β-phase stability-controlled deformation behavior and mechanical performance in metastable Ti–Cr alloys

초록

The relationship between β-phase stability, deformation behavior, and mechanical properties was systematically investigated in metastable β Ti–Cr alloys containing 7–12 wt% Cr. Increasing Cr content progressively stabilized the β phase through suppression of the metastable ω phase and reduction of the β-phase lattice parameter from 3.2578 Å to 3.2430 Å. The Ti–8Cr alloy exhibited the most favorable strength–ductility balance, achieving a yield strength of 763 MPa, an ultimate tensile strength of 1033 MPa, and an elongation of 48%. EBSD analysis revealed extensive {332}< 113 > deformation twinning with a twin fraction of 21.8%, resulting in sustained strain hardening and enhanced tensile ductility. In contrast, increasing β-phase stability progressively suppressed deformation twinning, reducing the twin fraction to 3.9% in Ti–10Cr and to a negligible level in Ti–12Cr. Consequently, higher β-phase stability reduced deformation-twin activity and shifted the dominant deformation behavior from TWIP-dominated deformation toward slip-dominated deformation through an intermediate twinning–slip transition regime. Based on the combined crystallographic, mechanical, post-deformation microstructural, and fracture analyses, a β-phase-stability-dependent correlation map was established to quantitatively describe the relationships among β-phase stability, the XRD-detectable ω response, deformation-twin activity, work-hardening behavior, and tensile performance. The results demonstrate that an appropriate level of β-phase stability provides the most favorable balance among reduced XRD-detectable ω content, deformation-twin activity, sustained work hardening, and tensile ductility, providing practical guidelines for β-phase stability engineering in metastable β titanium alloys.

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