Optimization of Nanosecond Laser Polishing Process for TC4-B₄C Composite Material and Study on Surface Quality

To address the problem of difficult surface quality control after introducing the hard reinforcing phase into the TC4-B₄C composite material, the nanosecond laser polishing technique was employed to treat the surface of the powder-metallurgy-prepared TC4-B₄C composite material. The influence laws of laser power, scanning speed, and scanning interval on surface morphology, roughness, microstructure and surface properties were studied. With the three-dimensional surface arithmetic mean height Sa as the core evaluation index, SEM, EDS, microhardness, and XRD were combined to analyze the polishing effect and the evolution of the surface structure. The results showed that the laser power mainly affected the heat input intensity, the scanning speed mainly regulated the degree of heat accumulation, and the scanning interval determined the overlapping state of the scanning path. The three factors jointly influenced the surface remelting and recrystallization behavior. The orthogonal test results indicated that the influence order of each factor on surface roughness was laser power, scanning speed, and scanning interval; the optimal process parameters were a laser power of 30 W, a scanning speed of 750 mm/s, and a scanning interval of 0.025 mm. Under these parameters, the Sa of the sample surface decreased to 2.1 μm, which was 64.9% lower than that of the unpolished sample. Further characterization revealed that the surface roughness accumulation, pores, and irregular undulations were significantly reduced after nanosecond laser polishing, forming a relatively continuous and dense remelting layer. The microhardness increased from 704 HV to 829.3 HV. XRD analysis indicated that the surface layer after polishing was mainly composed of TiO₂, TiC, and Ti-based related phases, demonstrating that the nanosecond laser polishing mainly improved the surface quality of the composite material through surface remelting, structure reconstruction, and adjustment of the oxidation state. The research results can provide process references for the surface quality processing of TC4-B₄C and other difficult-to-machine titanium-based composite materials.