Effect of beam energy density characteristics on microstructure and mechanical properties of Nickel-based alloys manufactured by laser directed energy deposition

The energy density distribution directly affects the molten-pool temperature gradient, cooling and solidification rate of additive manufacturing (AM), which in turn affects the mechanical properties and microstructure of samples. In this paper, the control of the Gaussian laser beam energy density distribution characteristics is realized by controlling the defocus amount. The influence of the energy density distribution characteristics on the macro/micro structure and mechanical properties of the sample is explored. Microstructure observation and electron backscatter diffraction (EBSD) test were observed. The porosity, microhardness, tensile property, and friction of the samples were tested. These results indicated that when the beam energy density distribution was relatively uniform, the sample structure was most closely arranged equiaxed crystals. The grain size and texture strength of the samples gradually decreased, and the minimum grain size was 30.1 µm. With the energy density distribution becoming uniform, the microhardness and tensile strength first raised and fell, and the porosity and wear rate first fell and raised. The highest tensile strength was 1328 Mpa, and the smallest porosity was 0.31%. In addition, the mapping relationship between the defocus amount and the energy density distribution was deduced theoretically. Finally, combining the fine-grain strengthening and geometry necessary dislocation (GND) density, the mechanism of the effect of texture on the performance was revealed. The present work demonstrates the effectiveness of adjusting the defocus amount to control the beam energy density distribution, which in turn can effectively improve the properties of AMed metals.