Fabrication and Characterization of In Situ Ti-6Al-4V/TiB Composites by the Hot-Pressing Method using Recycled Metal Chips

In this study, a Ti-6Al-4V matrix composite reinforced with in situ synthesized TiB whiskers has been successfully produced from wasted chips by a cost-effective powder metallurgy route combining rapid heating and hot pressing. The effect of boron powder addition (1 vol.%, 3 vol.%, 5 vol.%, and 7 vol.%) on phase constituents, microstructures, and mechanical properties of the fabricated composites was investigated. Additionally, the effect of two different post-heat treatments on the 3 vol.% boron-containing composites was also explored. The results show that the ultimate tensile strength (UTS) and yield strength (YS) of the composite first increase when the content of boron is less than 3 vol.%, and then start to decrease with the further increase of boron content. The TiB reinforcement layers change from discontinuous to quasi-continuous and then to continuous with increasing boron content, which is attributed to a higher fraction of agglomerated TiB reinforcement phases. The composites with 1 vol.% (UTS of 1085 MPa, strain to fracture of 5.83%) and 3 vol.% (UTS of 1127 MPa, strain to fracture of 3.98%) boron powder addition show optimized tensile properties. The mechanical properties of 3 vol.% boron-containing composites are not significantly improved after heat treatment. Our experimental results demonstrate the feasibility of fabricating low-cost, high-performance titanium alloy matrix composites from Ti-6Al-4V machining chips. It can serve as a promising and cost-effective method to directly utilize Ti-6Al-4V chips to fabricate strong and ductile Ti-6Al-4V composites for niche applications.