Hot deformation behavior and microstructure evolution of (TiB2+TiB)/Ti-22Al-25Nb composites

Taking the (TiB2+TiB) reinforced Ti2AlNb-based composites prepared by the spark plasma sintering as the initial material, the hot compression experiments were carried out on the Gleeble − 3800 thermal simulation machine, and the hot deformation behavior of (TiB2+TiB)/Ti-22Al-25Nb composites in the temperature range of 1060 − 1150 ℃ and strain rate range of 0.05 − 5 s−1 were studied. Based on the analysis of the flow stress − strain data, the constitutive equation of the composites in the B2 single-phase region was established, and the microstructure evolution of the composites under different Zener-Hollomon(Z) parameters were analyzed. The results show that the peak stress of (TiB2+TiB)/Ti-22Al-25Nb composites decreases with the increase of deformation temperature and decrease of strain rate, and the compression curves exhibit discontinuous yielding phenomenon. The Z value plays an important role in both the microstructure evolution and deformation mechanism of the composites. When the ln Z value is at a high level, reaching 35.88, the local plastic flow deformation instability zone appeares and the dynamic recrystallization degree is low. The average dynamic recrystallized grain size is 3.82 μm and the average size of the reinforced particles is 6.93 μm. When the ln Z value is at the lower level of 29.11 − 31.28, the complete dynamic recrystallization occurs in the core region of the composites. With the decrease of Z value, the average dynamic recrystallized grain size increases to 9.16 μm when the ln Z value is 29.11. In addition, the in-situ reaction is more complete due to the accelerated diffusion of B element, resulting in the transformation of residual sintered TiB2 particles to TiBw. The average size of reinforced particles decreases to 2.77 μm. The cluster phenomenon of TiBw is significantly weakened. © 2023 Central South University of Technology. All rights reserved.