Abstract:During the high-temperature smelting of highly active alloys, the graphite crucible will react with the alloy, causing carbon pollution and affecting the purity of the melt and the performance of the workpiece. Therefore, a Graphite barrier coating (GBC) needs to be prepared on the surface of the graphite substrate to protect the graphite. The GBC coating can effectively prevent the direct contact between the liquid active alloy and the graphite crucible, playing the roles of diffusion inhibition, thermal shock resistance and corrosion resistance. In this study, the atmospheric long laminar flow plasma spraying technology (ALPS) was adopted to prepare GBC on the inner wall of graphite. Y2O3 and CaZrO3 coatings were successfully deposited on the inner walls of graphite crucibles with inner diameters of 105 mm and 55 mm. The coating was treated at 1300 ℃ for 1 hour. The structure, elastic modulus, hardness and surface roughness of the coating after high-temperature and long-term holding were investigated by scanning electron microscopy (SEM), nanoindentation instrument and laser confocal microscopy. The results show that after long-term holding at 1300 ℃, the porosity of the Y2O3 and CaZrO3 coatings on the inner surface of the crucible with an inner diameter of 105 mm is 13.88% and 17.05% respectively. The elastic moduli are 120.76 and 157.27 GPa respectively. The hardness is 5.79 and 9.31 GPa respectively. The surface roughness (Sa) was 12.3 μm, and the porosity of the Y2O3 and CaZrO3 coatings on the inner surface of the 55 mm crucible was 6.31% and 6.63%, respectively. The elastic moduli are 114.47 and 152.69 GPa respectively. The hardness is 5.45 and 8.26 GPa respectively. The surface roughness (Sa) is 11.5 μm. No macroscopic peeling was observed on the inner wall coatings. The deposition process of powder particles and the failure process of the coating under high-temperature and long-term holding were analyzed when preparing the inner surface coating by ALPS technology.