GRINDING FORCE AND MICROCRACK DENSITY IN ABRASIVE MACHINING OF SILICON-NITRIDE

The relationship between grinding forces and the material's resistance to microfracture is investigated in abrasive machining of silicon nit ride ceramics. Surface grinding is performed on two forms of silicon n itride with different microstructures, and the grinding forces are mea sured. In addition, single-point scratching is performed on polished s urfaces to amplify the damage associated with the action of an individ ual abrasive particle in grinding. A thermal wave measurement techniqu e is then used on the cross sections to characterize the density of su bsurface microcracks associated with scratching. Compared to a fine-gr ain silicon nitride, the density of microcracks in a course-grain sili con nitride is significantly larger, while the grinding force is small er. The smaller grinding force for the coarse-grain silicon nitride is attributed to the ease of local intergranular microfracture and grain dislodgement during grinding.