The role of the solidification structure on orientation-dependent hardness in stainless steel 316L produced by laser powder bed fusion

Abstract

Owing to the rapid cooling rates and directional thermal gradients involved, fusion-based additive manufacturing (AM) processes yield complex, fine solidification structures that impart anisotropic mechanical properties in materials, such as stainless steel 316L (SS316L). In this work, we present a comprehensive study of the mechanical anisotropy of SS316L produced by laser powder bed fusion using instrumented nanoindentation. We produce and test near-single crystal samples oriented along the three principal crystallographic axes—namely ⟨100⟩, ⟨110⟩, and ⟨111⟩—using a Berkovich indenter. We find that the ⟨111⟩ and ⟨100⟩ orientations exhibit the highest and the lowest hardness, respectively. To decouple the contributions of grain orientation and solidification structure to the alloy's mechanical anisotropy, we compare our experimental results against crystal plasticity finite element (CPFE) simulations. We ascribe the hardness anisotropy in SS316L to the cell spacing along the slip direction (CSSD), which is a novel metric that we introduce to account for the role of the solidification structure on plasticity. Our work provides a universal pathway to understanding the microstructure-property relationships in cubic metallic materials that exhibit solidification structures,such as those commonly imparted by fusion-based AM.