Femtosecond laser surface modification of 4H-SiC improves machinability

The high brittleness and hardness are harmful to the machinability of silicon carbide (SiC). To improve machinability, femtosecond laser (fs laser) surface modification was conducted. The results of scratching test for modification surface showed the fluctuation of tangential force and coefficient of friction (COF) and the decrease of energy of acoustic emission peak. COF under various axial loads tends to be 0.2. The scratching profile has a conformal shape and deeper depth. Experiments elucidate that machinability is improved by fs laser surface modification due to surface decomposition and laser-induced periodic surface structures. Although fs laser processing was treated as cold processing to some extent, the heat-related phenomena were non-negligible in SiC processing. To reveal the dynamic multi-scale mechanism during fs laser modification, the multi-physics finite element model and the molecular dynamics simulations coupled with a two-temperature model were applied. Multi-scale simulation results revealed that the recoil flow has a high speed of >1.2 m/s and the peak temperature exceeds 8000 K, causing the spatter and heat affect zone. The high electronic temperature gradient is generated during irradiating, causing the subsurface void generation. Consequently, fs laser surface modification can improve machinability, but the heat effect and subsurface void should be cautioned.