Microstructure evolution and mechanical properties of in-situ Ti6Al4V-TiB-Ti2Ni composites manufactured by laser directed energy deposition

In titanium matrix composites (TMCs), the increase in strength from the addition of ceramic reinforcement is often accompanied by a decrease in ductility. In this work, a new composite system (Ti6Al4V-TiB-Ti2Ni) has been prepared in-situ by laser direct energy deposition (LDED). Increased strength while maintaining desirable ductility and anisotropy through formation of cellular TiB and diffuse Ti2Ni nanoprecipitates. The prepared TMCs with 1 wt% reinforcement particles have an ultra-high tensile strength of 1208 MPa and an elongation of 6.9 %, which is significantly better than previously reported TMCs prepared by various processes. The role of intergranular and grain boundary TiBs in determining the mechanical properties of TMCs has been explored through in situ tensile experiments. Fundamentally, the increase in tensile strength is mainly attributed to grain refinement and load-bearing strengthening. The plasticity enhancement is attributed to Ti2Ni nanoparticles inhibiting microcracks propagation. In addition, the prepared TMCs formed a large amount of recrystallisation in the 800-1000 degrees C range, which further improved the high temperature plasticity.