Needle-like morphology in a high-(Nb,Al)-contained TiAl-based alloy produced under 800 °C plus compression

In this paper, γ' (γ variant) in TiAl-based alloy is newly discovered. The high-(Nb,Al)-contained Ti-47Al-8Nb model alloy is used. The alloy is firstly held at 1300 °C for 60 min following by water quenching. Then it is held at 800 °C for different time without/with compression stress following by water quenching again. Results show that, with a 300 MPa initial compression stress, the fine needle-like morphology can be discovered in block γ phase. The needle-like morphology contains two kinds of γ variants. One is the well-known γ_T twin, i.e., Σ3 twin. The other is the newfound γ', whose c-axis has turned to its initial a-axis or b-axis directions, and a-axis or b-axis maintains the initial direction.