Effect of Microstructure on Material‐Removal Mechanisms and Damage Tolerance in Abrasive Machining of Silicon Carbide

Effects of microstructural heterogeneity on material‐removal mechanisms and damage‐formation processes in the abrasive machining of silicon carbide are investigated. It is shown that the process of material removal in a conventional silicon carbide material with equiaxed‐grain micro‐structure and strong grain boundaries consists of the formation and propagation of transgranular cracks which results in macroscopic chipping. However, in a silicon carbide material, containing 20 vol% yttrium aluminum garnet (YAG) second phase, with elongated‐grain micro‐structure and weak grain boundaries, intergranular micro‐cracks are formed at the interphase boundaries, leading to dislodgment of individual grains. These different mechanisms of material‐removal affect the nature of machining‐induced damage. While in the conventional silicon carbide material the machining damage consists of transgranular median/radial cracks, in the heterogeneous silicon carbide material, abrasive machining produces interfacial micro‐cracks distributed within a thin surface layer. These two distinct types of machining damage result in a different strength response in the two forms of silicon carbide materials. In the case of the conventional silicon carbide, grinding damage results in a dramatic decrease in strength relative to the as‐polished specimens. In contrast, the ground heterogeneous silicon carbide specimens show no strength loss at all.