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Hybrid aerosol deposition (HAD) is a new coating method to deposit homogeneous nano-structured ceramic coatings. An accurate evaluation of the fabricated coating properties is required. In this study, α-Al2O3 fine powder was sprayed by HAD. The obtained coatings were dense and uniform with a nanocrystalline structure. An X-ray diffraction measurement revealed that the fabricated HAD Al2O3 coatings mainly consisted of α-Al2O3 phase. The hardness and Young's modulus of the HAD Al2O3 coatings were evaluated by a micro-Vickers method and a nanoindentation method using the Weibull distribution. The hardness of HAD Al2O3 coatings measured by micro-Vickers was ~1400 HV (~15 GPa). The variation of mechanical properties of HAD coatings measured by the nanoindentation method was extremely small compared to those of plasma-sprayed coatings, which also indicates that HAD coatings contain less pores and cracks than plasma-sprayed coatings.

Deposition of protective dense environmental barrier layers is a promising solution to improve the reliability and environmental durability of the next-generation turbines and other industrial applications. In this context, spraying of fine particles could enhance the formation of fine dense coating microstructures with improved properties. In AIST we are focusing on the spraying of the fine particles via different spraying technologies including suspension plasma spraying, as well as deposition of the fine solid particles directly by aerosol deposition (AD) and plasma-assisted aerosol deposition (so-called Hybrid Aerosol Deposition; HAD. The HAD is a new coating window to spray the fine ceramic particles via the implementation of a low-power rf-plasma source to assist the aerosol deposition at room temperature. This study introduced the feasibility of utilization of HAD as an outstanding technology for deposition of dense ceramic coatings on different substrate materials and 3D deposition capability. Highly dense and well-adhered Al2O3 coatings without obvious observable cracks and bulk-like properties were successfully fabricated on different substrate materials of SUS 304, Aluminium, Al2O3 and glass, via HAD of fine particles. The substrate material and its hardness significantly influenced the first deposition step, which determined the coating adhesion and properties. Furthermore, homogeneously uniform, dense, and crack-free coating with a strong adhesion has been fabricated successfully on cylindrical substrates with 6.3 mm diameter. During HAD spraying the plasma activated the surface of the particles without reaching to the molten state, then the activated particles impact and stuck with the substrate by room temperature impact consolidation mechanism. Therefore, the fabricated coatings had the same crystal structure as the starting feedstock powder, and the activated surface act as glue and improved the deposition efficiency and 3D capabilities. Herein, the deposition phenomena of HAD makes it as a promising candidate technology for development of environmental and sealing layers of highly dense microstructure, with the targeted crystalline phase structure, without stoichiometric composition nor phase transformation and improved deposition efficiency on multi-shape components in different fields such as environmental, thermal barrier coatings (TBCs), environmental barrier coatings (EBCs) and gas turbine applications.