A novel Al2O3/SiO2 core–shell composite abrasive was successfully synthesized via a facile sol–gel strategy and utilized to promote the surface quality and polishing efficiency of sapphire wafer. The silica shell with dense and amorphous structure was successfully coated on Al2O3 core. Its synthesis mechanism was discussed deeply, and good dispersibility and uniform particle size were obtained. The acquired core–shell composite particles were employed for the planarization machining of sapphire wafer. Results show that the decrease in surface roughness of Al2O3/SiO2 core–shell composite abrasives during polishing is more than 20.2% of that of pure Al2O3 abrasives, the material removal rate is more than 5.1% of that of pure Al2O3 abrasives, and the residual stress of the sapphire wafer finished by composite abrasives is decreased by approximately 40%. These results demonstrate that the Al2O3/SiO2 core–shell composite abrasives provide a more excellent polishing performance for the sapphire wafer, resulting in smoother and scratch-free surface with a higher material removal rate compared with pure Al2O3 abrasives. On the basis of the reaction product analysis and elastic-plastic micro-contact mechanics, the reasons for the improvement of polishing performance were revealed in terms of chemical corrosion and mechanical abrasion.
Corrosive and toxic solutions are normally employed to polish sapphire wafers, which easily cause environmental pollution. Applying green polishing techniques to obtain an ultrasmooth sapphire surface that is scratch-free and has low damage at high polishing efficiency is a great challenge. In this paper, novel diamond/SiO2 composite abrasives were successfully synthesized by a simplified sol-gel strategy. The prepared composite abrasives were used in the semi-fixed polishing technology of sapphire wafers, where the polishing slurry contains only deionized water and no other chemicals during the whole polishing process, effectively avoiding environmental pollution. The experimental results showed that diamond/SiO2 composite abrasives exhibited excellent polishing performance, along with a 27.2% decrease in surface roughness, and the material removal rate was increased by more than 8.8% compared with pure diamond. Furthermore, through characterizations of polished sapphire surfaces and wear debris, the chemical action mechanism of composite abrasives was investigated, which confirmed the solid-state reaction between the SiO2 shell and the sapphire surface. Finally, applying the elastic-plastic contact model revealed that the reduction of indentation depth and the synergistic effect of chemical corrosion and mechanical removal are the keys to improving polishing performance.
By using a resin bonded diamond grinding wheel, the influence of grinding conditions on processing quality of the ultrafine cemented carbides with different Co content were investigated. Through grinding experiments, the effects of grinding wheel linear speed, feed speed and grinding depth on the surface morphology, roughness, and residual stress of cemented carbides were studied, and the relationship between grinding conditions and machining quality was established. Then, the evaluation and prediction of surface quality according to the grinding parameters can be realized by using ternary regression analysis. Finally, gray relational analysis was applied to optimize the multi-objective concerning surface quality to find the optimal grinding process parameters. The grinding test results show that with the increase of grinding linear speed as well as the decrease of feed speed and grinding depth, the maximum undeformed abrasive particle thickness decreases, which improves the surface plastic removal ratio and reduces the surface roughness. The multi-objective optimization of the grinding process can be achieved by using gray relational analysis, the resulting optimal process parameters achieve the lowest residual stress and surface roughness, which provides a theoretical basis for the prediction and control of the surface quality of cemented carbide in the grinding process.
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