Characterization of carbide particle-reinforced 316L stainless steel fabricated by selective laser melting

Abstract

In this study, we have fabricated a TiC particle strengthened 316L stainless steel metal matrix composite using selective laser melting and characterized the microstructure with a particular focus on the TiC carbides in terms of their crystallography and orientation relationship with the austenitic matrix. Two families of TiC carbides are found to form in the SLM fabricated microstructure – firstly, the carbides that form along the high angle grain boundaries and secondly, those that form in the grain interior. The latter is primarily nano-crystalline TiC that are believed to precipitate out from the melt pool following a cube-on-cube orientation relationship with the f.c.c. austenitic matrix. Under this crystal registry, due to the differences in lattice parameters, a lattice mismatch between two phases occurs. The formation of TiC carbides and their morphology and distribution have been explained on the basis of melting of the powder bed under laser beam and strong melt pool dynamics during SLM process. Finally, the contribution of coherent nano-sized TiC precipitates on the overall strength of SLMed 316L-TiC metal matrix composite has been discussed wherein the TiC precipitates were found to contribute to ~50% of the strength increment in comparison to SLMed pure 316L.