Abstract
Fracture toughness tests were conducted by using compact specimens of a sialon in the temperature range from room temperature to 1500°C. At elevated temperatures, a fracture initiation and a fracture resistance curve (R-curve) were evaluated by the multiple specimen method.The fracture toughness, Kc, at unstable fracture by cleavage becomes constant up to 1200°C. Then, it increases up to 1400°C. At 1500°C, the fracture occurred in a stable manner. Above 1200°C, a stable fracture by grain pull out (intergranular fracture) proceeded before unstable fracture. An area percentage of grain pull out increases with temperature rise which brings an increase in slope of R-curve. However, the fracture toghness, Kin, at the initiation of stable crack growth takes maximum at 1400°C and it decreases drastically at 1500°C. So, the viscous flow of glassy phase along grain boundary has a beneficial role on the toughness between 1200°C and 1400°C.
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