Abstract
AbstractAl2O3‐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.
Highlights
Amorphous materials have the characteristic of long-range disordered structure and short-range ordered clusters, and possess scientific and engineering interest for decades[1, 2]
The Al2O3-YAG amorphous ceramic coating was prepared by plasma spraying, and the main purpose was to study the formation mechanism of the amorphous phase in Al2O3-YAG coating to supply the guidance for the coating application
The granulation powders were further heat-treated to obtain Al2O3/YAG powders for the preparation of Al2O3-YAG amorphous ceramic coating, the preparation process can refer to our previous work[33]
Summary
Amorphous materials have the characteristic of long-range disordered structure and short-range ordered clusters, and possess scientific and engineering interest for decades[1, 2]. The glass transition temperature of the Al2O3-YAG amorphous coating was 905.5°C at 5 °C/min, and the initial crystallization activation energy of that was 807.8 kJ/mol by Kissinger method, so Al2O3-YAG amorphous ceramic coating had better high temperature microstructure stability than other 30 kinds of amorphous materials [21] This coating possessed greater crack propagation resistance and lower wear rate under severe wear conditions with high PV values (P: contact pressure; V: friction velocity) than conventional crystalline oxide ceramic coatings (such as Al2O3 coating, Al2O3- Cr2O3 coating)[25, 26]. Previous studies suggested that the formation mechanism of amorphous ceramic coatings was due to the thermal spraying with high enthalpy and ultra-fast cooling rate[26, 27]. The Al2O3-YAG amorphous ceramic coating was prepared by plasma spraying, and the main purpose was to study the formation mechanism of the amorphous phase in Al2O3-YAG coating to supply the guidance for the coating application
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