A strengthening strategy for metastable β titanium alloys: Synergy effect of primary α phase and β phase stability

Increasing strength and preserving high strain hardening rate are of importance to widen the application of the metastable beta titanium alloys. In this study, Ti-4Mo-4Cr-3Al-2Nb-1.2V-1Zr-1Sn (wt.%) alloy with four different primary alpha phase contents were prepared by solution treatment at different temperatures. The differences in beta phase stability, mechanical properties, and deformation modes in these samples were investigated systemati-cally. With the decrease of solution treatment temperature, the volume fraction of alpha phase, the stability of beta matrix, and the tensile strength of the alloy increase, and a high strength and high strain hardening rate can be achieved simultaneously when the content of the primary alpha phase is less than 20%. When the applied stress exceeds the activated stress of martensitic transformation, martensite plates can be generated at large beta domains and caused a dynamic Hall-Petch effect in these samples. With the further increase of strain, substructures are generated within the martensite to accommodate the deformation. Our findings provide a possible route for strengthening the metastable beta titanium alloys and are beneficial to the microstructure design of the alloys with a high strength-ductility combination.