Solidification behavior and texture of 316L austenitic stainless steel by laser wire directed energy deposition

Abstract

The solidification behavior and crystallographic texture of 316L austenitic stainless steel builds fabricated via laser-wire directed energy deposition additive manufacturing (AM) were investigated. Shielding gas set-up and build type (single-track vs. multi-track) were varied, which led to changes in the solidification conditions and the final build compositions. Primary δ-ferrite solidification is predicted based on equilibrium thermodynamic predictions of the bulk feedstock composition. However, the increased solidification velocity of the AM process promotes a solidification mode transition from primary δ-ferrite to primary austenite. Skeletal δ-ferrite and lathy δ-ferrite associated with primary δ-ferrite solidification and interdendritic δ-ferrite associated with primary austenite solidification were observed among the laser-wire directed energy deposition walls. Skeletal and interdendritic δ-ferrite exhibited a (001)δ // (001)γ parallel relationship with austenite and a {001} solidification texture aligned with the build direction for both austenite and δ-ferrite. Lathy δ-ferrite exhibited a Kurdjumov-Sachs orientation relationship, (101)δ//(11¯1)γ, with austenite due to austenite nucleation in the solid-state. It is shown that the solidification behavior of AM 316L is accurately represented by as-built composition data and a dendrite growth model, which combined, encompasses the compositional and solidification condition impacts on the solidification pathway.