Simultaneous enhancement of strength and ductility in a near-α Ti-3Al-2.5 V alloy via carbon microalloying

Near-α titanium alloys possess excellent cold workability, but suffer from a low strength. It is challenging to enhance their strength without the loss of ductility via conventional heat treatment or alloying method. Here, we explore the contribution of interstitial additions and precipitations in raising the strength and ductility of Ti-3Al-2.5V-xC (x = 0, 0.1, 0.2, 0.3, 0.4 wt%) near-α titanium alloys. The results demonstrate that at C contents below 0.3 wt%, carbon atoms exist as uniformly distributed interstitial solutes, significantly enhancing alloy strength through solid solution strengthening while concurrently improving ductility through three synergistic mechanisms: (1) Activation of additional pyramidal <a> and <c+a> slip systems; (2) Retention of thermally rolled α{101̅1}<1̅012> twins to coordinate plastic deformation; (3) Suppression of α{101̅2}<1̅011> twin growth during deformation, thereby sustaining grain refinement. When C content exceeds 0.3 wt%, supersaturated carbon precipitates as TiC particles, forming a “interstitial solid solution + precipitation” dual strengthening mechanism. While TiC precipitates provide strengthening equivalent to interstitial carbon, they also result in decreased ductility. Overall, the Ti-3Al-2.5V-0.3 C alloy exhibits an optimal strength-ductility synergy, achieving a tensile strength of 926 MPa and a fracture elongation of 29.5 %, corresponding to enhancements of 36 % in strength and 28 % in ductility compared to the carbon-free alloy. These findings elucidate the role of trace carbon in optimizing the strength-ductility balance in near-α titanium alloys, providing a dual-state carbon regulation strategy for designing high-strength, high-toughness, and cost-efficient titanium alloys.