Achieving superior strength-ductility synergy in near-α Ti–6Al–3Nb–2Zr–1Mo alloy via hot isostatic pressing and solution-aging treatments

The near-α Ti-6Al-3Nb-2Zr-1Mo (Ti-6321) titanium alloy is widely used in marine engineering, however, its relatively low strength-ductility matching limited the application in harsher deep-sea environments. This study proposes a novel approach through hot isostatic pressing (HIP) combined with solution-aging treatments (STA) using large-diameter spherical powders (∼127 μm), achieving superior strength-ductility synergy in Ti-6321 alloy. Microstructure evolution, precipitate characteristics and mechanical properties of the alloys under different sintering temperatures and STA parameters were systematically investigated. Results indicated that the alloys were HIPed at 940 °C/120 MPa for 3h, exhibiting moderate tensile strength (ultimate tensile strength (UTS): 876±16 MPa; yield strength (YS): 798±15 MPa) and excellent elongation (EL): 18.3±0.6 %. After further 965 °C/ST(WQ)+600 °C/AG(AC), alloys achieved a superior combination of strength and ductility (UTS: 1064±17 MPa, YS: 963±23 MPa, EL: 15.8±0.8 %), outperforming most conventionally processed and post-treated Ti-6321 alloys. Fundamentally, the excellent mechanical properties of as-HIPed alloys are attributed to the combination of equiaxed α p grains plus lath-like structure and relatively fine grain size. After STA treatments, the alloys exhibit a trimodal microstructure consisting of equiaxed α (α p ), lamellar α (α l ), and β t (β matrix precipitated with secondary α s ). The high tensile strength mainly stems from α s precipitation strengthening. Meanwhile, the hierarchical distribution of α p and α l in the β t matrix facilitates strain coordination, thereby ensuring great ductility. This work provides valuable insights into the cost-effective fabrication of Ti-6321 alloy with exceptional mechanical properties, supporting its sustainable application in harsh deep-sea environments.