Effect of Mo content on the microstructure, superplastic behavior, and mechanical properties of Ni and Fe-modified titanium alloys.

Novel titanium-based alloys are required to increase the efficiency of superplastic forming technology and decrease energy consumption. For this purpose, the superplastic deformation behavior, strain-induced microstructure evolution in a temperature range of 625–775 °C, and post-deformation mechanical properties of Ti–4Al–1V–1Fe–1Ni-0.1B- x Mo alloys (x = 1, 2.5, or 5 wt%) were investigated. The studied alloys demonstrated a stable flow with a high strain rate sensitivity coefficient m of 0.50–0.65 and an elongation-to-failure δ of 700–1000% at temperatures of 700–775 °C. Molybdenum insignificantly influenced superplastic deformation behavior at high temperatures due to a high fraction of the β phase of 22–62%. The Mo effect was significant at a low deformation temperature of 625 °C. At this temperature, an increase in Mo content from 1 to 5% provided the β -phase fraction above the critical value of ∼20% and increased the m- value from 0.4 to 0.5 and δ from ∼200 to ∼700%. Increasing Mo from 1 to 5% enhanced the post-deformation yield strength at room temperature by 180 MPa, the ultimate tensile strength by 170 MPa, and the ductility by 2.5%. Consequently, alloying Ti–4Al–1V–1Fe–1Ni-0.1B with 5% Mo provided an excellent combination of superplasticity at a low temperature of 625 °C and post-forming tensile mechanical properties. • Increase in Mo content from 1 to 5 wt% improved low temperature superplasticity. • 5Mo and 20% of the β phase are required for low-temperature superplasticity at 625 °C. • Alloys exhibit a stable fine-grained structure during deformation at 625–700 °C. • Increase in Mo content improved the post-forming mechanical properties. • 5 wt%Mo provided a good combination of the superplastic and mechanical properties. [ABSTRACT FROM AUTHOR]