In-situ synthesis of spatial heterostructure Ti composites by laser powder bed fusion to overcome the strength and plasticity trade-off

Recent research has focused on laser in-situ additive manufacturing of metal matrix composites with spatially controllable microstructures (phases). This study, inspired by the process of inserting mesh fibers into reinforced concrete, synthesizes TiN in situ using laser powder bed fusion and N2 gas. The laser-melted track, embedded with TiN particles, formed a spatially heterostructured Ti composite (SHTC) with a three-dimensional, artificially controlled architecture in a pure Ti matrix. The influences of process parameters on the mechanical properties of the spatially heterostructured Ti composite and the microstructural evolution of TiN/Ti were investigated emphatically. The results showed that the growth direction of the microstructure was changed by laser powder bed fusion additive manufacturing with alternating N2–Ar gas under suitable N2 concentration and melting track spacing. Among all spatially heterostructured Ti composites, the TiN–Ti heterolayer net-like structure achieved a high ultimate tensile strength of ∼1.0 GPa and elongation of 27 %, demonstrating a superior strength-ductility combination than intrinsic pure Ti and uniform TiN composites, as well as traditional layered structure Ti-based composites. During the tensile test, the deformation behavior was monitored in situ using digital image correlation, and the fracture mechanism was investigated. Hetero-deformation induced strengthening and toughening potentially explains the mechanism behind the strength enhancement of spatially heterostructured Ti composites. Furthermore, this work may stimulate research and development in additive manufacturing of spatial heterostructures with configurable structures, targeting synergistic regulation of strength and ductility in the integration of structure-material-function.