Effect of La on Formation Process and Resistance to High-Temperature Oxidation of Aluminizing Coating
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An Fe-Ni-Co based superalloy Incoloy 909 (Incoloy 909) has been used for gas turbine engine component material. This alloy is susceptible to high temperature oxidation and corrosion because of the absence of corrosion resistant Cr. For the improvement of durability of the component of Incoloy 909 aluminizing-chromate coating by pack cementation process has been investigated at relatively low temperature of about $550^{\circ}C$ to protect the surface microstructure and properties of Incoloy 909 substrate. As a previous study to aluminizing-chromate coating by pack cementation of Incoloy 909, the optimal aluminizing process has been investigated. The size effects of source Al powder and inert filler $Al_O_3$ powder and activator selection have been studied. And the dependence of coating growth rate on aluminizing temperature and time has also been studied. The optimal aluminizing process for the coating growth rate is that the mixing ratio of source Al powder, activator $NH_4Cl$ and filler $Al_O_3$ are 80%, 1% and 19% respectively at aluminizing temperature $552^{\circ}C$ and time 20 hours.
Incoloy
Cementation (geology)
Chromate conversion coating
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Studies have shown that platinum modified aluminide coatings can exhibit a range of structural variations depending on initial platinum thickness, prealuminizing heat treatment, aluminizing cycle, and postcoating heat treatment. It had been speculated earlier that such structural variation could account at least in part for some of the reported variation of performance of these coatings. A series of archetype structures was prepared on IN738 by two aluminizing processes: (i) low aluminum activity and (ii) high aluminum activity; and tested at 900 °C under conditions producing so called Type I high temperature hot corrosion. The results of the present investigation showed that the addition of platinum greatly improved the hot corrosion resistance. It is observed that the low aluminum activity process has better corrosion resistance than that of the high aluminum activity process. It is also found that the surface degradation of both aluminizing processes is quite severe when the specimens were given prolonged prealuminizing diffusion heat treatment. Microstructural observation revealed a significant difference in coating thickness in both the processes and it depends on prealuminizing diffusion and the subsequent aluminizing treatment employed.
Aluminide
High-Temperature Corrosion
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To shield TiAl alloy from hot corrosion attack, a compact protective coating was fabricated by the combination of aluminizing, anodization and pre-oxidation. The hot corrosion behavior of the coated-TiAl specimen was investigated in the mixture salt consisting of 75 wt.% Na2SO4 and 25 wt.% NaCl at 700 °C. Results indicated that the anodization and pre-oxidation were beneficial to the generation of Al2O3 layer, which could act as a diffusion barrier to prevent the molten salts and oxygen from diffusing into the alloy during exposure to a hot corrosion environment while the aluminizing coating could provide sufficient aluminum source to support the continuous formation of Al2O3 layer. Moreover, the internal stress of the coating was reduced due to the formation of a gradient coating consisting of TiAl3 and TiAl2.
Anodizing
Diffusion barrier
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Oxidation resistance of hot dipping aluminized steel is very good. In order to improve the property of 1Cr18N9Ti and 1Cr13 stainless steel used at high temperature, tests of hot dip aluminizing and oxidation resistance were done on them.The results of high temperature oxidation tests show that the HDA coating obviously improves the oxidation resistance of 1Cr18Ni9Ti steel and 1Cr13 steel. The improvement mainly depends on the change of alloy layer during oxidation. Oxidized at 900℃ for 500h, the HDA 1Cr18N9Ti steel has formed a compact α-Al 2O 3 oxide film and a single β-NiAl phase layer, and the HDA 1Cr13 steel has formed a compact Al 2O 3 oxide film and Cr 2O 3 oxidate. The research shows that the effect of Cr and Ni on oxidation resistance of aluminized stainless steel is most significant.
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Aluminide
Nickel aluminide
Plating (geology)
Nickel alloy
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The aluminizing treatment on the surface of commercial pure copper with addition of rare earth compoundCeCl3 was carried out. The following internal oxidation of the aluminized copper was also carried out in thecommercial nitrogen gas medium. The influences of the aluminizing and internal oxidization processing time on thethickness, hardness profile and microstructure were investigated. Results show that the addition of rare earth oxideCeCl3 has great accelerating effect on the aluminizing and internal oxidation processing. The hardness of the surfaceAl2O3 dispersion hardened copper composite layer by means of internal oxidation with addition of rare earthcompound is higher than that of the no rare earth compound addition.
Internal oxidation
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In order to improve the corrosion resistance of the sputtered NiCrAlY and provide the basis for the application of the coating,a nanocrystalline Ni-30Cr-8Al-0.5Y coating was deposited on a Ni-based superalloy by magnetron sputtering.Post-aluminizing was performed on the sputtered coating to further upgrade its corrosion resistance.The corrosion behavior of the sputtered coatings without and with post aluminizing by NaCl deposit in oxygen containing water vapor at 700℃ had been investigated using TGA,SEM/EDS,XRD and EPMA,respectively.The results indicated that the sputtered coating suffers from serious corrosion due to the reaction of Cr and Cr2O3 with NaCl,resulting in spallation of oxide scales and thus degradation of the coating.On the contrary,a single Al2O3 scale forms on the post-aluminizing sputtered coating surface,which exhibits high chemical stability in corrosive environment and provides protection for the sputtered coating.
Nanocrystalline material
Chromia
High-Temperature Corrosion
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Ion plating
Plating (geology)
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The corrosion resistance of hot-dip aluminizing coating doped with cerium and magnesium was evaluated by conducting corrosion tests in various fluids. The microstructure , elemental composition and phase composition of the corroded aluminizing coating were analyzed using a scanning electron microscope, an energy dispersive spectrometer, and an X-ray diffractometer. Results showed that adding 0. 5 % cerium helped to improve the corrosion resistance of the aluminizing coatingin strong aqueous acids, saline water, and tap water. The additionof 0.5% cerium and 1.0% Magnesium further contributed to improve the corrosion resistance of the aluminizing coating in diifferent fluids. However, the addition of cerium and magnesium had no significant effect on the corrosion resistance of the alumi-nizing coating in strong alkaline solution.
Diffractometer
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Pack chromizing and aluminizing has been widely used for many years to improve hot temperature oxidation and corrosion resistance of metals. The coating process involves packing the steel in a powder mixture which contain aluminum and chromium source, and inert filler (usually alumina), and halide activator NH4Cl. Al and Cr were deposited onto carbon steel by pack cementation process using elemental Al and Cr powder as Al and Cr source, whereas NiCo alloys codeposited by electrodeposition. The position of Al and Cr could be under or over Ni-Co alloys deposited. Pack cementation was heated on dry inert gas at temperature 800 °C about 5 hours and 20 minute for Cr and Al respectively. Al and Cr was successfully deposited. Laying down effect of Al and Cr onto carbon steel whether up and down toward NiCo alloys coating have affected to oxidation resistance. The pack aluminizing as top layer given best resitance to restrain excessive oxide scale, in contrast pack chromizing reveal bad oxidation resistance, moreover occured spallation on layer.
Cementation (geology)
Inert gas
Inert
Carbon steel
Carbon fibers
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