Oxidation and hot corrosion characteristics of YSZ/ NiCoCrAlY electrophoretically deposited on IN-738

Gas turbines require high inlet temperatures to increase their efficiency, yet Ni-based superalloy components may not tolerate such harsh environment. Thermal barrier coatings (TBCs) are applied to reduce thermal loads and protect them in aggressive conditions. Conventional fabrication techniques, such as thermal spraying and EB-PVD, are costly and restricted by line-of-sight limitations. Electrophoretic deposition (EPD) offers a flexible, cost-effective alternative for applying TBCs on Ni-based components. In this study, a YSZ/NiCoCrAlY system was deposited by EPD on IN-738. The coated material was subjected to different sintering temperatures of 800 and 1100 °C and then exposed to cyclic oxidation at 1100 °C and type II hot corrosion at 700 °C. Oxidation studies showed parabolic kinetics, and the first sign of failure was observed after 19 cycles (152 h). XRD patterns revealed the YSZ phase stability, and SEM images showed that the NiCoCrAlY bond coat retained cohesion and adhesion with no cracks or spallation after successive oxidation cycles. However, XRD detected spinel formation at the NiCoCrAlY/YSZ interface, which promoted spallation at the interface. Hot corrosion tests revealed that YSZ coatings sintered at 1100 °C exhibited higher resistance than those sintered at 800 °C, due to improved densification and reduced salt penetration. EDS results confirmed chromium oxide formation at the NiCoCrAlY/YSZ interface, whicsh further suppressed elemental diffusion from the bond coat into the top coat. These results demonstrate that EPD can provide an effective and low-cost approach to fabricate durable TBCs with resistance to oxidation and hot corrosion, competitive with conventional techniques.