Fracture toughness, strength and creep of transparent ceramics at high temperature

Fracture toughness, four-point bending strength of transparent spinel, Y2O3 and YAG ceramics in function of temperature (from room temperature up to 1500°C) were measured. Creep resistance at 1500–1550°C was studied too. Grain size distribution was determined on polished and etched surfaces of samples. Fracture surfaces after tests were examined by scanning electron microscopy. The obtained results showed that: in the case of spinel ceramics fracture toughness and strength decreased from 20 to 800°C, increased from 800 to 1200°C and decreased at higher temperature; in the case of Y2O3 ceramics they increased from 400 to 800°C, and next kept constant up to 1500°C; in the case of YAG ceramics they kept constant from 20 to 1200°C and then decreased. The creep strain rate was measured for spinel and YAG but not for Y2O3 ceramics which appeared creep resistant. The hypotheses concerning toughening and creep mechanisms were proposed.