Achieving exceptional high-temperature yield strength in TiAl alloy through microstructural optimization

Developing TiAl alloys with superior high-temperature mechanical properties remains challenging due to difficulties in integrating essential microstructural features. In this study, we introduce a novel microstructural design concept fabricated via hot extrusion at 1250°C to overcome this challenge. By incorporating features such as fine lamellar colonies, β o -strips, and nano-polysynthetic γ twin lamellae into a single microstructure (FBN microstructure), the mechanical properties are significantly enhanced. The refinement of lamellar colonies and the hindrance of crack propagation by β o -strips contribute to excellent elongation and yield strength at room temperature (RT). Furthermore, the presence of nano-polysynthetic γ twin lamellae hampers severe deformation within lamellar colonies, ensuring superior high-temperature yield strength and high ductile-to-brittle transition temperature (BDTT). Consequently, the FBN microstructure allows the TiAl alloy to achieve yield strengths exceeding 1000 MPa at both RT and 700°C, and 650 MPa at 900°C, with plastic elongation of about 1% at RT and a BDTT exceeding 900°C. These findings underscore the effectiveness of the microstructural design concept in unlocking the potential of TiAl alloys, holding significant implications for enhancing mechanical properties and opening up more possibilities for their application in high-temperature engineering.