Mechanical degradation behavior and γ′ coarsening mechanism of a Ni-based superalloy during long-term high-temperature thermal exposure

Abstract

Aero engine design necessitates crucial components, such as turbine discs, to be highly stable in high-temperature environments. Therefore, the accurately determining of the mechanical properties and microstructure evolution of these components under long-term high-temperature exposure is ofs significant engineering and scientific value. Herein, we systematically analyzed the microstructure and performance evolution of a Ni-based superalloy during long-term high-temperature exposure, explored the relationship between service conditions and yield strength, and introduced novel strength decay factors, namely temperature (|α|) and time (|β|) decay factors. |α| was strongly positively correlated with the exposure temperature, whereas |β| exhibited a more complex behavior and was more affected by the microstructure before thermal exposure, especially at low temperatures (650–700 °C). Microstructural analysis revealed minimal changes in average grain size and Σ3 twin boundaries following long-term thermal exposure. However, γ′ particles coarsened after thermal exposure, particularly at higher temperatures and longer exposure times. The coarsening process under different conditions was examined using Lifshitz–Slyozov–Wagner and trans-interface diffusion-controlled models. The coarsening of γ′ particles led to mechanical degradation, as the critical failure stress decreased with increasing γ′-particle size.