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 β titanium alloys. In this study, Ti–4Mo–4Cr–3Al–2Nb–1.2V–1Zr–1Sn (wt.%) alloy with four different primary α phase contents were prepared by solution treatment at different temperatures. The differences in β phase stability, mechanical properties, and deformation modes in these samples were investigated systematically. With the decrease of solution treatment temperature, the volume fraction of α phase, the stability of β 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 α phase is less than 20%. When the applied stress exceeds the activated stress of martensitic transformation, martensite plates can be generated at large β 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 β titanium alloys and are beneficial to the microstructure design of the alloys with a high strength-ductility combination. • The strengthening strategy of changing the content of primary α phase was applied to a new metastable β titanium alloy. • The roles of primary α phase in deformation process and martensite transformation were evaluated. • The deformation mechanism of Ti-4321 alloy as a function of phase stability and deformation strain was proposed.