Heterostructures enhance simultaneously strength and ductility of a commercial titanium alloy

Abstract

Enhancing both strength and ductility simultaneously in commercial alloys at an industrial scale remains a challenging task. In this study, we have demonstrated a simple heat treatment method to achieve a heterostructure with coarse and ultra-fine lamellar α precipitates in a common titanium alloy, Ti-5Al-5Mo-5V-3Cr-1Zr. Guided by computer simulations, we successfully attained microscale concentration modulations in the β-phase matrix using up-quenching of a duplex microstructure consisting of a globular primary α phase (αp) and β matrix to dissolve the αp phase rapidly and leave residual concentrations. We subsequently applied aging treatments to create finely dispersed regions of coarse and ultra-fine α precipitates embedded in the β matrix by activating different phase transformation mechanisms. Compared to the commercial alloy that has a homogeneous lamellar structure, the heterostructured alloy we produced exhibits a 6% increase in ultimate tensile strength and a remarkable 130% increase in elongation. The outstanding ductility of the heterostructured alloy is attributable to its unique microstructure design, which prevents strain localization and allows full activation of dislocation and twin deformations in the coarse and ultra-fine α regions. Meanwhile, the high strength of the alloy can be attributed to the enhanced back stress effect induced by strain partitioning of the heterostructure. Our study demonstrates a simple and effective method for creating bulk heterostructures in precipitation-hardened alloys at an industrial scale, leading to substantially improved strength and ductility.