The influence of rolling temperature on texture evolution and variant selection during α — β —α phase transformation in Ti-6Al-4V

摘要

The role of starting texture in variant selection has been studied during α —> β —α transformation in Ti-6Al-4V. By hot rolling at different temperatures followed by recrystallization, material with either a strong basal texture or a strong transverse texture was generated. Subsequently, both conditions were heat-treated above the β transus followed by slow cooling. The degree of variant selection was assessed by comparing the strength of the measured and predicted α texture from high temperature β texture, assuming equal occurrence of all possible variants during β —α transformation. It was found that, even though the material rolled originally at 800 °C displayed a stronger a texture after β heat treatment, it was the material rolled originally at 950 °C that showed greater variant selection. The variant selection mechanism is discussed in terms of the generated β texture and common (110) poles in neighbouring β grains selecting a similar α variant on both sides of the prior β grain boundary. Predictions of possible (110) pole misorientation distributions for the two investigated β textures showed that the combination of texture components generated during rolling Ti--6Al-4V at 950 °C increases the likelihood of having β grain pairs with closely aligned (110) planes compared to rolling at 800 °C. Therefore, it can be proposed that avoiding the generation of certain combinations of β texture components during thermomechanical processing has the potential for reducing variant selection during subsequent β heat treatment.