Deformation and phase transformation behaviors of a high Nb-containing TiAl alloy compressed at intermediate temperatures

In modern β-solidified TiAl alloys, the decomposition of α$_2$ phase is frequently observed during heat treatment or high-temperature deformation of the alloys. In this study, high-temperature deformation and decomposition mechanisms of α$_2$ phase in a Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y alloy are investigated. In a sample deformed at 800 °C, the precipitation of β$_o$(ω$_o$) phase is observed within the equiaxed α$_2$ phase. The nucleation of ω$_o$ particles within the β$_o$ matrix indicates the α$_2$ → β$_o$ → ω$_o$ transformation. In addition, numerous γ phase precipitates form within the β$_o$(ω) areas. The α$_2$ lamellae decompose into ultrafine (α$_2$+γ) lamellae and coarsened γ lamellae via α$_2$ → α$_2$ + γ and α$_2$ → γ transformation, respectively. Moreover, the ω$_o$ phase nucleates within the ultrafine lamellae via α$_2$ → ω$_o$ transformation. However, in a sample deformed at 1000 °C, the nucleation of β$_o$ particles is sluggish, which is caused by the efficient release of the internal stress via dynamic recrystallization (DRX). These results indicate that complex phase transformations can be introduced by the decomposition of α$_2$ phase in TiAl alloys with a high amount of β-stabilizing elements