Production of Aluminide Layers on AISI 304 Stainless Steel at Low Temperatures Using the Slurry Process (original) (raw)
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Intermetallics, 2020
In the present work, a novel technique has been introduced to obtain an aluminide coating by casting process and subsequent heat treatment. To do so, the aluminum sheet was placed at the bottom of a copper mold, then HH309 SS melt was poured into the mold. This technique was named Cast-Aluminizing (CA). The CA samples were heat-treated at the temperature range of 900-1050 � C for 0.5-5 h. The FE-SEM, XRD, and EDS were utilized to characterize the microstructure, phase analysis and chemical composition of cast-aluminized samples, respectively. Results showed that (Fe,Cr,Ni)Al 3 and (Fe,Cr,Ni) 2 Al 5 layers were formed at the Al/HH309 interface. FE-SEM analysis demonstrated a multi-layer aluminide coating on the heat-treated specimens. This coating consisted of (Fe,Cr,Ni) 2 Al 5 þ(Fe,Cr,Ni)Al 2 , (Fe,Cr,Ni)Al and α-Fe,Cr,Ni(Al) sub-layers. The growth kinetics investigation showed that the thickness of layers increased with the increase of the annealing temperature and time. The growth rate of layers obeyed a parabolic law. The activation energies for the growth of (Fe,Cr, Ni) 2 Al 5 þ(Fe,Cr,Ni)Al 2 , (Fe,Cr,Ni)Al and α-Fe,Cr,Ni(Al) layers were about 203, 250 and 247 kJ/mol, respectively. Microhardness measurements revealed that (Fe,Cr,Ni) 2 Al 5 þ(Fe,Cr,Ni)Al 2 , (Fe,Cr,Ni)Al and α-Fe,Cr,Ni(Al) layers had a hardness of about 820-1040, 580-710 and 380-470 HV, respectively. The resistance to oxidation of castaluminized and heat-treated (CA þ HT) samples in the air at 1000 � C was studied. The CA þ HT samples exhibited higher oxidation resistance than uncoated samples due to the formation of a protective Al 2 O 3 layer on the surface.
Effect of Low-Temperature Aluminizing on 904L Stainless Steel
2021
Intermetallic materials exhibit desirable properties for many applications. They can be produced by traditional production techniques such as casting or powder metallurgy. In addition, they can be manufactured using some coatings techniques. Pack cementation technique is a very cheap, fast and simple operation to produce an intermetallic layer. 904L super austenitic stainless steel composed of high amounts Fe, Ni and Cr. It can be used in pulp and paper processing, some acid processing plants, cooling devices or oil refinery material. Its hardness is not high, and its usage temperature is low (<400 °C). To enhance these properties, aluminizing technique can be used. In the current study, 904 L super austenitic stainless steel was used as substrate material for the pack aluminizing process. The aluminizing process was applied at 675 °C for 2 and 4 h. After the aluminizing process, an aluminide layer formed on the 904L steel. The obtained aluminide layer thickness is about 19.2 and...
Iron Aluminide Coating on Steel Surface by Mechanical Alloying at Elevated Temperature
Transactions of the Materials Research Society of Japan, 2009
A new type of iron aluminide coating on a steel substrate by mechanical alloying (MA) with Al-Fe powders was examined. Precoating was carried out by a high-energy planetary MA with Al-Fe powder at room temperature, followed by low-energy MA at an elevated temperature. In MA at 500 °C, the precoating layer becomes soft and the interdiffusion between Al and Fe is enhanced, resulting in the formation of a homogenous iron aluminide coating layer on a steel substrate. By MA at 500 ºC for 4 h, a Fe 2 Al 5 coating layer is formed for Al-25 at%Fe powder, and a FeAl coating layer with a small amount of Fe 2 Al 5 is formed for Al-50 at%Fe powder. The Fe-Al solid solution is achieved near the steel substrate/coating layer interface in a substrate, resulting in good bonding between the substrate and the coating layer. The Al-50 at%Fe coating layer has a hardness of 7.8 GPa and high fracture toughness.
Aluminization of high purity iron and stainless steel by powder liquid coating
Acta Materialia, 2004
Powder liquid coating is investigated metallographically as an aluminization technique for high-purity iron [Acta Mater., in press] and stainless steel. In this process, Fe 2 Al 5 forms initially during heat treatment, with c axis preferentially aligned with the sample normal. In Fe-18mass%Cr alloy, Cr exhibits almost the same concentration profile as Fe except for the temporary formation of a Cr 5 Al 8 network in the early stage of heat treatment. Fe-25Cr-18Ni alloy forms a thinner aluminized layer compared to the other substrates, and contains an Al-Ni-rich layer and spherical precipitates (ordered B2). The diffusion of Al and Ni in the system (B2/bcc/fcc) is simulated using a new formulation of the diffusion equation for the ternary Fe-Al-Ni system taking the concentration-dependent interdiffusion coefficient into account. The bcc layer is found to be predominantly in a steady state due to the large interdiffusion coefficients, and characteristic uphill diffusion of Al in the B2 layer is attributed to the existence of Ni.
