Effect of hot rolling and primary annealing on the microstructure and texture of a β-stabilised γ-TiAl based alloy

Titanium aluminide alloys based on the ordered gamma-TiAl phase are intermetallic materials well suited for lightweight high-temperature applications. The TNM alloys, a specific, beta-solidifying group among them with.a nominal composition of Ti-43.5Al-4Nb-lMo-0.1B (at.-%), offer a homogeneous and fine-grained microstructure upon casting. This advantage has been exploited to develop a lab -scale hot rolling process in which a cost-effective ingot breakdown of the starting material is omitted. The present work establishes a fundamental understanding of the processes prevailing in the material during hot rolling and primary annealing. Microstructural analysis and texture measurements conducted at a synchrotron radiation source allow to study deformation, recovery, recrystallisation, as well as phase transformation mechanisms in detail. Different hot rolling procedures conducted within the (alpha+beta) and (alpha -beta/beta(o)-1-gamma) regions of the phase diagram are considered and investigated with regard to the prevalent mechanisms. Hot rolling in the (alpha+beta) region entails an alpha(2) phase texture novel in gamma-TiAl based alloys. Hot rolling in the (alpha+beta/beta(o)+gamma) region near the gamma-solvus temperature particularly promotes the breakdown of the initial microstructure in TNM alloys. A specially designed hot rolling process prevents the accumulation of a modified cube texture component in the gamma-TiAl phase that is typically linked to anisotropic mechanical properties.(C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.