Developing very strong texture in a nickel-based superalloy by selective laser melting with an ultra-high power and flat-top laser beam

Abstract Selective laser melting (SLM) is an important metal additive manufacturing method for manufacturing functional parts with high precision. However, the effective control of texture is very challenging for SLM, due to the use of very small heat focal point, fast scan speed, and the resulted complex thermal history. In this study, we hypothesize that the proper control of laser energy distribution using an ultra-high laser power will generate strong texture in SLMed materials. Inconel 718 superalloy is adopted as the work material, and three types of laser beams, i.e., 200 W Gaussian beam, 2 kW Gaussian beam, and 6 kW square-shaped flat-top beam, are adopted for comparison. It is found that laser beam size and energy distribution plays an important role in the solidification of metal powders. The use of ultra-high energy large-area flat-top laser beam drastically changes the grain morphology to a wide and planar geometry. Grains are elongated to millimeter-scale along the build direction, and the grain growth becomes less competitive. The grain size increases by over 150%, as compared to the case with the 200 W Gaussian laser beam. The very strong texture along the 〈100〉 crystalline direction can be obtained by using the ultra-high-energy flat-top beam thanks to a unified heat gradient direction. The local crystal misorientation and residual strain can be effectively reduced, as compared to the case with the regular 200 W Gaussian beam.