Temperature Dependence of Anelastic Deformation in Polycrystalline Silicon Nitride

The influence of grain‐boundary sliding on the evaluation of the apparent Young's modulus and plastic‐deformation (flow) stress was investigated by bending tests for two types of silicon nitrides sintered with Y 2 O 3 ‐based additives The apparent Young's moduli measured at high temperatures are consistent with those predicated from a theory based on polycrystalline anelasticity due to grain‐boundary sliding. The temperature dependence of the critical bending stress for the onset of plastic deformation shows viscoplastic properties of the interglanular glass. The ductile‐to‐brittle transition of fracture is discussed by the bending strengths normalized by the measured Young's modulus.