Effect of thermal barrier coatings on the fatigue behavior of a single crystal nickel-based superalloy: Mechanism and lifetime modeling

Coatings are typically used to protect engineering materials from oxidation, corrosion, and erosion. However, it also changes the surface condition of substrate materials and causes a mechanical mismatch between the substrate and coatings. This study investigated the effect of thermal barrier coatings (TBCs) on the fatigue behavior of a second-generation single crystal (SX) Ni-based superalloy. The experimental results showed that the impact of the TBCs on the fatigue lifetime was loading-dependent. The coating was beneficial under low stresses but had no effect under high stresses. The scanning electron microscope (SEM) observation showed that the TBCs did not change the fatigue crack initiation location. For most coated and uncoated samples, the cracks are more likely to generate from the internal defects in the substrate. In addition, an equivalent strain energy density-based lifetime prediction model was proposed for coated samples. The prediction capability of the proposed model agreed well with experimental results. This study could provide insight into the failure mechanism for TBCs-coated single-crystal superalloys.