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A study of small crack propagation behavior in a single crystal Ni based superalloy under TMF conditions

Single crystal Ni based superalloys are widely used for turbine blades and vanes in power generation gas turbines. During service, these components are subjected to complex stress and temperature cycles, known as thermo-mechanical fatigue (TMF) loading, which can lead to crack propagation and subsequent damage.  To ensure an accurate prediction of TMF life, it is crucial to clarify the mechanisms of small crack propagation under such conditions.

In this study, small crack propagation tests were performed under TMF conditions with varied phase angles between temperature and mechanical loading, as well as different dwell times, to examine their effects on crack propagation behavior. The experimental results indicated that elastic deformation dominated the cyclic response…

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Single crystal Ni based superalloys are widely used for turbine blades and vanes in power generation gas turbines. During service, these components are subjected to complex stress and temperature cycles, known as thermo-mechanical fatigue (TMF) loading, which can lead to crack propagation and subsequent damage.  To ensure an accurate prediction of TMF life, it is crucial to clarify the mechanisms of small crack propagation under such conditions.

In this study, small crack propagation tests were performed under TMF conditions with varied phase angles between temperature and mechanical loading, as well as different dwell times, to examine their effects on crack propagation behavior. The experimental results indicated that elastic deformation dominated the cyclic response macroscopically. However, when crack growth rates were correlated with the fatigue J-integral range calculated from macroscopic hysteresis loops, ∆Jf, the data exhibited a broad scatter, suggesting the conventional nonlinear fracture mechanics parameters are insufficient to characterize small crack propagation under TMF. To address this, finite element analysis was also conducted to evaluate the crack tip opening displacement range (ΔCTOD). A strong correlation was found between crack growth rate and ΔCTOD across the tested conditions. These findings demonstrate that the local plasticity and creep deformation around the crack tip may play a critical role in governing fatigue crack propagation in single crystal superalloy under the TMF loading.

Reference
LCF10-2026-008

Title
A study of small crack propagation behavior in a single crystal Ni based superalloy under TMF conditions
Author(s)
M. Arai, Y. Yamazaki
DOI
10.48447/LCF10-2026-008
Event
Tenth International Conference on Low Cycle Fatigue (LCF-10)
Year of publication
2026
Publication type
conference paper (PDF)
Language
English
Keywords
Thermo-mechanical fatigue,small crack,single crystal superalloy