Influence of thermal behavior along deposition direction on microstructure and microhardness of laser melting deposited metallic parts

Abstract

To have a comprehensive understanding of thermal development of a laser melting deposition (LMD) additive manufacturing process, a three-dimensional finite element model was proposed to investigate the thermal behaviors of the initial, central and terminal locations along the deposition direction of the laser-deposited tracks of Inconel 625 Ni-based alloy. The underlying influence of thermal behavior on microstructure evolution and microhardness performance in multi-track LMD-processed parts was disclosed. The simulation results showed that the heat accumulation at the initial or terminal location was more significant. The maximum cooling rate was lower and the liquid lifetime was longer at the initial or terminal location of the deposition tracks, as compared with the results produced at the central location of the track. As the dimension of the molten pool increased with the increase of the molten pool temperature, the dimension of the molten pool at the initial or terminal location was larger than that at the central location. The LMD experiments were conducted to validate the simulation. Typical dendritic columnar growth with the average primary dendrite arm spacing of 3.42 μm and 3.77 μm was observed at the initial and terminal location, respectively. In comparison, the finer columnar dendrites with the average primary dendrite arm spacing of 2.55 μm were found at the central location, due to the highest cooling rate and the shortest liquid lifetime. As a result, an enhanced microhardness (263 HV0.3) was obtained at the central location, which was apparently higher than that at the initial (241 HV0.3) or terminal (243 HV0.3) location.