In-situ synthesis of high strength and toughness TiN/Ti6Al4V sandwich composites by laser powder bed fusion under a nitrogen-containing atmosphere

Laser powder bed fusion (LPBF) additive manufacturing provides the freedom to manufacture the novel bionic structures and materials with excellent mechanical properties (e.g., combining high strength and toughness). In this work, inspired by the laminar structure of natural shells, the TiN/Ti6Al4V sandwich structural materials were fabricated in the atmosphere with different ratios of nitrogen and argon. The elemental diffusion, in-situ synthesis between N and Ti atoms, microstructure evolution, and mechanical properties of LPBF-processed TiN/Ti6Al4V sandwich composites were investigated. TiN induced by the in-situ synthesis between N and Ti atoms was observed, which exhibited an excellent metallurgical bond with the Ti6Al4V matrix. The microhardness of the TiN/Ti6Al4V layer varied from 409.62 HV0.2 and 442.55 HV0.2 with different nitrogen concentrations. The tensile strength and ductility of LPBF-processed TiN/Ti6Al4V sandwich composite parts were enhanced by the combination of bio-inspired lamellar structure and internal ceramic particle reinforcement. Interlayer hard-soft phase combination in the composite parts could be contributed to the excellent mechanical properties with an ultimate strength of 1303.12 MPa and a plastic strain of 8.9%. This study demonstrates that a flexible combination of the LPBF process and reactive atmosphere can in-situ additive manufacture the novel periodic lamellar ceramic/metal heterogeneous materials with excellent mechanical performance (e.g., rigid, wear-resistant, corrosion-resistant and toughness).