Additive manufacturing of TiB2 particles enabled high-performance 316L with a unique core-shell melt pool structure

Abstract

Although there have been studies reported on TiB₂ strengthened 316L via laser powder bed fusion (LPBF), none identified the decomposition of TiB₂ and the collaborative influence of titanium and boron on microstructure evolution. Here, we report a unique core-shell melt pool structure in 316L enabled by introducing 1 wt%, 2 wt% and 3 wt% TiB₂ particles through the LPBF process. In the LPBF-fabricated 316L-TiB₂ composites, the core at the centre of the melt pool contains ultrafine grains and twin boundaries while the edge features columnar grains. The TiB₂ particles undergo melting and decomposition in the steel matrix during the LPBF process as demonstrated using atom probe tomography (APT). Significant grain refinement (from 25.9 μm to about 1 μm) for LPBF-processed 316L was observed. The collaborative influence of Ti and B elements catalyses the creation of this unique core-shell structure. The LPBF-processed 316L-TiB₂ exhibits an excellent combination of high strength (yield strength: 858 MPa, ultimate tensile strength: 1095 MPa) and ductility (27%). Among the various particles evaluated, TiB₂ particles demonstrated superior efficiency over other ceramic particles in grain refinement and strength enhancement for 316L.