Effect of alumina-silica-zirconia eutectic ceramic thermal barrier coating on the low cycle fatigue behaviour of cast polycrystalline nickel-based superalloy at 900 °C

Cylindrical specimens of nickel-based superalloy Inconel 713LC in an as-cast condition and coated with a thermal barrier coating (TBC) system consisting of a CoNiCrAlY bond coat and an eutectic ceramic alumina-silica-zirconia top coat were cyclically loaded under strain control at 900 °C in air. TBC was deposited using atmospheric plasma spray and water-stabilised plasma spray techniques for the bond coat and the top coat, respectively. The microstructure of the substrate material and the TBC was characterised and the hardness of TBC was measured. The cyclic stress-strain response and fatigue life of both materials were assessed. The stress response of the TBC-coated superalloy is lower than the uncoated superalloy. The detrimental effect of TBC on the Basquin curve is documented. The specimen section and fracture surface observations revealed fatigue damage mechanisms in both the TBC-coated and uncoated specimens, and that finding helps explain the differences in the fatigue behaviour of both materials.