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<p>Degradation fatigue life and microstructure of single-crystal nickel superalloys were investigated. The in-phase thermomechanical fatigue (IP TMF) tests were conducted over three temperature ranges at mechanical strain amplitudes of 0.4-0.8%, using specimens oriented along the [001] crystallographic axis. Results reveal a marked reduction in fatigue life as the maximum test temperature increases, with the transition from dislocation-dominated deformation at 850&#xa0;°C to recrystallization-assisted crack propagation at 950&#xa0;°C and <i>γ</i>/<i>γ</i>′ boundary–controlled fracture at 1038&#xa0;°C. Concurrently, <i>γ</i>′ rafting, coarsening, and partial dissolution with rising temperature degrade the alloy’s resistance to creep-fatigue damage. Electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) analyses show that dynamic recrystallization creates high-angle grain boundaries that act as preferential oxidation pathways, accelerating crack growth. A novel creep-fatigue life prediction framework based on continuum damage mechanics (CDM) was proposed, demonstrating improved accuracy over conventional Coffin–Manson and Ostergren models by better capturing the coupled influence of cyclic plasticity and creep. This model highlights the critical role of dynamic recrystallization and <i>γ</i>′ precipitate behavior in fatigue life prediction. These findings provide mechanistic insight and a predictive framework for the design of single-crystal turbine alloys operating under complex service conditions.</p>

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Degradation of Fatigue Life and Microstructure in Single-Crystal Nickel Superalloy under In-Phase Thermomechanical Fatigue

  • 期刊论文

  • 发表日期：

    2026年1月13日

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  • Van Hung Dao,
  • Hee Soo Yun,
  • Thai Hung Le,
  • Hyusang Kwon,
  • Seung Hoon Nahm

摘要

Degradation fatigue life and microstructure of single-crystal nickel superalloys were investigated. The in-phase thermomechanical fatigue (IP TMF) tests were conducted over three temperature ranges at mechanical strain amplitudes of 0.4-0.8%, using specimens oriented along the [001] crystallographic axis. Results reveal a marked reduction in fatigue life as the maximum test temperature increases, with the transition from dislocation-dominated deformation at 850 °C to recrystallization-assisted crack propagation at 950 °C and γ/γ′ boundary–controlled fracture at 1038 °C. Concurrently, γ′ rafting, coarsening, and partial dissolution with rising temperature degrade the alloy’s resistance to creep-fatigue damage. Electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) analyses show that dynamic recrystallization creates high-angle grain boundaries that act as preferential oxidation pathways, accelerating crack growth. A novel creep-fatigue life prediction framework based on continuum damage mechanics (CDM) was proposed, demonstrating improved accuracy over conventional Coffin–Manson and Ostergren models by better capturing the coupled influence of cyclic plasticity and creep. This model highlights the critical role of dynamic recrystallization and γ′ precipitate behavior in fatigue life prediction. These findings provide mechanistic insight and a predictive framework for the design of single-crystal turbine alloys operating under complex service conditions.