Research on the mechanism of laser removal for the oxide layer in TA15 titanium alloy by analyzing in-situ high-speed camera and product characteristics

The natural oxide film of TA15 titanium alloy hinders its serviceability for subsequent process applications. Nanosecond pulsed laser removal of oxide layers is feasible, while the nanosecond scale and high pulse number cause challenges for mechanistic studies. Therefore, we research the laser removal mechanism of the oxide layer in TA15 titanium alloy by analyzing in-situ high-speed camera and product characteristics in this paper. As the energy density (E) increases, the fluctuation degree of the molten pool intensifies. Below 17.5 J/cm2, only the molten pool and plasma variations were observed. With 17.5 J/cm2 and above, ejected block and splash occurred. As E increases, it causes the surrounding blocks to move or even "expand" before breaking. It is demonstrated the existence of the boundary between the pure thermal mechanism and the thermal-inpact mechanism between 8.75 J/cm2 to 17.5 J/cm2. The vaporization pressure was obtained by the finite difference method and the transition threshold was fitted as 14.08 J/cm2. The block ejection velocity was coincided by calculating the buckling velocity. The collection of process products also verified the in-situ camera results for the transition mechanism. Below 17.5 J/cm2, only TiO2 particles with hundred nanometer to micron sizes were collected. With 17.5 J/cm2 and above, the number of particles increased and the blocks are collected. In addition, flocculent agglomerates wrapped around particles and block agglomerates with attached particles appeared. The morphology and composition of the products were discussed with the variation of energy input.