Mechanism of abnormal rolling microstructure in Ti₂AlNb alloy hot-rolled plate

This paper analyzes the anomalous orientation delamination state exhibitedby the microstructure of Ti₂AlNb hot-rolled plates after heat treatment. The microstructure of samples in both hot-rolled and heat-treated conditions was analyzed using Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD). The hot-rolled plates exhibited a near-equiaxed microstructure similar to recrystallization. Moreover,the proportion of the low-temperature equilibrium phase O-phase exceeded 60%. In the hot-rolled state,the majority of the β-phase and O-phase aligned with the orientation relationship 110_β//001_O,< 111> _β//< 1-10> _O. Subsequent high-temperature heat treatment led to the transformation of O-phase to the β-phase,while fast cooling retained the β-phase,resulting in noticeable orientation delamination. The texture type of the β-phase exhibited minimal change before and after heat treatment,indicating that the formation of the high-temperature β-phase involves existing β-phase grains from the hot-rolled state growing by engulfing surrounding O-phase grains at elevated temperatures. Consequently,the orientation distribution state of the β-phase is kept after phase transformation,leading to a distinctive orientation layer state. The equiaxed microstructure in hot-rolled sheets arises from the high-temperature β-phase transition,and the strong texture of the low-temperature O-phase is inherited from the strong texture of the high-temperature β-phase. These result provide a foundation for our understanding of the Ti₂AlNb hot-rolled microstructure and insights for microstructure regulation.