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 functio n of temperature in air and under vacuum using the SENB technique up t o 1600 degrees C. The measured K-IC was 2.2 MPa.m(1/2) at room tempera ture and it increased with temperature above 1200 degrees C, reaching a value of 4.5 MPa.ml(1/2) at 1600 degrees C in air, The effects of cr ystallographic orientation and oxygen partial pressure on toughness we re studied at 1600 degrees C. The toughness increased further to 5.5 M Pa.my(1/2) when tested under vacuum (10(-5) torr) at 1600 degrees C. B oth temperature and testing environments were found to influence the f racture toughness, but there was no significant effect of crystallogra phic orientation.