Thermal gradient mechanical fatigue assessment of a nickel-based superalloy

In the present work, a radiation heating system was developed to simulate thermal gradient mechanical fatigue (TGMF) loads in turbines. The specimen is externally heated by radiation and internally cooled by compressed air. Experiments showed that the TGMF life of the nickel-based superalloy is significantly shorter than that of the thermo-mechanical and the isothermal fatigue, although the thermal stress is small. It was confirmed that the conventional fatigue models generated seriously deviations and could not catch effects of the thermal gradients. The modified TGMF model introduced a correction term of the temperature gradient effects and can describe the TGMF lifetime of Inconel 718 reasonably. The new model provides a uniform description of isothermal and complex thermo-mechanical fatigue.