Oxidation-creep degradation mechanism of coating/superalloy with different Al and Cr content in coatings and the optimization strategy

As turbine inlet temperatures in advanced aeroengines continue to rise, achieving an optimal balance between the creep resistance and oxidation resistance of the coating/superalloy at 1200 °C has become increasingly difficult. In this study, multiscale analysis combined with thermodynamic calculations was employed to investigate the oxidation-creep behavior of NiCrAlYSi coatings, NiAl coatings, Al gradient NiCrAlYSi coatings and the uncoated superalloy. The results show that at 850 °C/500 MPa, the oxidation-creep degradation is the stress-sensitive damage manifesting as topologically close-packed (TCP) phase induced cracking. The coatings with varying Al and Cr contents exhibit sufficient plasticity to withstand creep loading until substrate fracture, without generating cracks themselves. At 1200 °C/80 MPa, the oxidation-creep degradation is the oxidation-diffusion damage. For the NiCrAlYSi coating, the formation of Cr-rich γ phase at the NiCrAlYSi coating/superalloy interface exerted little adverse effect on creep performance. Increasing the Al content in the coating enhances the oxidation resistance but reduces the creep performance of superalloy. For the Al gradient NiCrAlYSi coating, the IDZ consists of Cr-rich γ phases. Despite TCP precipitation, its SRZ retains the key γ/γ′ structure. In contrast, the NiAl coating exhibits a more degraded microstructure dominated by γ′ and TCP phases, accompanied by TCP reorientation, which is detrimental to the creep performance. Notably, the oxide scales with higher elastic modulus experience greater stress, which leads to the initiation of cracks. The pores form at the coating/superalloy interface cause crack deflection, thereby impeding crack penetration into the substrate. The significance of this study lies in managing Al/Cr diffusion to mitigate the creep degradation as much as possible. Tailoring the Al/Cr gradient distribution in NiCrAlYSi coatings is an effective strategy to synergistically enhance both oxidation resistance and creep resistance.