Drastic enhancement in hot-workability and microstructural refinement of TiAl alloys via martensitic transformation: A comparative study

In this study, the hot deformation behavior of a Ti–42Al-8.5 V alloy with a martensitic staring microstructure was investigated for the first time. For comparison, the same alloy but with a Widmannstatten lamellar structure was also prepared and deformed at identical conditions. It was shown that the martensite exhibited a much lower stress exponent and pronounced flow softening, and the hot-workability was drastically improved. With the aid of the rapid decomposition of the martensite, an excellent fine-grained structure with negligible micro-texture was obtained in a wide temperature-strain rate regime, which was mostly surrounded by high-angle grain boundaries through recrystallization/globularization enhanced by grain boundary sliding. In contrast, the Widmannstatten structure showed a rather poor hot-workability and a retarded refinement efficiency. The deformed microstructure was noticeably non-uniform and micro-textured at nearly all the compression conditions, though the recrystallized grain size was comparable with that of the martensite. To rationalize the distinct deformation behavior of the two starting microstructures, the underlying mechanisms governing the microstructure/orientation evolution were systematically analyzed and discussed. It was suggested that adopting martensite as the starting microstructure may be a potential approach to achieve the optimal microstructural breakdown effect for certain TiAl alloys.