Effects of Grain Size of Hot‐Pressed Silicon Nitride on Contact Damage Morphology and Residual Strength

Abstract

Effects of the grain size of hot‐pressed Si3N4 on contact damage morphology and residual strength were studied using the elastic/plastic indentation method with a spherical indenter. The contact damage, initially formed with increasing indentation load, was Hertzian cracks in the Si3N4 consisting of fine grains (mean grain size: 0.2 μm). In the coarser‐grained Si3N4 (mean grain size: 0.8 μm), there was a damage texture, consisting of grain‐sized microcracks. The residual strength was degraded at a load slightly higher than the critical load for contact damage formation. The strength degradation was not caused by contact damage but the residual stress formed around the impressions.