Investigation on the mechanism of improving the compressive creep properties of TiAl alloys by heat treatment: The strengthening effect of carbides

Abstract

In order to develop high-performance TiAl alloys, Ti-43Al-6Nb-1Mo-1Cr-0.5C-0.05Y₂O₃ alloy was prepared in the study, and the alloy then was heat treated. The high-temperature compression creep tests of alloys before and after heat treatment were performed. By analyzing the microstructure before and after heat treatment and compression creep, the influence mechanism of heat treatment on creep performance of alloys was revealed. The results indicate that heat treatment can efficiently enhance the compressive creep performance of alloys. The mechanism of heat treatment improving the creep resistance of alloys is mainly the strengthening effect of carbides (Ti₂AlC). Besides, the precipitation mechanism of carbides is elucidated, which is significantly different from the mechanism of conventional lamellar degradation to form carbides. The carbides in the lamellae can inhibit the lamellar decomposition, which causes the improvement of creep performance. The obvious microstructural evolution occurs during compression creep, mainly including dynamic recrystallization, lamellar degradation, B2→γ and the precipitation of Ti₂Al phases. Continuous dynamic recrystallization, discontinuous dynamic recrystallization and twin-induced dynamic recrystallization all appear during creep, and discontinuous dynamic recrystallization is the main recrystallization mechanism. The degradation of lamellae leads to the interruption of α₂ lamellae and the precipitation of B2 phases. The B2→γ reaction induces the formation of layered B2/γ structure. Finally, the reason why the Ti₂Al phases appear in the blocky B2 phases is clarified.