Study On Subsurface Damage Mechanism Of Sapphire Single Crystal Grinded By Consolidated Abrasive

Sapphire single crystal(?-Al2O3)has excellent physical and chemical properties,low manufacturing cost,easy access,and many other irreplaceable excellent characteristics.It has been widely used in aerospace,weaponry,solid-state lighting,intelligent display and so on as a valuable material for military and civilian high-tech products.Devices made of sapphire materials are susceptible to the effects of alternating load and temperature,and their working conditions are relatively bad,so the device performance and service life are closely related to the surface processing quality of the workpiece.Sapphire is a typical difficult-to-process material owing to its high hardness and brittleness.Traditional free abrasive processing of sapphire has a long processing route and high process cost.Thus it is difficult to obtain high-quality mechanically processed surfaces efficiently.Consolidated abrasive technology consolidates abrasive particles through the matrix material,which effectively improves the controllability of the abrasive processing process.Only the convex parts of the workpiece surface are cut off,and a high-quality processed surface is obtained with a small amount of material removal.In the key process of sapphire processing,the use of consolidated abrasive grinding can efficiently obtain good processing results,and the processing process is pollution-free.The grinding process can greatly reduce the surface/subsurface damage of the previous slicing process,and also determines the subsequent polishing time and cost.It has an important position in sapphire processing.Reasonably determining the subsurface damage of sapphire ground by consolidated abrasives is an important basis for formulating and optimizing the grinding process parameters.In order to reveal the mechanism of sapphire subsurface damage and reasonably determine the subsurface damage,this paper mainly carried out the following aspects of work.(1)According to the structural characteristics of diamond-consolidated abrasive pads,the theoretical model of sapphire subsurface cracks is established based on the indentation fracture mechanics theory.The results show that the crack length of the sapphire subsurface is linearly related to the cutting depth of the abrasive particles.A further model of abrasive cutting depth during the process of consolidating abrasive sapphire was found,and it was found that the average cutting depth of abrasive particles had a quantitative mapping relationship with the abrasive particle size.(2)In order to analyze the influence of the depth of the cut of the consolidated abrasive on the degree of sapphire subsurface damage.Using discrete element simulation technology,the discrete element model of sapphire is established to simulate the dynamic process of the abrasive grinding the material,and the generation and propagation of cracks between the particles of the material unit under load are analyzed.The results show that with the increase of the abrasive grain size,the crack depth and number(density)of sapphire subsurface damage increase accordingly.(3)With the help of chemical corrosion,an experimental study on the subsurface damage of sapphire ground by consolidated abrasives was carried out.In order to improve the uniformity of the workpiece corrosion,a special ceramic fixture was designed using the two-point method,which effectively improved the accuracy of the experiment.At the same time,a special jig was used to test the sapphire ground by diamond consolidation pads of different sizes,and it was found that the increase in abrasive particle size directly caused the increase of the subsurface damage layer.(4)The prediction results of the comparison corrosion experiment and discrete element simulation are consistent,which verifies the reliability of the prediction model.Therefore,the discrete element method can be used to quickly and effectively predict the number and depth of cracks on the subsurface damage layer of single-crystal sapphire polished by consolidated abrasives,and guide the optimization of polishing process parameters.