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 rela-tionship {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 existingβ-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 transfor-mation,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.
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