Thermo-mechanical and Isothermal Fatigue of a Coated Columnar-Grained Directionally Solidified Nickel-Base Superalloy

The isothermal low-cycle fatigue (LCF) and the out-of-phase thermomechanical fatigue (TMF) behaviours of the directionally solidified nickel-base superalloy DS CM 247 LC, coated with a plasma-sprayed NiCrAlY-coating (PCA-1), were studied in detail. The investigations were performed on the uncoated, the coated substrate material and also on the pure coating material, in contrast to most existing work. The results of the isothermal LCF tests show that the fatigue life of the substrate/coating-composite is governed by the fatigue behaviour of the bulk coating material. The out-of-phase TMF cyclic deformation behaviour of the substrate/coating-composite reflects that of the components and is well described by an isostrain composite model. When the mechanical strain amplitudes experienced by the coating material are plotted against the fatigue life, the data on the coated material in isothermal LCF tests at the upper and lower temperatures of the TMF cycle, respectively, and in the TMF tests coincide. This gives further evidence that the behaviour of the coating materials governs that of the coated composite.