The effect of lubricants in single point scratching and abrasive machining of alumina and silicon nitride

The machining of ceramic materials is fraught with subsurface damage and low material removal rates because of their high hardness, low thermal conductivity and brittle behavior. With this in mind, the subsurface damage and material removal in single point scratching and abrasive machining of alumina and silicon nitride were studied. The lubricants were selected based on their potential for high material removal rates and low subsurface damage as determined from an earlier study. A Vickers pyramidal indenter with a linear transverse motion was used for scratch tests while abrasive machining was done under controlled load conditions in a modified belt sander. The material removal rates in scratch tests was determined by profilometry and in abrasive machining by gravimetric measurements. The subsurface damage was studied by scanning electron microscopy (SEM). It was found that the subsurface damage in both processes was greater in alumina than in silicon nitride. The lubricants were found to contribute to higher material removal rates and lower subsurface damage as compared to the dry condition. X-ray photoelectron spectroscopy (XPS) analysis of the abrasively machined surfaces of alumina revealed that the compounds such as Al(OH)3 and MeSiO5 were generated on the cutting surfaces. These compounds contributed to the above effects by making the cutting conditions less aggressive.