Effect of inter-pass annealing on the deformation microstructure of Ti-48Al-2Cr-2Nb alloy

Abstract

TiAl alloy is a potential candidate structural material for lightweight and high temperature in aerospace, and multi-pass thermo-mechanical treatment, where dynamic recrystallization (DRX), static recrystallization (SRX), and post-dynamic recrystallization (PDRX) have significant effects on microstructure evolution, is commonly applied for microstructure control due to its poor plasticity. Accordingly, the complex recrystallization behaviors of Ti-48Al-2Cr-2Nb alloy were investigated by hot simulation compression experiments. The results of metallographic statistics showed that microstructure inhomogeneity of uniaxial compression could not be improved by changing the temperature and strain rate to adjust the DRX degree. Additionally, discontinuous dynamic recrystallization (DDRX) characterized by the formation of twining boundaries was a dominant DRX mechanism and generated at grain boundaries. Meanwhile, continuous dynamic recrystallization (CDRX) was formed within the grains and at grain boundaries, accompanied by the relatively high distortion at the initial stage. Residual deformed microstructure owing to the incomplete DRX could be eliminated by SRX and PDRX during the inter-pass annealing. A method based on the grain size difference induced by various recrystallization mechanisms was proposed to reveal that grain growth resulting from PDRX played a primary role and SRX was impaired with the increasing strain. The interaction effect of DRX, SRX, and PDRX during the multi-pass deformation could achieve the uniform microstructure, which is consistent with a near-isothermal multi-pass multidirectional canned forging process designed in the paper. Eventually, room-temperature tensile tests demonstrated that the mechanical properties of wrought billet were distinctly enhanced.