Numerical simulation for the evolution in surface morphology of titanium alloy by nanosecond pulsed laser ablation

Abstract

Lack of effective methods to investigate the evolution mechanism of crater and stripe morphology formed on the surface of titanium alloy by nanosecond pulsed laser. In this paper, the evolution of the surface morphology of titanium alloy during laser ablation was elucidated by numerically simulating the temperature and flow fields of multiple nanosecond pulsed lasers. With 8.75 J/cm2 and 35 J/cm2, uniform crater morphology and stripes shape were formed respectively, but the surface roughness increased. In the former case, the surface of the melt pool was depressed by the vaporization pressure, and the rapid solidification caused the edge of the supercooled crater to increase, forming crater morphology. In the latter case, the difference is related to the formation of multiple relatively independent melt pools at lower energy input, where the heat accumulation caused multiple molten pools to merge into a large-scale molten pool. The flow velocity increased, the molten pool duration was prolonged and the size of the molten pool increased, resulting in a triangular-trapezoidal-tower trend of the pit edge. The size of the pit edge decreased or even “disappeared”, eventually forming stripes shape.