Hot Isostatic Pressing and High‐Temperature Strength of Silicon Nitride‐Silica Ceramics

Dense Si 3 N 4 ceramics containing 2.5 and 20 wt% SiO 2 were hot isostatically pressed by a glass‐encapsulation method. Their fracture strengths showed no degradation up to 1400°C, despite the presence of a large amount of SiO 2 glass. Moreover, in the case of Si 3 N 4 ‐20 wt% SiO 2 , plastic deformation of as much as 2.5% was observed during bending tests at the strain rate ε˙= 1.5 × 10 −4 /s. The α‐ to β‐phase‐transformation rate decreased with increasing SiO 2 content.