Grinding induced damage in ceramics

Although grinding is widely used as a productive technique for finishing ceramic components in the manufacturing industry, it often causes damage to the machined components. The exact nature, the manner and the penetration depth of grinding-induced damage are, however, still not clear, leaving many uncertainties and sometimes danger in using ceramics for structural applications. This paper presents research results on diamond grinding of advanced ceramics, including hot-pressed silicon nitride, hot-pressed alumina, slip-cast zirconia, and pressureless sintered silicon carbide. Grinding induced damage in these ceramics is assessed and characterized using three destructive inspection techniques and progressive lapping technique combined with scanning electron microscopy (SEM), and transmission electron microscopy (TEM). As a result, two types of grinding damage are identified, pulverization and microcracking. Damage depth is found to be related to the properties of ceramic materials, especially their brittleness. For a given grinding condition, damage penetrates deeper in less brittle materials than in more brittle materials. In addition, two types of grinding-induced microcracks are identified, scattered and clustered. The former is observed on all four types of materials tested under various grinding conditions, While the latter is only associated with less brittle materials subjected to relatively aggressive grinding conditions. The mechanisms of damage nucleation and propagation are discussed. The results provide valuable insights into the dependence of grinding-induced damage on the properties of workpiece materials, and on the grit size of grinding wheels. (C) 2002 Elsevier Science B.V. All rights reserved.