Microstructure and Superplastic Behavior of Ni-Modified Ti-Al-Mo-V Alloys

The paper studies the influence of 0.5-1.8 wt.% Ni alloying on the superplasticity, microstructural evolution, and dynamic grain growth effect in a temperature range of 625-775 degrees C and room temperature mechanical properties of two-phase Ti-Al-Mo-V alloys. Due to a decrease in beta transus and an enhancement in the alloy diffusivity, an increase in Ni content significantly improved superplasticity. The Ni-modified alloys exhibited 1.5-3-fold lower flow stress, a 2.5-3-fold greater elongation to failure, and 1.4-1.7-fold higher strain rate sensitivity m coefficient compared to the Ni-free alloy. An intermetallic Ti2Ni compound precipitated in the 1.8 wt.% Ni-modified alloy during low-temperature deformation at 700 degrees C and decreased superplastic properties. The Ti-4Al-3Mo-1V-0.1B alloy with 0.9 wt.% Ni exhibited a good combination of the superplastic behavior and room-temperature mechanical properties: an elongation to failure of 500-900% at a low-temperature range of 625-775 degrees C and constant strain rate of 1 x 10(-3) s(-1) and a yield strength of 885 MPa and ultimate tensile strength of 1020 MPa after pre-straining for 100% in a superplastic regime and strengthening heat treatment.