Material removal and damage formation mechanisms in grinding silicon nitride

Abstract

Surface grinding was performed on two silicon nitrides with different microstructures. The ground surfaces of both materials were observed with scanning electron microscopy (SEM) to consist of areas of microfracture, smeared areas, and areas covered with fine debris particles. It was determined that microfracture is the primary mechanism for material removal. Subsurface grinding damage was revealed by a bonded-interface technique to take the form of median-type cracks extending from the plastic zones. Distributed intergranular microcracks and intragrain twin/slip bands were observed within the plastic zones. The strengths of transverse-ground specimens were measured in four-point flexure. For the silicon nitride with a fine grain size and a mildly rising toughness-curve, grinding damage resulted in a drastic strength degradation compared to polished specimens. In contrast, the silicon nitride with large and elongated grains and a steeply rising toughness curve showed relatively little strength loss. The relationship between the ceramic microstructure and the damage tolerance in abrasive machining is discussed in light of these results.