High temperature stress relaxation and combined cycle fatigue tests of superalloys for gas turbine blades

In gas turbine engines for aerospace propulsion, the assessment of the fatigue damage mechanisms due to the interaction of high cycle fatigue (due to vibration phenomena) and low cycle fatigue (due to ground-air-ground major engine cycling) are of paramount importance for the structural integrity of the components. Moreover, the fatigue damage may be further accelerated by the interaction with creep and stress relaxation due to the exposure to high temperatures. In order to experimentally evaluate the material performance in this highly demanding environment, a number of combined cycle fatigue (CCF) and low cycle fatigue (LCF) tests with dwell, where stress relaxation plays an important role, have been carried out on a polycrystalline nickel superalloy, at temperatures up to 870 °C. Comparison of the CCF and the LCF tests with dwell, in which the creep-fatigue damage mechanisms can be highlighted, with conventional LCF tests is also presented.