Microstructure Evolution and Mechanical Response of Ti-(43-45)Al-4Nb-1Mo-0.2B Alloys During the Hot-Pack Rolling

Slight variations in the Al content can considerably affect the solidification path of TiAl alloys. Consequently, these variations influence the location of phase regions during the hot deformation process of TiAl alloys. In this study, Ti-(43-45)Al-4Nb-1Mo-0.2B (TNM, atomic fraction, %) ingots were synthesized via arc melting and labeled as 43Al, 44Al, or 45Al depending on their Al contents. Subsequently, TNM sheets were fabricated via hot-pack rolling, and the influence of Al content on the microstructure evolution and mechanical properties of these sheets during the rolling process was systematically investigated.Results indicate that TNM alloys with different Al contents are located in different phase regions when deformed at 1250^oC. After preheating for 1 h, the 43Al alloy is mainly composed of equiaxed α/α₂ grains. In contrast, the 44Al alloy exhibits a unique core-shell-like structure with α₂/γ lamellar colonies in the core and α/α₂ grains surrounding it. Compared with the 44Al alloy, the 45Al alloy demonstrates a lamellar structure with larger α₂/γ lamellar colonies. Furthermore, the initial structure remarkably influences the microstructure evolution of TNM sheets during the rolling process and determines the final microstructure composition of these sheets. With increasing Al content, the microstructure of TNM sheets transitions from nearly lamellar to duplex, eventually tending toward a near-γ structure. Additionally, two types of α₂/γ lamellar colonies—newly formed and initially present—are observed in the 43Al and 45Al sheets, respectively. Owing to its unique core-shell-like structure, the 44Al sheet simultaneously contains both types of α₂/γ lamellar colonies. Furthermore, the mechanical properties of TNM sheets with different Al contents were tested at room temperature. Results show a gradual decrease in the tensile strength of TNM sheets with increasing Al content. The 43Al sheet exhibits the best performance, which is attributed to the presence of newly formed lamellar structures. Meanwhile, the 44Al and 45Al sheets develop fractures rapidly because of the increased, clustered, and abnormal growth of equiaxed γ grains or presence of residual α₂/γ lamellar colonies.