Evaluation of New High Entropy Alloy as Thermal Sprayed Bondcoat in Thermal Barrier Coatings

High-entropy alloys (HEAs) have great potential to be used as high-temperature materials and in coating material applications due to their combination of strength, ductility, thermal stability, wear, and oxidation resistance. In this work, a new HEA alloy based on NiCoCrAlSi composition was designed and deposited into metallic coatings by high-velocity oxy-fuel (HVOF) and air plasma spray (APS) processes, with the aim of developing new HEA bondcoats for thermal barrier coating (TBC) systems. The HEA coatings were analyzed for phases, microstructure and composition using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The results showed that the BCC phase is the major phase present in the as-applied HVOF coating that was vacuum diffusion treated at 1080 °C. APS coatings of the same composition HEA alloy showed a two-phase structure consisting of the L12 and BCC/B2 phases. The HEA bondcoats produced by HVOF were tested for oxidation resistance at 1050 °C in air, and for thermal cycling resistance of the TBC comprising of the HVOF-applied HEA bondcoat and standard 8YSZ ceramic topcoat. The results showed internal oxidation in the HEA bondcoat during the high-temperature oxidation exposure, but no significant coating failure after 100 thermal cycles at 1150 °C.