A mixture powder of ultra-high purity α-Al₂O₃(99.995%, AKP-53, Osaka, Japan) and ultrafine SiC(UF-0754, Ibiden Co., Ltd) was used as feedslock to deposit the nanocomposite coatings by plasma spraying in this study. Individual nanopartides could nol be plasma sprayed directly due to their low mass an...
A mixture powder of ultra-high purity α-Al₂O₃(99.995%, AKP-53, Osaka, Japan) and ultrafine SiC(UF-0754, Ibiden Co., Ltd) was used as feedslock to deposit the nanocomposite coatings by plasma spraying in this study. Individual nanopartides could nol be plasma sprayed directly due to their low mass and bad flowability. With the aid of Poly-Elbylene Glycol binder (PEG) and Pol-Methaclylic acid-sodium salt dispersant (PMAA), the nanoparticles were reconstituted into micrometer-sized granules by spray drying process before the plasma spraying. In order to determine the effect of nanosized SiC on microstructure and mechanical properties of Al₂O₃-SiC nanocomposite coatings, the amount of SiC was varied from 0 10 20 vol.% of nanocomposite powders. X-Ray Diffraction (XRD) analysis was used to identify phase composition of the powder and the as-sprayed coating. The morphologies of surface and cross-section of the plasma sprayed Al₂O₃-SiC nanocomposite coatings were observed by Scanning Electron Microscopy (SEM). SEM micrographs showed that Al₂O₃-SiC powders were almost melted. Vicker's microhardness was measured on the cross sections. Moreover, the wear-resistant properties of Al₂O₃- SiC nanocomposite coatings were studied. The worn surfaces were observed by SEM in order to find out the sliding wear mechanism of the Al₂O₃-SiC nanocomposite coalings. Also surface roughness of the plasma sprayed coating layers were investigated and cohesive force of the coating layers was measured. Coating thickness was measured through the Large Scaled Measuring Microscope. Pprosities of coated layers were measured. Dry in oven process aids spray dried powder flowability. However, time in oven of the drying process is not important factor. Base on SEM, XRD, size-distribution results, productivity and the price of binder, 3wt%PEG binder is better than PVA binder for spray drying powder both in the sufficient mechanical strength of granules and in the operating process. On one hand, there is insignificant changing of powders phases with atomizing factor of spray drying process. On the other hand, atomizing gives big influences on the size, quality and quantity of granules. Although the main phases of powders are α-Al₂O₃, and α-SiC, there are some changed in phase of powder when changed the pump-speed. However, this phase was unimportant. 70ml³/h of pump speed gave the best productivity. Inlet temperature didn't give noticeable influence on the shape, size, and density of granules of spray-dried 95vol.%Al₂O₃-5vol.%SiC powder. Only productivity of powders showerl some changes with inlet tempernture. 100kPa of atomizing, 70ml³/h of pump-speed and 155℃ of inlet temperature factor was the best choice for spray drying 95vol.%Al₂O₃-5vol.%SiC powders. Surface roughness revroled that the smoothest surface was made when Ar=70[NLPM]. The plasma spraying primaly argon gas influenced not only on the microstructure of Al₂O₃-SiC coatings, but also on the deposition efficiency, thickness of coating. Although, the XRD spectra of coatings showed that the phase compositions were changed after the plasma spraying. However, unlike the primary Ar gas, H₂ gas didn't have noticeable effect on plasma spray coating. Under lower spraying power (550[A]×80[V]=47.79[KW]), the Al₂O₃-SiC powders melted (resulting in wen spread particles hence dense-thin-coating). It could be found that the molten degree of powders depended on the spraying power. XRD spectra of coatings look similar; however, the SEM micrographs of coating surfaces showed the different morphologies with different spray distances. The deposition efficiency of spray-dried powders decreased with increasing of spraying distance. The best parameters of plasma spray process for 95vol%Al₂O₃-5vol%SiC nano-composites coatings were 75[NLPM] Ar, 12[NLPM]H₂550[A]×80[V] of power and 120[mm]of spray distance. XRD spectra of plasma spray coatings showed the strong decomposed of alumina and silicon carbide in very high temperature of plasma flame to make new combinations. The Vicker's Hardness of coated layers decreased with increasing SiC content in the Al₂O₃-SiC nanocomposites. Vicker's hardness ranged from 1.8 to 5Gpa. The average porosity ranged from 4 to 27%, and it increased with SiC content. 100vol%Al₂O₃-0vol%SiC coating was the best coating with highest hardness(5GPa), the better toughness and denser microstructure as well as more homogenous distribution of pores in this work. The present investigation indicated that the porosity of Al₂O₃-SiC coatings was directly proportional to the SiC content.
