Superplastic deformation behaviors of fine-grained Ti-15 V-3Cr-3Al-3Sn alloy prepared via ultra-low heat input friction stir processing

Abstract

In this work, a fine-grained Ti-15 V-3Cr-3Al-3Sn alloy with 0.93 μm in average grain size and 75.6% of high-angle grain boundaries was achieved by ultra-low heat input friction stir processing (FSP). The superplastic behavior of the friction stir processed (FSPed) sample was investigated at the temperature of 600 °C–700 °C and strain rates range of 1 × 10−4 s−1-3 × 10−3 s−1. The FSPed sample exhibited the largest elongation of 1110% at 675 °C and 3 × 10−4 s−1. This elongation was the largest reported for the alloy to date. The main reasons could be drawn as follows: Firstly, the α phase precipitated during the heating process before superplastic deformation pinned the β grain boundaries in the subsequent superplastic deformation process. Secondly, the dynamic recrystallization occurred during superplastic deformation, which significantly refined the grains and kept the ratio of high-angle grain boundaries >80%. Thirdly, an obvious diffusional creep of the β grains was observed in the late superplastic deformation period, which coordinated the sliding of β grain boundaries. In summary, the superplastic deformation mechanism of the FSPed sample deformed at 675 °C and 3 × 10−4 s−1 was grain boundary sliding accompanied by dynamic recrystallization and diffusional creep.