Formation of core-shell-like structure in β-solidified TiAl alloy and its effect on hot workability

Understanding how phase evolves from its parent phase is critical to control the transforming microstructures and thus material performance. TiAl alloys exhibit lightweight and excellent elevated temperature properties, making them suitable for high-temperature applications. However, it is difficult to further improve the microstructure and properties of TiAl alloys through hot working, as the lamellar colonies in the original microstructure cannot be completely broken up. These remnant colonies are hard to eliminate and their presence reduces the microstructural homogeneity and properties of the alloys. Here, we propose a method for complete fragmentation of the lamellar structure in the β-solidified TiAl alloys by introducing a core-shell-like structure before hot working. The core-shell-like structure with a (α₂+γ) lamellar colony in the core and an α₂ matrix in the shell is obtained. The lamellar decomposition dominated by non-classical L1₀ (γ) to hcp (α) phase transformation is essential to ensure the formation of the core-shell-like structure, while the effects of factors such as defects and β₀ grains are also further discussed in the thesis. In addition, the core-shell-like structure obtained in the β-solidified TiAl alloys before hot working can enhance the hot workability.