Investigation of molten spattering and plasma evolution in femtosecond laser ablation of superalloy
Yiwei Dong, Longfei Su, Yuting Liao, Wenlong Li, Chengping Wu, Qinqin Wang, Song Liu, Wen Guo
Abstract
The intricate coupling of multiple physical fields during ablation and the formation of micro-holes has made the use of ultrafast lasers for machining high-quality film cooling holes in nickel-based single-crystal superalloys a persistent challenge. Accurately modeling this process remains difficult. In this study, we formulate conservation equations from a fluid dynamics perspective, and employ the equivalent specific heat method to account for the latent heat of solid–liquid-gas phase transitions. The light-source equation includes the plasma shielding coefficient for a three-dimensional spatio-temporal evolution analysis of femtosecond laser ablation on superalloys. The accuracy of the numerical model is validated through experimental comparative analysis, where the simulation results are qualitatively compared with high-speed camera images of the ablation process. This comparison confirms the model’s reliability in predicting the dynamics of the process. Our findings reveal that the uneven distribution of thermal stress within the ablation crater results in increased pressure on both sides, leading to the formation of protrusions around the crater under intense stress. During the initial stages of crater formation, steam is expelled vertically upwards while also spreading across the crater walls. Additionally, the laser-induced plasma exhibits varying flow velocities at different locations, with distinct vortex phenomena observed in the top plasma. This study presents a precise numerical model for analyzing the surface quality of micro-hole formation and plasma evolution, providing valuable guidance for the application of ultrafast laser technology in high-precision micro-hole machining.