The planar-biaxial thermo-mechanical fatigue (TMF) behaviour of the nickel-base superalloy Inconel 718 was studied using cruciform specimens for temperatures between 400°C and 630°C. Eleven strain-controlled planar-biaxial tests were performed using two different batches of forged and heat-treated turbine disk materials. Selected mechanical proportional loading conditions, like biaxial strain ratios of 1 and 0.6, with temperature In-Phase and Out-of-Phase, and shear loading with one axis In-Phase and the other Out-of-Phase were studied at different mechanical strain amplitudes. For reference, additional uniaxial TMF tests were performed In-Phase and Out-of-Phase relative to the temperature.

The deformation behaviour of the material as well as the dynamical changing heat distribution of the cruciform specimens will be presented. The lifetimes of the tests were fitted using different multiaxial fatigue approaches. Results of finite element simulations were used to obtain the stress and strain fields of selected planar-biaxial TMF specimens. Additionally, the crack initiation mechanism, positions and crack paths were investigated.