Enhanced microstructural homogeneity and strength-ductility synergy of Ti-6Cr-5Mo-5V-4Al β-titanium alloy wires through boron addition

One of the long-term concerns regarding titanium alloy wires involves microstructural inhomogeneity, mechanical instability and product unreliability in service. In this study, a strategy of micro-alloying was utilized to address the issue in Ti-6Cr-5Mo-5V-4Al (Ti6554) β-titanium alloy wires. The microstructures and mechanical properties of Ti6554 hot-rolled wires were optimized through boron (B) additions. The results manifest that B-addition promotes microstructural homogenization of wires, wherein the microstructure nearly completely consists of normal grain region (NGR) without abnormal grain region (AGR) like that in the B-free alloys. This microstructural homogenization relieves mechanical fluctuation amongst different samples and renders plastic flow highly repeatable upon stretching. Meanwhile, B-addition strengthens wires whilst maintains decent ductility and thereby achieves the better combination of strength and ductility in comparison with that in the B-free wires. The analyses indicate that the addition of B facilitates the universal occurrence of dynamic recrystallization (DRX) to form NGRs at the expense of AGRs, which is beneficial to microstructural homogenization of hot-rolled wires. A good plastic accommodation resulting from NGRs and strengthening caused by TiB laths endow Ti6554 wires superior strength-ductility synergy. These findings provide helpful guidance for microstructural and performance optimization of titanium alloy wires.