Influence of diameter and scan strategy on the geometrical, microstructural, and mechanical properties of small Inconel 625 L-PBF struts

Abstract

The geometries, microstructures, and mechanical properties of vertically built Inconel 625 Laser Powder Bed Fusion (L-PBF) struts were investigated in this study. The influence of strut size (between 0.2 mm and 2 mm) and scan strategy was more specifically addressed. As-built struts exhibit satisfactory geometry and porosity rates, whatever the strut size and scan strategy. Classical columnar grains oriented parallel to the build direction (BD) were obtained, with a < 001 > // BD fiber texture only for the smaller struts (0.2 mm to 0.5 mm), due to the formation of a unique circular melt pool on the whole strut surface. At a smaller scale, the influence of the build strategy is also visible on solidification cells, whose average diameter decreases for outside-in strategies and larger hatching area ratios. The tensile strengths and hardness values are lower for the smaller diameter (0.3 mm) struts and for the inside-out strategies, suggesting the important role played by a finer sub-grain structure and a smaller crystallographic texture on the strengthening of Inconel 625 struts.