Surface quality and damage mechanism of SiC in laser-ultrasonic vibration-assisted machining

Abstract

Silicon carbide (SiC), a representative third-generation semiconductor material, is widely used in semiconductor and optical applications owing to its excellent mechanical, thermal and chemical properties. However, its high hardness and brittleness make it susceptible to crack formation and subsurface damage during conventional machining. To improve machining quality and suppress brittle damage, a laser-ultrasonic composite machining method is proposed. A multiscale research framework combining molecular dynamics (MD), finite element method (FEM), scratching experiments, and turning experiments is established to investigate the material removal mechanism, brittle-ductile transition (BDT) behavior, and thermo-mechanical coupling in SiC machining. MD simulations reveal the atomic-scale evolution from plastic-dominated removal to brittle fracture with increasing scratching depth, while FEM simulations characterize stress concentration, crack initiation, and damage evolution at the continuum scale. Experimental results demonstrate that laser-induced thermal softening and surface oxidation, together with ultrasonic vibration-assisted intermittent cutting, effectively reduce machining resistance and suppress crack propagation. Compared with conventional machining, the laser-ultrasonic composite process decreases the scratching force by 71.0 % and the surface roughness by 60.9 %. Furthermore, the measured force reduction slightly exceeds the linear superposition of the reductions achieved by laser-assisted and ultrasonic-assisted machining alone, with a relative gain of 2.60 %, indicating a positive interaction trend. The critical depth of cut and BDT behavior under different machining conditions are further discussed, and an optimized processing window is identified. The proposed approach provides theoretical guidance and a feasible technological route for the high-efficiency and low-damage precision machining of SiC and other hard-brittle materials.