Significance of powder feedstock characteristics in defect suppression of additively manufactured Inconel 718

The characteristics of powder applied in electron beam powder-bed fusion (EB-PBF) play a vital role in the process stability and final part performance. We use two types of Inconel 718 alloy powders for experiments, namely, (i) imperfect spherical and (ii) spherical powders. They have similar particle size distributions but are different in geometry and built-in defect. The forming qualifies concerning surface topography, density, and internal defect of the EB-PBF-built samples prepared using two types of powders are characterized under the same processing conditions. In particular, the forming qualifies are further compared under the optimal process condition to highlight the decisive role of powder features. Notably, different powder geometries with distinct surface feature inevitably affect the heat transfer during melting. The significance of powder feedstock characteristics in defect suppression is clarified with the aid of numerical simulations. The experimental results show that compared to spherical powders, fabrication using imperfect spherical powders is more likely to evoke lack-of-fusion and excessive melting under low and high energy conditions, respectively. Thus, spherical powders have a broader process window in ensuring a higher density and smoother surface than that of imperfect spherical powders. Moreover, in the sample built with spherical powders, the high cooling and solidification rates evaluated by numerical simulations result in the suppression of the interdendritic voids.