Based on damage caused by microstructure evolution during long-term thermal exposure to analyze and predict creep behavior of Ni-based single crystal superalloy

Abstract

The creep rupture life of a Ni-based single-crystal superalloy was evaluated under 980 °C/270 MPa after the superalloy was thermally exposed to temperatures of 900 °C, 950 °C, and 1100 °C for 100 h-500 h. The results showed that the coarsening rate of the γ′ phase increased with the thermal exposure temperature, and the activation energy of coarsening, Q, was ∼270.9 kJ/mol; this means that element diffusion controlled the coarsening of the γ′ phase. In addition, an increase in the thermal exposure temperature accelerated the precipitation process of the topologically close-packed (TCP) phase. Because of the degradation of the microstructure, the creep rupture life decreased from 113 h after thermal exposure at 900 °C to 95 h after exposure at 950 °C, and finally to 29 h after exposure at 1100 °C when exposed for 500 h. In view of the experimental results, the influence of the microstructure evolution on the creep rupture life was investigated in detail. Finally, a creep constitutive model based on the dislocation density was combined with a continuous damage model that considers the cavity damage to obtain a creep damage model. The creep remaining life prediction model of the single-crystal superalloy was established to predict the remaining life by introducing initial damage terms (the damage caused by the coarsening of the γ′ phase and that caused by the precipitation of the TCP phase during long-term thermal exposure, ωγ′ and ωTCP, respectively) to the creep damage model.