TiC reinforced Ti6Al4V fabricated by circular oscillating laser directed energy deposition: Microstructure and wear resistance

Gaussian laser is a common laser source in the field of laser directed energy deposition (L-DED). However, Gaussian laser sources have certain limitations, as they produce elevated temperature differentials and internal stresses during L-DED, which can result in significant distortion and fracturing. To address these restrictions, this research proposes using a circular oscillating laser as the energy source for L-DED. TC4 deposition samples and 5 wt% TiC/TC4 composite deposition samples were prepared using both Gaussian laser directed energy deposition (GL-DED) and circular oscillating laser directed energy deposition (COL-DED), and the deposition samples prepared under the two laser modes were compared and studied. The results indicate that, in the process of COLDED, the laser oscillates periodically at a constant frequency in the high-temperature molten pool, which produces a more consistent temperature gradient and improved stirring effect in the molten pool. This inhibits grain growth and effectively refines the grains. Compared to the TiC/TC4 deposition samples prepared with Gaussian laser, the average grain size of COL TiC/TC4 deposition samples decreased by approximately 54.3 %. Due to the effects of the high-power laser beam, TiC particles partially melted and decomposed into Ti and C. As the laser advanced, the molten pool cooled swiftly, ultimately precipitating uniformly distributed gray-white TiC hard phases. Compared to the TC4 alloy prepared with the Gaussian laser, the TiC/TC4 composite material manufactured with a circular oscillating laser exhibited a 24.5 % increase in microhardness (430.76 HV0.2) and a reduction in wear rate of approximately 42.15 % (to 1.4 x 10-6 g/mm). Circular oscillating laser directed energy deposition can, to a certain extent, improve the hardness and wear resistance of materials compared to Gaussian laser directed energy deposition.