Ultrasonic vibration-assisted scratch-induced characteristics of C-plane sapphire with a spherical indenter

Sapphire, widely used in high-speed integrated-circuit chips, thin-film substrates, and various electronic components, is regarded as one of the most difficult to cut materials owing to its great hardness and low fracture toughness. Ultrasonic vibration-assisted machining (UVAM) is an effective processing method for hard and brittle materials that has been explored in many experimental and theoretical investigations. To expose the material removal mechanism in the UVAM of sapphire, the deformation features of (0001) C-plane sapphire in ultrasonic vibration-assisted scratch (UVAS) tests were compared with those in traditional scratch tests. A self-designed and manufactured spherical diamond indenter was employed. The scratch loads (i.e., the normal forces and tangential forces) were measured with a Kistler dynamometer. The plastic and brittle deformation characteristics were observed by scanning electron microscopy. Raman spectroscopy was employed to reveal the residual stress features of deformation zones in the scratch grooves. The experimental results revealed that the UVAS process can reduce scratch loads, effectively inhibit microcrack propagation, and improve the plastic removal proportion, which was rationalized with elastic and residual stress field calculations. With increasing scratch depth, the distribution of residual stress changes from tensile stress to compressive stress as indicated by the Raman-peak shift.

► We compare the features of UVAS process and traditional scratching of sapphire.
► UVAS process can reduce scratch loads and improve the plastic removal proportion.
► Residual stresses within the UVAS groove are measured by Raman spectroscopy.
► Kinematic characteristic of the diamond indenter is presented for discussion.
► Deformation features of sapphire are rationalized with stress field calculations.