Responses of microstructure and texture of α phase to boron addition in Ti-40Al-8Nb-xB alloys modified by hot deformation above the β transus

Abstract

In this study, hot deformation is performed in the β-phase region in Ti-40Al-8Nb-(0, 0.5, 1)B alloys (at. %) in order to modify the microstructures of the β phase and borides in the alloys. Special attention is paid to the effect of boron content on the microstructure of the transformed α phase. The obtained results show that the microstructure of the α phase is significantly different in compressed samples with different boron contents. The α phase has a lath-like morphology in the Ti-40Al-8Nb alloy, whereas it has equiaxed features in the boron-added alloys. The morphology of the α phase is closely related to whether the α phase follows the Burgers orientation relationships (BORs) with the β matrix, i.e., lath-like morphologies of the α phase when it follows the BORs and equiaxed morphologies when it does not follow the BORs. In addition, in the compressed samples of the Ti-40Al-8Nb, Ti-40Al-8Nb-0.5B, and Ti-40Al-8Nb-1B alloys, the α phase has an 〈11−20〉 fiber texture, an 〈11–20〉–〈10–10〉 double fiber texture, and randomly crystallographic orientations, respectively. Detailed analyses demonstrate that the intensity of the 〈11–20〉 fiber texture of the α phase is governed by a combination of the volume fraction of the α phase that has BORs with the β matrix and the intensity of the 〈111〉 fiber texture of the β phase, whereas the intensity of the 〈10−10〉 fiber texture of the α phase is affected by the reorientation behavior of borides during the deformation.