Title

Abrasive machining of ceramics: Assessment of near-surface characteristics in high-speed grinding

Date of Completion

January 2000

Keywords

Engineering, Mechanical|Engineering, Metallurgy

Degree

Ph.D.

Abstract

This dissertation focuses on two important issues in abrasive machining of ceramic materials: (i) improvement of grinding performance and (ii) characterization and assessment of grinding-induced damage in the near-surface region of ground ceramic workpieces. Standard bending test bars of hot-pressed silicon nitride and sintered aluminum nitride were used in this work. Regarding the first issue we studied the feasibility of high speed grinding as a means of attaining a high material removal rate while minimizing grinding damage for ceramic materials. It was found that surface roughness of ground ceramic workpieces decreases with increased wheel speed. The retained strength of ground ceramic workpieces was observed to increase with increased wheel speed. In addition, an order of magnitude analysis of the specific grinding energy was performed to provide an insight towards high speed grinding mechanisms for ceramic materials. The energy analysis indicated that most of the specific energy expended in high speed grinding of ceramic materials is associated with plowing and cutting by ductile flow. ^ In regard to the second issue we employed grazing incidence x-ray diffraction to examine near-surface distributions of residual stress and microstrain, i.e., microplastic deformation, in machined silicon nitride workpieces. It was found that grinding-induced residual stress is compressive in the outer surface layer and becomes tensile with increasing distance from the surface for all grinding conditions studied. The thickness of the compressive layer was observed to decrease with increased wheel speed. It was found that the surface microstrain for the silicon nitride ground at high wheel speeds is greater than that for the silicon nitride ground at low wheel speeds. We also investigated the implications of the characteristic near-surface microstrain, represented by deformation depth, on assessment of grinding damage in terms of effective crack depth. This study revealed a linear relationship between the effective crack depth and the deformation depth. Consequently, we can estimate the retained flexural strength of ground silicon nitride from experimentally measured microstrain. A methodology for the prediction of flexural strength of machined silicon nitride is presented. ^