Ceramic Coatings Deposited from Fine Particles by Different Spraying Processes
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Ceramic Coatings Deposited from Fine Particles by Different Spraying Processes Mohammed Shahien1,2 • Masato Suzuki1 • Kentaro Shinoda1 • Jun Akedo1
Submitted: 11 February 2020 / in revised form: 12 August 2020 ASM International 2020
Abstract Plasma spraying of fine particles promises uniform microstructure and improved properties for ceramic coatings due to the formation of small splats with reduced residual stress and pore size. Although spraying fine particles is challenging due to the poor rheological properties of particles (e.g., low flowability and agglomeration), the potential improvements to the coatings make it an attractive option. In this study, we discussed the feasibility of fine particle spraying via three different spraying techniques, namely low-power direct current (DC) plasma spraying, axial suspension plasma spraying (ASPS), and plasma-assisted aerosol deposition or hybrid aerosol deposition (HAD). Low-power DC plasma was sufficient to melt and deposit fine particles in an ambient atmosphere without using a liquid carrier. The fabricated coatings had similar features to those of ASPS coatings of small splats (5–8 lm in diameter without internal cracks). The fabricated coatings by the low-power DC plasma showed almost equivalent properties to that of the conventional plasmasprayed coating while providing low energy consumption. Fine particles deposited via the HAD process led to the coatings with improved microstructure without pores or cracks. During the HAD process, particle melting was not required for deposition, and using the plasma assisted the surface activation and improved the deposition efficiency of the aerosol deposition process. The fabricated HAD
& Mohammed Shahien [email protected]; [email protected] 1
Advanced Coating Technology Research Center, National Institute of Advanced Industrial Science, and Technology (AIST), Tsukuba, Japan
2
Advanced Materials Department, Central Metallurgical Research and Development Institute (CMRDI), Cairo, Egypt
coating revealed improved microstructure with the highest hardness, Young’s modulus, and adhesion strength and lack of pores or cracks compared to the coatings fabricated by other plasma spray techniques. In addition, similarities and differences among the techniques for spraying fine ceramic particles were investigated. Keywords atmospheric low-power DC plasma spraying axial suspension plasma spraying (ASPS) coating properties fine particle plasma spraying (FPPS) hybrid aerosol deposition (HAD) plasma-assisted aerosol deposition (PAD)
Introduction Plasma spray deposition is a well-known, widely used technique among surface coating approaches (Ref 1). In general, several tens of micrometer-sized (30–100 lm) particles with good flowability are used as a starting feedstock (Ref 2-5). During spraying, the feedstock powder is introduced into a plasma jet to form liquid droplets. These molten droplets are simultaneously accelerated by the jet flow toward the substrate surface. The molten or semi-molten drop
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