Microstructural characterization of an alpha plus beta type Ti-5.5Mo-7.2Al-4.5Zr2.6Sn-2.1Cr alloy during recrystallization annealing

摘要

An alpha+beta type titanium alloy was subjected to various periods of recrystallization annealing and the resulting microstructural evolution was characterized. The results revealed that the recrystallization rate of the beta phase was higher than that of the a phase, owing to the high strain energy storage of this phase during large deformation forging. Moreover, the recrystallized fraction of both the alpha and beta phases increased with increasing holding time at 740 degrees C. The recrystallization fraction of the b phase accounted for 70.13% after annealing for 5 h. However, the average grain size remained constant when the recrystallization fraction reached approximately 54%, indicating that further grain refinement was prevented, owing to the high degree of recrystallization. The spatial microstructure which consisted of a globular, homogeneous, and equiaxed alpha phase dispersed in sub-structured beta matrix grains, was characterized via a novel three-dimensional electron backscatter diffraction technique. The grain orientation and morphological parameters, including the equivalent-sphere diameter and number of neighboring grains, were calculated and discussed. (C) 2017 Elsevier B.V. All rights reserved.