Effect of yttrium and erbium on the microstructure and superplasticity of Ti–4Al–3Mo–1V alloy

Abstract

The influence of small Y and Er additions (0.2 wt.%) on the supraplastic behavior and microstructural evolution of Ti–Al–Mo–V alloys during thermomechanical processing and superplastic deformation was investigated. Alloying with 0.2% Y can effectively modify the cast structure, decreasing the mean grain size from 670 to 225 μm, while addition of 0.2% Er exhibited no modifying effect. Thermomechanical processing promoted the refinement of oxide particles, resulting in compact particles measuring ≈0.2 μm for the Er-bearing alloy and ≈0.1 μm for the Y‑bearing alloy. The alloys with Y and Er additions and the base alloy without additives exhibited close superplastic characteristics at temperatures of 775 and 875 °C, strain-rate sensitivity coefficient m = 0.45–0.55, and elongation ≈400–800% at strain rates of 1·10⁻³ and 2·10⁻⁴ s⁻¹. Alloying with Y and Er reduced the flow stress during superplastic deformation, which is attributed to the acceleration of recrystallization and globularization of the microstructure due to oxide particles. Also, the inhibiting effect of Y oxide particles on grain size during annealing in the single-phase β-region and during superplastic deformation at low strain rates was revealed, while no effect was observed in the alloy with Er.