Microstructural characterization of an α+β type Ti-5.5Mo-7.2Al-4.5Zr-2.6Sn-2.1Cr alloy during recrystallization annealing

An α+β 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 β phase was higher than that of the α phase, owing to the high strain energy storage of this phase during large deformation forging. Moreover, the recrystallized fraction of both the α and β phases increased with increasing holding time at 740 °C. The recrystallization fraction of the β 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 α phase dispersed in sub-structured β 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.