A mixture powder of ultra-high purity α-Al₂O₃(99.995%, AKP-53, Osaka, Japan) and ultrafine SiC(UF-0754, Ibiden Co., Ltd) was used as feedslock to deposit the nanocomposite coatings by plasma spraying in this study. Individual nanopartides could nol be plasma sprayed directly due to their low mass and bad flowability. With the aid of Poly-Elbylene Glycol binder (PEG) and Pol-Methaclylic acid-sodium salt dispersant (PMAA), the nanoparticles were reconstituted into micrometer-sized granules by spray drying process before the plasma spraying. In order to determine the effect of nanosized SiC on microstructure and mechanical properties of Al₂O₃-SiC nanocomposite coatings, the amount of SiC was varied from 0 10 20 vol.% of nanocomposite powders. X-Ray Diffraction (XRD) analysis was used to identify phase composition of the powder and the as-sprayed coating. The morphologies of surface and cross-section of the plasma sprayed Al₂O₃-SiC nanocomposite coatings were observed by Scanning Electron Microscopy (SEM). SEM micrographs showed that Al₂O₃-SiC powders were almost melted. Vicker's microhardness was measured on the cross sections. Moreover, the wear-resistant properties of Al₂O₃- SiC nanocomposite coatings were studied. The worn surfaces were observed by SEM in order to find out the sliding wear mechanism of the Al₂O₃-SiC nanocomposite coalings. Also surface roughness of the plasma sprayed coating layers were investigated and cohesive force of the coating layers was measured. Coating thickness was measured through the Large Scaled Measuring Microscope. Pprosities of coated layers were measured. Dry in oven process aids spray dried powder flowability. However, time in oven of the drying process is not important factor. Base on SEM, XRD, size-distribution results, productivity and the price of binder, 3wt%PEG binder is better than PVA binder for spray drying powder both in the sufficient mechanical strength of granules and in the operating process. On one hand, there is insignificant changing of powders phases with atomizing factor of spray drying process. On the other hand, atomizing gives big influences on the size, quality and quantity of granules. Although the main phases of powders are α-Al₂O₃, and α-SiC, there are some changed in phase of powder when changed the pump-speed. However, this phase was unimportant. 70ml³/h of pump speed gave the best productivity. Inlet temperature didn't give noticeable influence on the shape, size, and density of granules of spray-dried 95vol.%Al₂O₃-5vol.%SiC powder. Only productivity of powders showerl some changes with inlet tempernture. 100kPa of atomizing, 70ml³/h of pump-speed and 155℃ of inlet temperature factor was the best choice for spray drying 95vol.%Al₂O₃-5vol.%SiC powders. Surface roughness revroled that the smoothest surface was made when Ar=70[NLPM]. The plasma spraying primaly argon gas influenced not only on the microstructure of Al₂O₃-SiC coatings, but also on the deposition efficiency, thickness of coating. Although, the XRD spectra of coatings showed that the phase compositions were changed after the plasma spraying. However, unlike the primary Ar gas, H₂ gas didn't have noticeable effect on plasma spray coating. Under lower spraying power (550[A]×80[V]=47.79[KW]), the Al₂O₃-SiC powders melted (resulting in wen spread particles hence dense-thin-coating). It could be found that the molten degree of powders depended on the spraying power. XRD spectra of coatings look similar; however, the SEM micrographs of coating surfaces showed the different morphologies with different spray distances. The deposition efficiency of spray-dried powders decreased with increasing of spraying distance. The best parameters of plasma spray process for 95vol%Al₂O₃-5vol%SiC nano-composites coatings were 75[NLPM] Ar, 12[NLPM]H₂550[A]×80[V] of power and 120[mm]of spray distance. XRD spectra of plasma spray coatings showed the strong decomposed of alumina and silicon carbide in very high temperature of plasma flame to make new combinations. The Vicker's Hardness of coated layers decreased with increasing SiC content in the Al₂O₃-SiC nanocomposites. Vicker's hardness ranged from 1.8 to 5Gpa. The average porosity ranged from 4 to 27%, and it increased with SiC content. 100vol%Al₂O₃-0vol%SiC coating was the best coating with highest hardness(5GPa), the better toughness and denser microstructure as well as more homogenous distribution of pores in this work. The present investigation indicated that the porosity of Al₂O₃-SiC coatings was directly proportional to the SiC content.
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