Effect of laser-assisted heat treatment on material removal behavior of sapphire in indentation and scratching

Abstract

Sapphire is widely used in aerospace, microelectronics and defense applications. Due to its high hardness and low fracture toughness, it is difficult to achieve high efficiency and low damage machining. Laser-assisted machining is an effective method for machining hard and brittle materials and has been explored in many experimental and theoretical studies. In this paper, the mechanical property of sapphire and the variation of the coefficient of friction assisted by different laser powers are investigated in detail. Meanwhile, Raman spectroscopy was employed to reveal the residual stress characteristics in the deformation zone of the scratch grooves, and to analyse the changes in the depth of plastic-brittle transition of sapphire after heat treatment with different laser powers. Comparing the material removal behavior of sapphire in indentation and scratching experiments with and without laser-assisted heat treatment (LAHT), and exploring their material removal mechanisms. Experimental results show that LAHT can improve the ductility and workability of sapphire by reducing the hardness and improving the fracture behavior of the material. Hardness and elasticity modulus decrease with increasing power, and the distribution of residual stress changes from compressive to tensile with increasing power. Laser treated surface was found to possess shorter crack length, no significant localized chipping and spalling in indentation, and its scratch grooves were deeper with no radial cracks observed, the scratching force ratio was higher, the critical load for brittle-plastic transition became larger, and plastic flow lines and lumpy spalling debris appeared in the scratch areas. Nearly zero cracks were observed in material subsurface under the LAHT. With LAHT, the material is removed at a higher rate and in a more plastic way, fracture behavior of the material is improved, surface and subsurface damage is reduced, and the machining efficiency is enhanced. This study has important implications and benefits for the machining of sapphire in ensuring surface quality and achieving high efficiency.