Mechanical anisotropy and microstructural characterization of AISI 316LSi stainless steel using micro-plasma directed energy deposition

Directed energy deposition (DED) describes the process of depositing molten metal in wire or powder form with a focused energy beam source in a layer-by-layer fashion to create a final part. The use of an arc as heat source and wire as feedstock material for DED has become increasingly popular in recent years due to its high productivity, high versatility, availability, cost, and its ability to produce large and complex parts. However, due to the additive nature of the process and the high heat input involved, anisotropy is a recurring problem arising in printed parts, which leads to different tensile properties in the travel and build directions. In this work, the mechanical properties and microstructure of a thin-walled AISI316LSi austenitic stainless-steel component fabricated by DED using the micro-plasma arc welding (MPAW) process were analyzed. The microstructures consist mainly of austenite with fine interdendritic ferritic vertically oriented in columnar morphologies along the build direction. The effect of anisotropy was found to have a significant influence on the modulus of elasticity, with values ranging from 79.5 ± 6.8 GPa along the build direction to 105.2 ± 20.7 GPa in the travel direction. This difference was found to be due to the strong preferential orientation of grains during solidification along the <001> direction corresponding to the build direction, which was also confirmed by electron back scatter diffraction. This was confirmed by quantitatively obtaining the theoretical modulus of elasticity along the <100> direction based on the compliance coefficients, which was the main novelty of this work.