Microgrinding of nanostructured materials: Experimentation and theoretical modeling

This study is aimed at experimentally investigating the effect of microgrinding on the integrity of thermally sprayed nanostructured WC/12Co and Al2 O3/13TiO2 coatings and theoretically developing a mechanical model to simulate the machining process of ceramics. A comprehensive microgrinding experiment is designed to study the effects of the grinding process parameters, such as abrasive grit size, wheel bond type, wheel depth of cut, and workpiece feedrate, on surface finish, subsurface damage, and residual stresses of these coatings. The correlation between the grinding conditions and the integrity of ground samples helps provide an experimental basis for developing a viable microgrinding technique for nanostructured materials and coated samples. A simple X-ray diffraction technique, glancing incident X-ray diffraction (GIXD), is introduced to measure the depth profiles of residual stresses in the coatings. The results of the experiment show that the effects of the microgrinding process are limited to the surface layer of ground coatings; the wheel depth of cut is the most influential parameter in the cup-type grinding; ductile flow is the dominant material removal mechanism in grinding n-WC/12Co coatings under all conditions and in grinding n-A1 2O3/13TiO2 at a low material removal rate, the residual stresses induced by the microgrinding process are compressive, strongly depend on the grinding direction, and show a strong gradient in the thickness direction for both coatings. ^ Based on continuum damage mechanics, a theoretical model is developed for predicting the behavior of ceramics under complex loadings. Unlike the linear elastic fracture mechanics, this damage model includes the effects of cracks, microcracks and inelastic deformation. The model is employed to simulate the damage development in ceramic samples during the machining process using a fourth order isotropic damage tensor. The simulated machining process is similar to the interaction between the abrasive grit and a ceramic sample in surface grinding. The final state of damage and residual stresses in the machined ceramic samples is calculated with this model. The simulation results agree well with the experimental results.