Effects of the deflection angle of the indenter on the material removal and damage evolution of fused silica during scratching

Abstract

Fused silica is widely used as key optical components and window materials due to its excellent optical and thermal properties. However, surface and subsurface damages occur in fused silica during the machining and usage process. This study aims to investigate the influence of the deflection angle of Vickers indenter on the damage evolution and removal mechanism of fused silica during scratching. Scratch tests with a linearly increasing axial load were conducted under four typical deflection angles (0°, 15°, 30°, and 45°). The resultant surface morphologies of scratch grooves were analyzed. It was seen that as the axial load increased, the scratch groove transformed from ductile deformation to brittle breaking. The asymmetric placement of the indenter led to asymmetric crack expansion. As the deflection angle increased, it became increasingly difficult to form a stable groove on the material surface. Among the four deflection angles, the groove at 0° was symmetrical, with long and good quality ductile area. For the deflection angle of 30°, the widest range of chips was observed; for 45°, the contact area of the indenter with the material was minimized, and specifically, there was a situation where the bottom of the groove was higher than the reference plane. Furthermore, statistical analysis of the loads during the scratching process was carried out. As the axial load increased, the lateral load increased approximately linearly at first and then fluctuated dramatically. Furthermore, under relatively small axial loads, the coefficient of friction (COF) is lower when the deflection angle is small; while, under relatively high axial loads, the COF is larger when the deflection angle is small. This transition could be related to the change in material removal mode from completely ductile removal to the brittle dominated removal.