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

The creep rupture life of a Ni-based single-crystal superalloy was evaluated under 980 degrees C/270 MPa after the superalloy was thermally exposed to temperatures of 900 degrees C, 950 degrees C, and 1100 degrees C for 100 h-500 h. The results showed that the coarsening rate of the gamma ' phase increased with the thermal exposure temperature, and the activation energy of coarsening, Q, was similar to 270.9 kJ/mol; this means that element diffusion controlled the coarsening of the gamma ' 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 degrees C to 95 h after exposure at 950 degrees C, and finally to 29 h after exposure at 1100 degrees 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 gamma ' phase and that caused by the precipitation of the TCP phase during long-term thermal exposure, omega gamma ' and omega (TCP), respectively) to the creep damage model.