MACHINING AND SURFACE FINISHING OF BRITTLE SOLIDS

Ceramic materials are finished primarily by abrasive machining process es such as grinding, lapping, and polishing. In grinding, the abrasive s typically are bonded in a grinding wheel and brought into contact wi th the ceramic surface at relatively high sliding speeds. In lapping a nd polishing, the ceramic is pressed against a polishing block with th e abrasives suspended in between them in the form of a slurry. The mat erial removal process here resembles three-body wear. In all these pro cesses, the mechanical action of the abrasive-can be thought of as the repeated application of relatively sharp sliding indenters to the cer amic surface. Under these conditions, a small number of mechanisms dom inate the material removal process. These are brittle fracture due to crack systems oriented both parallel (lateral) and perpendicular (radi al/median) to the free surface, ductile cutting with the formation of thin ribbon-like chips, and chemically assisted wear in the presence o f a reactant that is enhanced by the mechanical action (tribochemical reaction). The relative role of each of these mechanisms in a particul ar finishing process can be related to the load applied to an abrasive particle, the sliding speed of the particle, and the presence of a ch emical reactant. These wear mechanisms also cause damage to the near c eramic surface in the form of microcracking, residual stress, plastic deformation, and surface roughness which together determine the streng th and performance of the finished component. A complete understanding of the wear mechanisms leading to material removal would allow for th e design of efficient machining processes for producing ceramic surfac es of high quality.