Fatigue life of cast Inconel 713LC with/without protective diffusion coating under bending, torsion and their combination

Fatigue behaviour of cylindrical specimens made of cast Inconel 713LC nickel-based superalloy with/without diffusion aluminide and Cr-modified aluminide protective coatings was studied under bending, torsion and combined bending–torsion loading regimes. Experiments were conducted at room temperature by using sinusoidal loading of a frequency f ≈ 30 Hz. It was found that the presence of either coating system enhances the high cycle fatigue strength for all tested loading regimes. In the low cycle fatigue region, the fatigue strength was slightly improved for torsional loading, while it was almost the same or modestly lower for loading regimes with non-zero bending component. This behaviour seems to be linked to different nucleation efficiency of secondary-phase particles within the diffusion zone. Acquired experimental data were also used to evaluate predictive capabilities of stress-based multiaxial fatigue failure criteria proposed by Gough, Matake and Crossland that were selected as representatives of main multiaxial fatigue failure prediction classes. Results revealed that, for a given material and loading conditions, the Matake criterion based on a critical plane approach provides the best fatigue life data estimations most of which are within a factor of two bandwidth.