Tuning the strength and ductility of near β titanium alloy Ti-5321 by ω and O′ intermediate phases via low-temperature aging

The formation of intermediate phases ω and O′ during low-temperature aging at 200 °C and its effect on plastic deformation in a new-developed near β-Ti alloy Ti–5Al–3Mo–3V–2Cr–2Zr–1Nb–1Fe (wt %) have been studied in this work. The results showed that the ω and O′ phases were continuously transformed upon aging, and larger amount of O′ precipitates was developed in air-cooled sample than water-quenched one. Upon early aging the yield strength and ductility of alloy were simultaneously improved until 60 min. The trade-off relationship of strength and ductility was overcome by the simultaneous precipitation of ω and O′ phases. It was suggested that the ω and O′ precipitation changed the deformation mechanisms, leading to this alloy exhibited different deformation behaviors and mechanical properties. With the quantities of ω and O′ increasing, the strain-induced α′′ martensite transformation was gradually suppressed, and the primary deformation mechanism changed into a mixture of strain-induced ω transformation, mechanical twining and dislocation slipping. These findings would provide an insight to achieve better combinations of strength and ductility in near β-Ti alloys through tailoring the ω and O′ phase transformations.