Visualization of Subsurface Damage in Silicon Nitride from Grinding by a Plasma Etching and Dye Impregnation Method

In order to develop a spatial morphology model of subsurface damage in grinding of hot‐pressed silicon nitride, the damage has been investigated using visualization techniques, plasma etching, and a dye impregnation method developed in our previous work. The plasma etching technique resolved subsurface damage formed by a single abrasive grit on a grinding wheel surface. The damage consists of a grain‐released area, which has an overall shape approximately that of a blade like a willow leaf, and a series of bow‐like crack series that appear repeatedly along the grit‐scratching direction. By coupling these results with previous conclusions about the geometry of the strength‐controlling cracks in a flexural test specimen, we were able to develop a spatial model of subsurface damage morphology. The most distinctive feature of the model is the absence of a transverse crack, whose presence is commonly accepted in existing work on subsurface damage by grinding. The applicability of the model to the fracture behavior of a longitudinally ground flexural test specimen was verified by fractography and dye impregnation.