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Purpose: The purpose of this study is to describe the mechanism of single-crystal high-temperature creep deformation, predict the creep life more accurately and study the creep constitutive and lifetime models with microstructure evolution. Design/methodology/approach: The mechanical properties of nickel-based single-crystal superalloy are closely related to the γ' phase. Creep tests under four different temperature and stress conditions were carried out. The relationship between creep temperature, stress and life is fitted by numerical method, and the creep activation energy is obtained. The creep fracture surface, morphology and evolution of strengthening phase (γ') and matrix phase (γ) during different creep periods were observed by scanning electron microscope. With the increase of creep temperature, the rafting time is advanced. The detailed morphology and evolution of dislocations were observed by transmission electron microscope (TEM). Findings: With the increase of creep temperature, the rafting time is advanced. The detailed morphology and evolution of dislocations were observed by TEM. Dislocations are mainly concentrated in the γ channel phase, especially at high temperature and low stress. Originality/value: A creep constitutive model based on the evolution of γ' phase size and γ channel width was proposed. Compared with the experimental results, the predicted creep life is within 1.4 times error dispersion band. [ABSTRACT FROM AUTHOR]

The present study investigates the creep behavior and deformation mechanism of a third-generation single-crystal Ni-based superalloy at 1170 °C under a range of stress levels. Scanning electron microscopes (SEM) and transmission electron microscopes (TEM) were employed to observe the formation of a rafted γ′ phase, which exhibits a topologically close-packed (TCP) structure. The orientation relationship and elemental composition of the TCP phase and matrix were analyzed to discern their impact on the creep properties of the alloy. The primary deformation mechanism of the examined alloy was identified as dislocation slipping within the γ matrix, accompanied by the climbing of dislocations over the rafted γ′ phase during the initial stage of creep. In the later stages of creep, super-dislocations with Burgers vectors of a<010> and a/2<110> were observed to shear into the γ′ phase, originating from interfacial dislocation networks. Up to the fracture, the sequential activation of dislocation shearing in the primary and secondary slipping systems of the γ′ phase occurs. As a consequence of this alternating dislocation shearing, a twist deformation of the rafted γ′ phase ensued, ultimately contributing to the fracture mechanism observed in the alloy during creep. [ABSTRACT FROM AUTHOR]

In the present study, the microstructure and the mechanical properties of GTD-111 nickel-based superalloy were investigated. The alloy was in service as the GE-MS9001 gas turbine 1st stage rotating blade for 105,000 hours at a temperature between 950 to 1000 °C. Two sets of samples were extracted from the airfoil and the root of the blade. Then, they were compared for the microstructural and the mechanical properties changes after the high temperature service. Stress-rupture and Charpy V-notch (CVN) tests were conducted on the samples at 871 °C and two temperatures of 25 and 900 °C, respectively. The microstructure and the fracture surface of the samples were analyzed using a scanning electron microscope (SEM). The results showed degradation in the microstructure and the mechanical properties of the airfoil compared to those of the root due to the long-term service at elevated temperatures. The loss in mechanical properties was due to the coarsening of γ' precipitates and the formation of brittle phases in the grain boundaries. [ABSTRACT FROM AUTHOR]