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.
Highlights
Ni-based single-crystal superalloys have long been used as important materials for turbine blades because of their excellent creep, fatigue, and corrosion resistance.[1,2,3] To a great extent, these properties are attributed to the microstructure of the single-crystal superalloy, which is composed of a high volume fraction of cubic ordered γ′ precipitates embedded in a disordered γ matrix phase
At the thermal exposure temperature of 1100 ○C, the creep rupture life in the first 100 h of exposure was reduced by ∼59%
After thermal exposure for 500 h at different temperatures, the creep rupture life rapidly dropped from 113 h to 95 h and to 29 h as the exposure temperature increased from 900 ○C to 950 ○C and to 1100 ○C, respectively, which were decreases of ∼35.8%, 46% and 83.5% compared to that of the original alloy, respectively
Summary
Ni-based single-crystal superalloys have long been used as important materials for turbine blades because of their excellent creep, fatigue, and corrosion resistance.[1,2,3] To a great extent, these properties are attributed to the microstructure of the single-crystal superalloy, which is composed of a high volume fraction of cubic ordered γ′ precipitates embedded in a disordered γ matrix phase. The high centrifugal stress and long-term service inevitably lead to microstructure degradation, including the coalescence and coarsening of the γ′ precipitates, and the precipitation of the topologically closedpacked (TCP) phase.[4,5,6,7,8] These changes have a significant impact on the elevated temperature creep properties of the turbine blade materials. The γ/γ′ microstructure could remain stable, and it was not easy to activate the dislocation movement, thereby limiting the occurrence and propagation of dislocations.[9,10,11] at elevated temperatures, the creep deformation depended on the movement of dislocations in the γ matrix channel
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