Variation in the major axes of TiB ₂ in TiAl alloy induced by changes in supersaturation of boron

Abstract Borides play a direct role in determining the mechanical properties of boron‐containing TiAl alloy castings. Studying the growth habits of borides is crucial for controlling their morphology and size. In this study, SEM and HRTEM techniques were employed to characterize TiB 2 particles in Ti‐45Al‐2Mn‐2Nb‐1.25B alloy. TiB 2 particles in the alloys mainly exhibit blocky, needle‐like, ribbon‐like and sixfold symmetrical morphologies. Atomic‐scale characterization revealed that blocky and ribbon‐like TiB 2 particles exhibit different major axes, [0001] and [], respectively. A novel sixfold symmetrical TiB 2 particle was observed, formed by the combination of these two particle types. The change in B atom supersaturation during the solidification process was found to be the primary factor influencing the major axes of TiB 2 particles. During the early stages of solidification, the high supersaturation of B atoms in the melt led to equilibrium conditions. TiB 2 particles grew predominantly in a blocky shape with [0001] as the major axis. As the supersaturation of B atoms decreased, the scarcity of B atoms caused crystal growth to deviate from equilibrium, the () plane exhibited the fastest growth rate due to its requirement for the shortest range of atomic rearrangement and highest attachment energy, TiB 2 particles assumed a ribbon‐like shape. Consequently, the growth of TiB 2 particles underwent a transition between these two growth mechanisms, forming a sixfold symmetrical morphology. This finding helps understand the growth behavior of precipitates in TiAl alloy solidification, enabling control of boride morphology and improving alloy performance, thus providing theoretical insights into strengthening phase formation in metals.