Deposition of Aluminide Coatings onto AISI 304L Steel for High Temperature Applications
Materials
The nickel aluminides are commonly employed as a bond coat material in thermal barrier coating systems for the components of aeroengines operated at very high temperatures. However, their lifetime is limited due to several factors, such as outward diffusion of substrate elements, surface roughness at high temperatures, morphological changes of the oxide layer, etc. For this reason, inter-diffusion migrations were studied in the presence and absence of nickel coating. In addition, a hot corrosion study was also carried out. Thus, on one set of substrates, nickel electrodeposition was carried out, followed by a high activity pack aluminizing process, while another set of substrates were directly aluminized. The microstructural, mechanical, and oxidation properties were examined using different characterization techniques, such as SEM-EDS, optical microscopy, XRD, optical emission spectroscopy, surface roughness (Ra), and adhesion tests. In addition, the variable oxidation temperatures...
Aluminium based protective coatings produced on AISI 304 stainless steel
Le Journal de Physique IV, 1993
The diffision of Aluminium is one of the most promising methods to build superficial coatings for stainless steel protection. Heat treatments at 800 OC performed on rods of AISI 304 steel, Aluminium coated by means of electrodeposition, displayed the possibility of forming intermetallic compounds. Depending on the duration of the heat treatment and on the cooling kinetics, these compounds can be continuous. At high cooling kinetics (water cooling) a two-phase structure composed of y' (Ni3Al) and y (substitutional solid solution) is obtained. At slow cooling rates (in furnace), a substitutional solid solution and some precipitates of y' (Ni3Al) and p (NiAl) can be observed. At intermediate cooling rates (oil cooling and air cooling), only the substitutional solution and the y' phase are present. Using furnace cooling from 800 OC until 500 OC, permanence at this temperature for I92 h and cooling furnace, the two-phase structure obtained is composed of the substitutional solid solution and the j 3 (NiAl) phase. The existence of these phases and their composition have been reported by X-ray diffraction patterns and microanalysis. The possibility of forming a natural composite, constituted by a hard phase of aluminides diffised in a substitutional solid solution, has an important consequence on the mechanical and protection properties of these coatings. Moreover, the diffusion of Al improves the adhesion of coatings.
Resistance of Aluminide Coatings on Austenitic Stainless Steel in a Nitriding Atmosphere
Materials, 2021
A new slurry cementation method was used to produce silicide-aluminide protective coatings on austenitic stainless steel 1.4541. The slurry cementation processes were carried out at temperatures of 800 and 1000 °C for 2 h with and without an additional oxidation process at a temperature of 1000 °C for 5 min. The microstructure and thickness of the coatings were studied by scanning electron microscopy (SEM). The intention was to produce coatings that would increase the heat resistance of the steel in a nitriding atmosphere. For this reason, the produced coatings were subjected to gas nitriding at a temperature of 550–570 °C in an atmosphere containing from 40 to 60% of ammonia. The nitriding was carried out using four time steps: 16, 51, 124, and 200 h, and microstructural observations using SEM were performed after each step. Analysis of the chemical composition of the aluminide coatings and reference sample was performed using wavelength (WDS) and energy (EDS) dispersive X-ray micr...
2011
Oxidation resistance of chromium steels is due to the formation of Cr 2 O 3 on the surface. However, this surface layer destabilizes above 1,000°C and does not protect the metal. In this study, three types of coatings were applied to AISI 304 stainless steel (SS), and the microstructure and oxidation resistance of the coatings were investigated. Aluminum coating, silicon coating, and the codeposition of Al and Si were deposited on an SS substrate by the pack cementation method. The microstructure of the samples was then examined by SEM and EDS, and phases were identified by XRD. The oxidation resistance of these samples was studied in air at 1,050°C. The results showed that the best resistance to oxidation was obtained, in order, from the codeposition of Al-Si, Al coating, and Si coating.
Materials Science : An Indian Journal, 2010
316L stainless steel; Aluminizing; Al-Si alloys; Intermetallic layer; Microhardness. KEYWORDS ABSTRACT 316L stainless steel was coated by hot-dipping into commercially pure Al and two Al-Si alloys of 7%Si and 11.5% Si contents at dipping time varying from 1 to 60 min and temperatures ranging from 750 to 900ºC. Moreover, 5%Fe was added to each bath at 900C. Microstructure observation, morphology of the alloy layer, element distribution, chemical composition and microhardness determination were performed by optical microscopy, scanning electron microscope (SEM) with an energy dispersive X-ray facility (EDX), and microhardness tester. The thickness of the intermetallic layer formed increases with increasing both the bath temperature and dipping time. Based on the experimental data, it is found that the largest and most uniform layer thickness was obtained at 800ºC and time 20 min in pure Al molten bath, and this is also the case when aluminizing in Al-11.5%Si molten bath, but when using Al-7%Si molten bath, the optimum dipping temperature was about 750C also at time 20 min. The existence of Si reduces the intermetallic layer thickness and increases its microhardness. The addition of 5%Fe to the melt increases the layer thickness.
Aluminide Protective Coatings Obtained by Slurry Method
The slurry aluminide coatings were deposited on the three kind of substrates: high– temperature creep resistant cast steel, titanium alloy and nickel alloy. The applied slurry was an active mixture containing aluminium and silicon powders, an activator and an inorganic binder. The coatings were obtained by annealing in air atmosphere. The structure of these coatings was dual-zone and depended on type of the substrate and technological parameters of producing.