Hot deformation behavior and dynamic recrystallization of a β-solidifying TiAl alloy

Abstract

Hot deformation behavior and dynamic recrystallization (DRX) of a β-solidifying TiAl alloy Ti–43Al–2Cr–2Mn–0.2Y (at%) were investigated by means of isothermal compression tests in a temperature range of 1100–1225°C and strain rate range of 0.01–0.05s−1. A processing map at a true strain 0.8 was developed based on the dynamic materials model. The current alloy possesses a wide processing window, and the optimum deformation condition is 1175–1225°C/0.05s−1. The main softening mechanism is DRX of γ grains. The DRX proceeded preferentially at triangle boundaries, and subsequently in the lamellae. Both deformation temperature and strain rate have an obvious impact on the microstructural evolution. The partial DRX occurred when the alloy deformed at low temperature and high strain rate. Some remnant lamellar structures existed due to the plastic anisotropy of lamellar colony. With the increase of temperature and /or the decrease of strain rate, the lamellae were effectively broken down into fine grains, and a relatively complete DRX occurred. Dynamic recovery is the main deformation mechanism for β0 phase, which promotes the compatible deformation between γ and α2 phases and prevents premature cracks. Additionally, the DRX mechanism of γ phase was investigated through TEM observations. The DRX of γ grains begins with the formation of sub-boundaries, followed by a process of rearrangement of sub-boundaries to form new grains.