Influence of wall thickness on microstructure and mechanical properties of thin-walled 316L stainless steel produced by laser powder bed fusion

Abstract

Laser powder bed fusion (L-PBF) allows for the fabrication of samples with complex geometries based on thin struts or walls. However, only few studies have focused on the effect of these geometries on the properties of the material fabricated using this technology. In this work, we studied the impact of wall thicknesses below 1 mm on microstructure formation and mechanical properties in 316L parts fabricated by L-PBF. The size and geometry of melt pools varied significantly between different wall thicknesses due to powder denudation and local preheating, resulting in non-symmetrical melt pools for thicker samples. Furthermore, in the sub-grain microstructure, the thinnest samples consisted of solidification cells oriented almost parallel to the building direction. In the thicker walls, side branching and slender columnar grains were observed in the center lines of the melt pools. On the grain size scale, the thinnest samples consisted of finer grains with a more pronounced texture 〈100〉, while large grains growing parallel to the build direction and texture 〈101〉 were found for the thicker samples. Mechanical tests showed that the strength and ductility were higher in thicker samples, which was attributed to finer solidification cells.