Material removal and subsurface damage studies in dry and lubricated single-point scratch tests on alumina and silicon nitride

The grinding of ceramics is an extremely expensive yet unavoidable process. This fundamental study was inspired by this need. The objective was to examine how the lubricants, that have been reported to contribute to high wear in normal tribological testing, contribute to material removal in single-point scratch tests which may be the basis of grinding. The material removal and subsurface damage in single-point, unidirectional scratch tests on alumina and silicon nitride in the dry and lubricated conditions were studied. The lubricants used were distilled water, tricresyl phosphate (TCP), mineral oil, cutting oil, NH4OH, and mineral oil with 1 wt.% of the following additives: chlorinated fatty acid, chlorinated fatty ester, chlorinated paraffin, and sulfurized lard oil. The material removal rate was found to be proportional to the load squared and was higher in alumina than in silicon nitride. The material removal rate was the highest in water for alumina and in mineral oil for silicon nitride. Water lubrication reduced the damage in silicon nitride but it promoted stress corrosion cracking in alumina under high loads. When scratching was done in NH4OH, the material removal rate in alumina was fairly high because of stress corrosion cracking. With TCP lubrication, the material removal rates in both ceramics were fairly high and there was no subsurface damage. The other organic lubricants led to lower material removal rates and little or no subsurface damage in both ceramics. (C) 1999 Published by Elsevier Science S.A. All rights reserved.