Hot Deformation Behavior of γ-TiAl-Based Ti–45Al–8Nb–6Cr–0.2B Alloy in the γ + β Phase Field

The hot deformation behavior of a cast Ti–45Al–8Nb–6Cr–0.2B (at.%) alloy has been investigated in the temperature and strain rate range of 1000–1200 ℃ and 0.5–0.005 s−1, respectively, using a Gleeble thermo-mechanical simulator. The as-cast pancake shows a coarse distribution of γ-TiAl laths with irregular β(B2)-phase structure (average volume fraction: γ = 0.75 and β = 0.23). Characteristics of hot deformation have been evaluated through the correlation between Arrhenius type constitutive models, processing maps, and microstructural evolution. The apparent activation energy, measured through the hyperbolic-sinusoidal relationship between flow stress, temperature, and strain rate, has been found to be 282.90 kJ/mol. The significantly low activation energy is attributed to the absence of lamellar microstructure and high volume fraction of β(B2)-phase which aids deformation at higher temperatures. Microstructural evolution of the deformed samples indicates that the flow softening corresponds to the dynamic recrystallization (DRX). DRX has been found to occur preferentially in the coarse lath boundary of the TiAl phase and also within elongated β(B2)-grains. It has been shown that extensive DRX as a result of morphological characteristics of γ-phase together with a high volume fraction of β-phase facilitates high hot workability of the present alloy.