Transitional structure of {332}< 113 > beta twin boundary in a deformed metastable beta-type Ti-Nb-based alloy, revealed by atomic resolution electron microscopy

In this work, the boundary structure of the (332)< 113 >(beta) deformation twin in a deformed metastable beta-type Ti-Nb-Pd alloy has been clearly revealed by means of high-angle annular dark-field scanning transmission electron microscopy at atomic-resolution level. It is found that stress-induced alpha martensite structure remains in the {332}(beta) twin boundary region, exhibiting a gradual transition to the 13 structure with an orientation relationship of (1(3)over-bar0)(alpha)//(332)(beta). This finding provides a direct experimental evidence to verify that the formation of a (334 twin in deformed metastable (beta-type Ti-Nb-based alloys can be associated with a reversible beta-to-alpha martensitic transformation. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.