Investigation of thermal behavior of powder stream and molten pool during laser-based directed energy deposition

Abstract

Laser-powder interaction and molten pool evolution are two main physical processes in laser-based directed energy deposition (L-DED), which greatly affect the morphology and quality of the deposition layer. In this research, a comprehensive three-dimensional analytical-numerical model which integrates a laser-powder interaction model and material deposition model is developed to study the multi-physics coupling characteristics in L-DED process. The concentration of the powder stream is modeled based on conservation of mass and is in good agreement with the experimental result which is captured by high-speed camera. The effects of main parameters, including laser power, powder feeding rate, powder feeding angle and defocus length on the laser attenuation and the temperature distribution of the in-flight powder particles are analyzed. The results show that the laser attenuation rate increases from 0.72% to 1.36% with the powder feeding angle increasing from 45 deg. to 65 deg-. However, the laser attenuation rate is almost the same with the defocus length of 25 mm, 35 mm and 45 mm. Moreover, the peak powder temperature on the deposition surface increases with the increase of powder feeding angle and decrease of defocus length. Accordingly, the heat and mass input conditions at the molten pool surface for the material deposition model, including powder mass flux, effective laser intensity and powder temperature are obtained from the laser-powder interaction model. The heat transport and fluid dynamics of the molten pool are discussed based on the calculated results from material deposition model. Finally, the calculated molten pool geometry shows good agreement with the experimental results with the relative error <8.5%. This work is helpful in process optimization from the point of view of adjusting the parameters related to the powder stream and deeper understanding of laser-powder interaction and molten pool evolution during the L-DED process.