Search

Al2O3‐YAG (Al5Y3O12) amorphous ceramic coatings exhibit excellent crack propagation resistance under harsh wear services due to the amorphous phase contributing to the plastic deformation performance of the coating. However, the formation mechanism of the amorphous phase is ambiguous. This study mainly investigated the formation mechanism of Al2O3‐YAG amorphous coating prepared by atmospheric plasma spraying from the perspective of crystallization chemistry. Nano and microsized powders with low eutectic point ratio were selected as feedstock for comparison. X‐ray diffraction, scanning electron microscope, and electron backscattered diffraction were used to analyze the phase composition, morphologies, phase distribution, and structure of the coating. It is concluded that the significant thermodynamically stable structure of polycompound with high coordination numbers of cations prioritized crystallizing in the Al2O3‐YAG melt, but it needed more time to crystallize and hardly crystallized in the limited time during plasma spraying. Therefore, the selection of as‐sprayable powder should also be considered the critical factor for preparing amorphous coatings. The nanoscale or submicro scale powder distributed uniformly with low eutectic point ratio was chosen as the feedstock to ensure the powder droplets diffuse sufficiently during deposition. [ABSTRACT FROM AUTHOR]

Al2O3-YAG amorphous ceramic coating is expected to apply to harsh wear service due to its excellent crack propagation resistance, but the crystallization of this coating may affect its service stability. Therefore, the crystallization behavior of the Al2O3-YAG coating prepared by atmospheric plasma spray (APS) was investigated in this study. The results showed that this coating had excellent microstructure stability over a broad temperature range and had a higher activation energy during non-isothermal crystallization process. The isothermal DSC curves showed that the crystallization process of this coating was controlled by the change in external thermodynamic conditions. The grain growth mechanism for α-Al2O3 and YAG was from three-dimensional direction bulk growth to one-dimensional direction flake thickening. The calculated fragility index showed that the amorphous ceramic coating had better stability and higher plastic deformation capacity than other typical brittle materials at its critical temperature range. [ABSTRACT FROM AUTHOR]