Gradient effects of cold rotary swaging on microstructure and mechanical properties in a Ti-12Mo-6Zr-2Fe alloy

Cold rotary-swaging was applied to the metastable β-phase Ti-12Mo-6Zr-2Fe (TMZF) alloy to achieve material with high strength parameters without compromising its low elastic modulus. The process also introduced significant location-dependent property gradient, resulting in difference in the hardness of the outer region by 28.7% compared to the interior region. The increased hardness values at the surface result from a combined contribution of dominant dislocation accumulation, enhanced crystallographic texture, and pronounced subgrain boundaries. The enhanced plastic deformation at the surface together with residual strain accumulation in the interior leads to a beneficial gradient core-shell structure, where the harder shell constrains the softer core. The interplay between the unique characteristics of the TMZF alloy and the deformation mechanisms during cold rotary-swaging demonstrates a practical pathway to tailor desirable spatially distributed mechanical properties for superior fatigue resistance in other advanced alloy systems. Specifically, this work provides quantitative microstructure distribution subjected to rotary swaging.