Prediction of solidification microstructures during laser dressing of alumina-based grinding wheel material

摘要

Alumina-based grinding wheels are dressed by modifying the surface of the wheels through laser surface melting and solidification with laser powers of 500 W (343 J cm(-2)), 750 W (514 J cm(-2)) and 1000 W (686 J cm(-2)) with an irradiation time of 14.4 ms. The rapid solidification rate associated with laser processing results in significant refinement of the surface grains characterized by well-defined regular facets and vertices. Such microstructures are helpful in finish/micro-scale grinding applications. In order to predict the microstructure from the laser processing parameters and the thermo-physical properties of materials, a one dimensional heat flow model is proposed. The effective thermal conductivity of the porous alumina ceramic, which is incorporated in the heat flow model, is calculated using fractal dimensions from analytical correlations. The proposed thermal model predicts the general trend of increasing melt depth with increasing laser power, which is in reasonable agreement with experimental observations. Also, the cooling rates are derived from the thermal model by calculating the values of the temperature gradient (G) at the solid/liquid interface and the velocity of the solid/liquid interface. The calculated values of the cooling rate decrease with increasing laser power in agreement with the established values in the literature. An attempt is made to correlate the observed secondary dendrite arm spacing with the calculated cooling rates.