Investigation of solidification parameters and microstructure evolution in directed energy deposition with laser beam oscillation

Abstract

Laser beam oscillation offers significant potential to enhance process stability, control solidification parameters, and tailor microstructure in directed energy deposition. A coupled mesoscopic-microcosmic numerical model is utilized in this work to investigate the effect of oscillating laser beam on the solidification parameters and microstructure evolution during the directed energy deposition with laser beam oscillation (DED-LBO) process. The dynamics solidification conditions induced by the oscillating laser beam are considered in the mesoscopic thermal-fluid model. Based on the solidification parameters, the columnar-to-equiaxed transition of the microstructure is discussed, and microstructure evolution is analyzed using the microcosmic phase-field model. The results show that temperature gradient (G) and cooling rate (GR) vary transiently with the position along the laser oscillation trajectory. The microstructure is predominantly characterized by columnar grain growth, with a relative probability exceeding 85.37 %. An increase in oscillation amplitude and frequency effectively reduces both G and GR, resulting in a coarser microstructure. Good agreement is achieved between the simulated and experimental dimensions and microstructural morphologies of the deposited layers, demonstrating the validity of the developed model. The findings of this work provide valuable insight into revealing the dynamic solidification parameters under the oscillating laser beam and elucidating the physical mechanisms governing microstructure evolution under varying oscillation conditions.