Influence of in-flight thermal dynamics of metal powder on directed energy deposition process

During the laser directed energy deposition (LDED) process, the in-flight thermal dynamics of metal powders lead to the formation of detrimental by-products such as fumes, flames, and metal vapors. In this work, we use a high-speed camera to investigate the nuanced thermal stage changes of the powders, examining how gas flow rates and laser beam powers influence them. We identify distinct stages in the powder's journey: heating up, fusion and vaporization, flaming, tailing, and accelerated falling. Notably, the latter stages adversely affect both the processing environment and surface quality. Control over gas flow rate and laser beam power dictates the trajectory, duration, and intensity of tailing. Additionally, laser irradiation accelerates the falling speed of particles by 6.8–22.8% compared to non-irradiated ones. Higher laser beam powers increase vaporization-induced propulsion, culminating in escalated particle velocities. Optimal gas flow rates enhance the surface quality by significantly minimizing high-temperature spatter. Through this work, the in-flight thermal dynamic behaviors of metal particles and their impact on LDED processing are explained.