Tailoring microstructure and mechanical performance of a β-solidifying TiAl alloy via martensitic transformation

This study aimed to tailor the microstructure and mechanical properties of a beta-solidifying TiAl alloy via martensitic transformation. The as-cast microstructure of the applied alloy, Ti-42Al-8.5V (at. %), was characterized by large Widmanstatten colonies, forming the so-called micro-textured morphology. After oil quenching from beta phase field, martensitic transformation occurred so that most of the prior beta phase was transformed into fine martensitic laths with various orientations. Although variant selection was noted in local regions, the micro-texture was evidently mitigated in comparison with the initial state. During the subsequent tempering processes, the martensite decomposed via alpha(2) -> alpha(2) + gamma -> beta(0) + gamma, whereby two different microstructures were obtained. At lower tempering temperatures (<800 degrees C), the microstructure was mainly comprised of multi-orientated alpha(2)/gamma lamellar structure with ultra-fine lamellar spacing. Meanwhile, a near-equiaxed (beta(0) + gamma) structure was produced at higher tempering temperatures (> 900 degrees C), which was characterized by ultra-fine gamma platelets embedded in the beta(0) matrix. Hot tensile tests revealed that the two microstructures had distinct mechanical properties. The former exhibited quite high strength at elevated temperatures and hence might be a candidate for high temperature service, while the latter was much softer and more suitable for thermomechanical processing.

Automated summary

This study achieved microstructure and mechanical properties adjustment of a beta-solidifying TiAl alloy through martensitic transformation, resulting in two different microstructures with distinct mechanical properties, suitable for high temperature service and thermomechanical processing, respectively.