Thermal gradient mechanical fatigue assessment of a nickel-based superalloy

Jingyu Sun,Huang Yuan,Michael Vormwald

doi:10.1016/j.ijfatigue.2020.105486

Abstract

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.

Highlights

The nickel-base superalloy Inconel 718 is widely used in the gas turbine engines [1]
The results showed that the temperature gradients had a remarkable influence on the thermomechanical fatigue (TMF) lifetime
The isothermal fatigue (IF) tests were performed at 650°C, and the in-phase thermomechanical fatigue (TMF-IP) and the out-of-phase thermomechanical fatigue (TMF-OP) tests were carried out with a temperature range of 300~650°C, as introduced in [10,16]

Summary

Introduction

The nickel-base superalloy Inconel 718 is widely used in the gas turbine engines [1]. Isothermal fatigue (IF) tests were commonly used to predict the lifetime of gas turbine components, which generally work under varying thermomechanical loading conditions. The turbine parts suffer from thermomechanical fatigue damage caused by the varying loads and temperatures. In the TGMF tests the thermal stress is induced by the temperature gradient and cannot be represented by the applied mechanical stress, which is the major difference to the TMF. To give a reasonable prediction of the TGMF life, the temperature gradient has to be included in the life model in a suitable way. Based on the TMF model [10], a correction term relying on the temperature gradient is to be included.

Methods

Results

Conclusion