Experimental Research On The Sapphire Scratching With Single Diamond Grain

Sapphire is widely used for various applications due to its excellent physical,chemical, electrical, and optical properties. Cutting and grinding are fundamental processes for the manufacturing of sapphire in industry, and diamond abrasive tools is one of the most important manufacturing methods in use. However, the deformation and removal mechanisms of sapphire manufactured by diamond grits, especially at micron or sub-micron scales, are still to be fully understood yet.This paper aims to study the deformation and removal mechanism of sapphire crystals scratched by single diamond grit in translational, rotational, and pendulum modes. In addition, indentation tests on the A-Plane and C-Plane of sapphire crystal surface were conducted using conical tips with variable cone angles and a size few microns. Consequently, both normal force and tangential force at different scratching velocity and depth were recorded using Kistler 9119AA2 piezoelectric crystal dynamometer. in addition, the surface topographies of the scratched and indented workpieces were observed using SEM. A comparative analysis of the deformation and removal behaviors of sapphire on different crystal planes was therefore performed,and conclusions can be summarized as follows:(1) crystal structure has a significant influence on the direction of the crack generation and propagation on sapphire during indention tests. The lateral cracks were observed to preferentially generate on A-plane than C-plane of sapphire crystals and the scratching force measured on C-Plane is higher than A-Plane of sapphire crystals.(2) During scratching tests, the conical angles of the scratching tips had significant effects on the scratching force. The scratching force increases with the increase of the conical angles,(3) Scratching forces dramatically increase with the increase of scratching depth, at low scratching speed, but scratching speed has no remarkable effects on scratching forces. However, at high scratching speeds, scratching forces slightly decrease withthe increase of scratching speed.(4) At the micron scale, sapphire is of a brittle fracture mode on both A-Planes and C-Planes as indicated by the open cracks typically observed for brittle fracture and crushed sapphire powders below the diamond tips. However, on A-Plane of sapphire,a river shape of sub-cracks was observed in the plastic deformation zone; while a step shape of sub-cracks was observed in the plastic deformation zone on the C-Plane of sapphire crystal.