was 2.2 MPa·m 1/2 at room temperature and it increased with temperature above 1200°C, reaching a value of 4.5 MPa·m 1/2 at 1600°C in air. The effects of crystallo‐graphic orientation and oxygen partial pressure on tough‐ness were studied at 1600°C. The toughness increased further to 5.5 MPa·m 1/2 when tested under vacuum (10 ‐5 torr)at 1600°C. Both temperature and testing environments were found to influence the fracture toughness, but there was no significant effect of crystallographic orientation.