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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]

Abstract: Crystallization kinetics of the newly developed Al2O3‐Y3Al5O12 (YAG) amorphous ceramic coating fabricated by atmospheric plasma spraying (APS) were investigated via differential scanning calorimetry (DSC) under non‐isothermal conditions. The phase compositions and microstructure of the as‐sprayed coating were characterized by X‐ray diffraction (XRD) and Scanning electron microscopy (SEM). The glass transition temperature Tg, the onset temperature of crystallization Tc and the peak temperature of crystallization Tp presented heating rate dependence. The related kinetic parameters of activation energies (Eg, Ec, Ep) and Avrami exponents (n) were quantified using various methods including Kissinger, Augis–Bennett, Ozawa and Matusita–Sakka, etc., to understand the phase transition mechanism and crystallization process in depth. A series of parameters including devitrification interval ΔT, thermal stability (Tc, Ec), nucleation resistance Ec/RTg and fragility index F were quantified in order to evaluate the nucleation mechanism, crystallization behavior and thermal stability of Al2O3‐YAG amorphous ceramic coating. Excellent thermal stability was witnessed in the studied coating. Furthermore, the YAG crystalline phases can be reasonably controlled and independently precipitated from the amorphous matrix via proper annealing. [ABSTRACT FROM AUTHOR]

The effects of Mo doping on LaCaCrO oxide ceramics synthesized using a solid state reaction method were systematically investigated by thermogravimetric and differential thermal analysis, X-ray diffraction, 3D laser microscopy, UV-Vis spectrophotometry, and infrared diffused reflection measurement. Through these experiments, it was found that the structure, morphology, and spectral properties of the ceramic powders depend on the concentration of Mo ions. Identification and quantification of crystalline phases using Rietveld refinement revealed the presence of Mo-doped calcium lanthanum chromites and calcium molybdate (CaMoO) in doped oxides with ≤0.5 at% Mo, whereas LaCrO, CaMoO and LaMoO were formed at higher concentrations. The mean surface roughness of all the samples was around 0.2 μm, and therefore had little influence on the solar absorptance and infrared emissivity. Calculated values obtained by integrating the spectra identified a low near infrared reflectivity (0.47) with 81 % solar absorptance, indicating the possibility of selectively controlling the spectral properties at a specific wavelength to create functional ceramics with variable near infrared reflectivity for use in solar applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis of TiB2–TiC–Al2O3/Al composite coatings on Mg alloy by RPS. [•] Microstructure and properties of the RPS coatings were characterized. [•] The coatings consist of TiB2, TiC, Al2O3 and/or excess Al without by-products. [•] The coatings display dense structure and good interfacial bonding with substrate. [•] The coatings provide good protection for the Mg alloy against wear and corrosion. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis of TiC–TiB2-based Co cermets by way of SHS using a Co–Ti–B4C system. [•] Reaction behavior, microstructure and formation mechanism were investigated. [•] Fabrication of TiC–TiB2-based Co cermet coatings by APS using the SHS powders. [Copyright &y& Elsevier]