Mechanical degradation behavior and γ′ coarsening mechanism of a Ni-based superalloy during long-term high-temperature thermal exposure
Zhaotian Wang, Yongquan Ning, Hao Yu, Baoyun Zhang, Bingchao Xie, Shuo Huang, Wenyun Zhang, Beijiang Zhang
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 of 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.