Construction of three-dimensional network morphology titanium matrix composites via adding nano B4C: As-built and heat-treated scenarios

Abstract

This study examines the role of nano B4C addition in improving the mechanical properties of Ti–6Al–4V (Ti64) alloys fabricated by laser melting deposition under as-built and heat-treated conditions. However, the enrichment of reinforcing phases generated by in situ production at grain boundaries causes a serious reduction in ductility, limiting the development of high-performance titanium matrix composites. To avoid this deficiency, the fabricated titanium matrix composites (TMCs) were subjected to three different heat treatment programmers, namely, subtransus heat treatment, supertransus heat treatment and triple heat treatment. The effects of B4C addition and heat treatment on microstructure, texture and mechanical properties were systematically investigated. The results show that TiB and TiC, synthesized in situ, promote the precipitation of α-Ti with a non-Burgess orientation relationship, and weakening the texture intensity of α-Ti. The ultimate tensile strength of the in situ synthesized (TiB + TiC) reinforced Ti64 composites is 1168 MPa, which is 35.5 % higher than the ultimate tensile strength of the Ti64 alloys. However, this effect resulted in a decrease in elongation at break to 2.5 %. An excellent combination of strength and fracture strain of 1060 MPa and 9.3 %, respectively, was simultaneously achieved for the heat-treated TMCs. The excellent ductility is mainly attributed to the microstructure consisting of primary equiaxed-α, ultrafine αs lamellar and retained β phase has been obtained after triple heat treatment. This finding offers significant guidance for the additive manufacturing of TMCs microstructures in order to attain the desired mechanical properties.