Enhanced creep properties and creep-induced microstructure evolution behavior of carbon-doped TiAl alloys

Abstract

In this paper, the tensile creep experiments at 750–850 °C under 150 MPa were conducted on Ti-43Al-6Nb-1Mo-1Cr (at.%) alloy and Ti-43Al-6Nb-1Mo-1Cr-0.5C alloy. The findings reveal that the high-temperature creep performance of both alloys exhibits significant sensitivity to the creep temperature. Introducing the C element leads to a significant reduction in the steady-state creep rate and enhances the creep performance of TiAl alloys. Furthermore, the creep apparent activation energy increases from 334.52 kJ mol⁻¹ to 350.85 kJ mol⁻¹ following the introduction of C. Microstructure evolution during creep encompasses several typical types: (i) dynamic recrystallization, which predominantly occurs at the lamellar colony boundaries and has a softening effect; (ii) phase transformation from the B2 phase to the γ phase, leading to the formation of ellipsoidal γ phases within the blocky B2 phase and at the B2/γ phase interface; (iii) lamellar degradation, it causes B2 phase to precipitate at the interface of lamellae; (iv) the precipitation of carbides, C element dissolves completely in the initial microstructure and precipitates dynamically during creep. Carbides can pin dislocations and induce the generation of twins, thereby enhancing the creep performances of alloys. Furthermore, an increase in temperature will promote microstructure evolution, resulting in increased dynamic recrystallization, larger-sized γ phase, more lamellar degradation and more carbides.