Cyclic oxidation behavior of a multilayer composite coating for single-crystal superalloys

Highlights: • A multilayer composite coating was prepared, which comprised of alternating Ni + CrAlYSiHfN sub-layers and Al_xN sub-layers. • In cyclic oxidation, the oxide scale formed on multilayer coating exhibits good spallation resistance due to its lower CTE mismatch. • Ta_xO formed within the TGO of N5 substrate, and breaks the continuity and integrity of α-Al₂O₃ scale because of large PBR of Ta_xO. • The θ-to-α transformation of Al₂O₃ on multilayer coating leads to a slight decrease in resiudal stress in the initial oxidation stage. A multilayer composite coating, comprised of alternating Ni + CrAlYSiHfN sub-layers and Al_xN sub-layers, was manufactured by magnetron sputtering. The multilayer is composed of β-NiAl, α-Cr and AlN phases after annealing, and their volume fractions are 72 vol.%, 12 vol.% and 16 vol.%, respectively. Due to doping with nitrides, the CTE of multilayer coating is reduced to around 12.7*10⁻⁶/K. The lower CTE mismatch allows multilayer coating to exhibit good resistance to oxide scale spalling in thermal cycling at 1100 °C. The θ-to-α Al₂O₃ transformation in oxide scale caused a small drop of residual stresses on multilayer coating in initial oxidation stage.