Papers by Keyword: Aluminizing

Abstract: The influence of the chemical composition of aluminide coatings of the Fe-Cr-Al system on their heat resistance at 1100 °C was investigated. It is shown that the lowest oxidation rate is possessed by the coating obtained by aluminizing the Cr15Al5 alloy in the silumin melt, for which the depth of corrosion penetration after 500 h at 1100 °C did not exceed 2.5 μm. The depth of corrosion penetration after 500 h at 1100 °C in coatings with a higher chromium content (23 at.%) reaches 8.9 μm. A decrease in the content of chromium (up to 5 at.%) or aluminum (up to 10 at.%) in the surface layer is accompanied by a critical increase in the corrosion rate. The longest time of retention of heat-resistant properties at 1100 °C is possessed by the coating obtained by aluminizing the Cr23Al5 alloy in an aluminum melt.

Abstract: The effect of thermal action at 1100 °C on the kinetics of phase transformations in the coating, obtained by hot-dip aluminizing of 12Cr18Ni10Ti steel, is studied. It was shown that, after 500 h of exposure, the chemical composition is leveled over the entire volume of the sample. Moreover, the predicted retention time of the heat-resistant properties of the coating at 1100 °C is about 2000 h.

Abstract: The influence of thermal action at 1150 °C on the kinetics of phase transformations in a layered coating FeAl (Cr,Si) / Fe₃Al (Cr,Si) / Fe (Al,Cr,Si), obtained using a technology involving aluminizing of an Cr15Al5 alloy by hot dipping in silumin melt AK12M2 and heat treatment. It was shown that after 100 hours of exposure, the visually distinguishable boundary between the coating and the alloy disappears. The aluminum content in the Cr15Al5 alloy increased to 17 at. %, silicon up to 3 at. %, and chromium is reduced to 14 at. %. The microhardness of the alloy increases from 1.6 to 2.4 GPa and survivability at a test temperature of 1150 °C increases from 120 to at least 920 hours.

Abstract: Anodic current-supplying pins (ACP) made of low-carbon steel corrode intensively due to the sulfur contamination of the carbon-based Soderberg anode and iron sulfides formation in the present aluminium production technology. The aluminide coatings produced by the liquid-phase method followed by the fluoride flux treatment of the steel samples were applied for the ACP protection. The protective layer based on α-Al₂O₃ and FeAl₂O₄ was formed on the steel surface in the course of the test run in the industrial Soderberg anode during the aluminium electrolysis. The aluminized ACP wear rates calculated by the linear extrapolation of data obtained during 150 days workout were 4.0 and 5.4 cm/year for the ACP with the aluminide coating and without it, respectively. The current load on the ACP remained almost the same for the aluminized and original uncoated samples with the exception of the initial “heating” period (400-600°C).

Abstract: The pack-cementation is one of economical, efficient coating processes for Fe-base alloys. It can provide good protection against high-temperature oxidation and corrosion. In this study, the high-temperature corrosion behavior of the aluminized diffusion-coating on low-carbon T20 steel (Fe-2.0Cr-0.5Mo-0.8Mn-0.3S in at.%) was studied at 800 °C in N₂/H₂O/H₂S-mixed gas. The aluminized coating consisted of Fe₃Al. The aluminized T20 steel after corrosion at 800 °C for 10~100h in N₂/H₂O/H₂S-mixed gases, the scale formed on the Fe₃Al coating consisted primarily of α-Al₂O₃, Al₂S₃, FeAl₂O₄ and FeO, with relatively slow scaling rates. The Fe₃Al intermetallics has reasonable corrosion-and oxidation-resistance, because it can form a protective alumina scale. Without the aluminized diffusion-coating, T20 steel corroded fast with serious scale failure. At the surface, coarse FeS grains with cracks formed. Since FeS has a very high concentration of cation vacancies, it grew fast through the outward diffusion of Fe²⁺ ions.

Abstract: The paper presents results of microstructural analysis of Hf-modified aluminide coatings. The coating was obtained using chemical vapour deposition (CVD) method at 1040°C using BPX-Pro 325 S equipment (Iond Bond). The deposition process time was 960 mintutes. The IN-718, IN-100 as well as CMSX-4 single-crystal nickel superalloys were the substrate material. The observation of coating was carried out using scanning electron microscopy. Chemical composition was analyzed using EDS method. The results showed that hafnium accumulates mainly on diffusion/additive layer interface and forms a „chain” of small precipitations. Hafnium was found in the additive NiAl layer of aluminide coating deposited on IN-100 superalloy. Its amount did not exceed 0.3 at %.

Abstract: A multilayer intermetallic coating on low-carbon steel was obtained during aluminum electrodeposition in NaF-KF-AlF₃ melt at 920 °C. The current density effect on morphology and intermetallic layer composition was investigated. Electrolytically aluminized steel samples represented a good oxidation resistance at 900 °C.

Abstract: Steel sheet has one major drawback, it is attacked by moisture at low temperatures and oxygen at high temperatures. Fortunately, coatings can provide protection to steel sheet from corrosion. Aluminum and aluminum zinc coatings can be applied by different methods. These are chemical vapor deposition coating (CVD), slurry coating, vacuum coating, spray coating, cladding, electroplating, electrophoresis, diffusion coatings, cementation, calorizing and hot dipping. This paper aims at providing a survey of these processes.

Abstract: A metallurgical method for preparing oxide nano-rod array structure was developed with internal oxidation of Ni(Al) solid solution obtained by aluminizing Ni with a pack cementation technique. The present method was applied in order to fabricate nano-rod array on the micro-channel surface of microreactor. A micro-channel with 1 mm in depth, 1mm in width and 10 mm in length was fabricated on the Ni disk by an electric discharge machining and electropolishing. The Ni disk with a micro-channel was annealed at 1300°C for 12 h in vacuum. The sample was aluminized by a pack cementation using pack powder mixture consisting of 10 mass% of Ni3Al, 88 mass% of Al2O3 and 2 mass% of NaCl at 1100°C for 12 h in a flow of argon gas. The sample was oxidized from 1000 to 1200°C for 6 h with the Co/CoO buffer. Ni matrix in internally oxidized zone was removed by electropolishing to expose nano-rods. Al2O3 nano-rod array located on the micro-channel surface was successfully fabricated with the proposed technique. Diameter and height of nano-rods were ranged from 100 to 300 nm and from 1.5 to 3 µm, respectively.

Abstract: In this paper, the effects of aluminizing agent composition, filler particle size, process parameters and adding impinging particle into aluminizing agent on the thickness of aluminizing layer were investigated. The mechanism of the significant reduction in aluminizing temperature using aluminizing agent was analyzed. The results indicate that the aluminizing temperature can be reduced to 500°C through mechanical energy aided aluminizing. The mechanical energy aids to improve the surface adhesion probability of Al powders on the specimen surface, increases the chemical activity and adhesion strength of Al powders, thus the aluminizing temperature is greatly reduced.