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 β-solidifying TiAl alloy via martensitic transformation. The as-cast microstructure of the applied alloy, Ti-42Al-8.5V (at. %), was characterized by large Widmanstätten colonies, forming the so-called “micro-textured” morphology. After oil-quenching from β phase field, martensitic transformation occurred so that most of the prior β 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 α₂′ → α₂ + γ → β₀ + γ, whereby two different microstructures were obtained. At lower tempering temperatures (<800 °C), the microstructure was mainly comprised of multi-orientated α₂/γ lamellar structure with ultra-fine lamellar spacing. Meanwhile, a near-equiaxed (β₀ + γ) structure was produced at higher tempering temperatures (>900 °C), which was characterized by ultra-fine γ platelets embedded in the β₀ 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 thermo-mechanical processing.