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

The role of starting texture in variant selection has been studied during alpha -> beta -> alpha 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 beta transus followed by slow cooling. The degree of variant selection was assessed by comparing the strength of the measured and predicted alpha texture from high temperature beta texture, assuming equal occurrence of all possible variants during beta -> alpha transformation. It was found that, even though the material rolled originally at 800 degrees C displayed a stronger alpha texture after beta heat treatment, it was the material rolled originally at 950 degrees C that showed greater variant selection. The variant selection mechanism is discussed in terms of the generated beta texture and common < 1 1 0 > poles in neighbouring beta grains selecting a similar alpha variant on both sides of the prior beta grain boundary. Predictions of possible < 1 1 0 > pole misorientation distributions for the two investigated beta textures showed that the combination of texture components generated during rolling Ti-6Al-4V at 950 degrees C increases the likelihood of having beta grain pairs with closely aligned (1 1 0) planes compared to rolling at 800 degrees C. Therefore, it can be proposed that avoiding the generation of certain combinations of beta texture components during thermomechanical processing has the potential for reducing variant selection during subsequent beta heat treatment. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.