High-temperature cyclic oxidation of conventional CSZ and CSZ + MoSi 2 self-healing thermal barrier coatings at 1100 °C

Abstract

Abstract Cyclic oxidation in thermal barrier coatings (TBCs) based on ZrO2 with MoSi2 + Al2O3 has gained increasing attention. The present study the atmospheric plasma spray (APS) process was used for applying a new dual-layer TBC (CSZ: ZrO2-25 wt.% CeO2-2.5 wt.% Y2O3 / MAC: MoSi2 + Al2O3 + CSZ) with enhanced oxidation resistance compared to the single-layer CSZ. CSZ/MAC and CSZ TBCs on NiCrAlY (bond coat) to nickel-based superalloy (IN738LC). The self-healing effects of the MAC overlayer were studied at 720°C for 5 and 10 h. The high-temperature cyclic oxidation tests were performed at 1100°C for 4 h in each cycle in an air-electric furnace and the samples were cooled during each cycle in the furnace. The role of MAC over layer in the improvement of the oxidation behaviour of CSZ was investigated through field emission scanning electron microscopy (FE-SEM/EDS), and X-ray diffraction (XRD) analyses. The coating was healed during the oxidation process due to the reaction of healing particles (MoSi2) on the surface of the sample with oxygen through the cracks at temperatures above 720°C. The MAC coatings showed improved oxygen diffusion resistance due to the filling and sealing effect. Thus, there is a low partial pressure of oxygen at the interface of BC-CSZ in the CSZ/MAC samples than in the CSZ samples. The low partial pressure of oxygen resulted in a slow growth rate of TGO, resulting in the improved oxidation and spallation resistance of the CSZ/MAC coatings. The results showed the higher oxidation resistance of dual-layer CSZ/MAC compared to the single-layer CSZ coating. Results of the study indicate that the MAC layer over the CSZ layer increased the coatings’ oxidation resistance for extended periods by preventing oxygen infiltration into the CSZ layer.