Toughness Properties of a Silicon Carbide with an <i>in Situ</i> Induced Heterogeneous Grain Structure

Abstract

Toughness characteristics of a heterogeneous silicon carbide with a coarsened and elongated grain structure and an intergranular second phase are evaluated relative to a homogeneous, fine‐grain control using indentation–strength data. The heterogeneous material exhibits a distinctive flaw tolerance, indicative of a pronounced toughness curve. Quantitative evaluation of the data reveals an enhanced toughness in the long‐crack region, with the implication of degraded toughness in the short‐crack region. The enhanced long‐crack toughness is identified with crack‐interface bridging. The degraded short‐crack toughness is attributed to weakened grain or interface boundaries and to internal residual stresses from thermal expansion mismatch. A profound manifestation of the toughness‐curve behavior is a transition in the nature of mechanical damage in Hertzian contacts, from classical single‐crack cone fracture in the homogeneous control to distributed subsurface damage in the heterogeneous material.