In-situ alloying of stainless steel 316L by co-inoculation of Ti and Mn using LPBF additive manufacturing: Microstructural evolution and mechanical properties

The grain refining impact of Ti in additively manufactured steels as well as the outstanding formability of high-Mn steels owing to their low stacking fault energy (SFE) has been confirmed in the literature. In the current work, Ti and Mn were inoculated simultaneously to the stainless steel 316 L by laser powder bed fusion (LPBF) in-situ alloying. The local accumulation of the additions developed complexes of Ti-rich brittle phases that improved strength. Microstructural observations revealed the formation of intermetallic chunks of FeTi (bcc), sigma (tetragonal), and C14 Laves phase (hcp) surrounded by emerged ferrite grains within the austenite. The rapid solidification of the molten tracks induced significant thermal stresses, which were responded by the generation of geometrically necessary dislocations (GNDs) at the austenite/ferrite interfaces, and activation of synchroshear mechanism within the Laves phase along with thermally activated slip systems in FeTi phase. Mn addition contributed to higher interface cohesion by facilitating dissociation of dislocations.