Effect of alloy composition and laser powder bed fusion parameters on the defect formation and mechanical properties of Inconel 625

The objective of this study is to determine the effects of laser powder bed fusion (L-PBF) processing parameters and alloy composition on defect formation and mechanical properties of Inconel 625 (IN625). The effects of laser power and scan speed on defect formation were evaluated for two batches of IN625 powder with slightly different compositions. Cracks were observed in all processing conditions for the powder with higher levels of Si and Nb, but not in any condition for the powder with lower Si and Nb. The elimination of cracks through composition changes led to an improvement in all tensile properties, most notably an increase in elongation from 32% to 39–48%. The effect of composition on cracking was confirmed using solidification simulations for each alloy and a numerical cracking index. Porosity was found to have a non-linear relationship with the laser scan speed for both powder batches, with large pores forming for excessively high and low speeds, due to lack of fusion and unstable melt pools, respectively. Nevertheless, samples with relative densities exceeding 99.8% were produced through the selection of suitable values for laser power and scan speed. It is concluded that porosity in IN625 is sensitive to the selection of processing parameters, while composition changes within the nominal ranges for IN625 can significantly alter the crack susceptibility of the material.