Thermo-fluid-field effects on material removal and surface integrity evolution during femtosecond laser processing of 4H–SiC: A multiscale numerical-experimental investigation

Silicon carbide (SiC) is a hard and brittle material, and its high-precision machining still faces challenges in surface integrity control. During femtosecond laser processing, local heat accumulation, melt flow, and ultrafast nonequilibrium responses induce recast layers, edge bulging, and oxygen enrichment. However, the cross-scale relationship between macroscale thermo-fluid-field evolution and microscale ablation dynamics remains unclear. This study combines multiscale simulations with experiments to investigate material removal and surface-integrity evolution during femtosecond laser processing of 4H-SiC. A finite element (FE) model incorporating recoil pressure and the Marangoni effect was established to investigate macroscale temperature evolution, melt flow, and molten-pool deformation, and to explain pit deepening, edge bulging, and recast accumulation. A molecular dynamics framework coupled with a two-temperature model (TTM-MD) was developed to simulate ultrafast electron-lattice energy transfer, lattice heating, and atom ejection, thereby providing atomistic insight into the early surface response. Femtosecond laser processing experiments were conducted under different laser powers, scanning speeds, scanning directions, and numbers of passes to investigate groove-morphology evolution and compositional changes. The combined numerical and experimental results show that nonuniform thermal loading and recoil-pressure-driven melt flow promote molten-pool deepening and recast formation, whereas higher energy input and greater pulse accumulation enlarge groove dimensions, intensify oxygen enrichment, and degrade surface integrity. This study advances the mechanistic understanding of material removal and defect formation in 4H-SiC and provides a theoretical basis for process-parameter optimization and surface-quality control, thereby supporting the further development of femtosecond laser processing for semiconductor manufacturing.