Effect of Si addition on the microstructure and oxidation behaviour of formed aluminide coating on HH309 steel by cast-aluminizing (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.
Microstructure studies of an aluminide coating on 9Cr-1Mo steel during high temperature oxidation
Surface and Coatings Technology, 2006
9Cr-1Mo steel coated by hot-dipping into a molten mixture with 7wt.%Si/93wt.%Al was oxidized at 750, 850, and 950°C in static air. The oxidation kinetics followed a parabolic rate law at all temperatures. Intermetallic iron-aluminum compounds FeAl 3 , Fe 2 Al 5 , and FeAl 2 initially formed on the steel substrate at elevated temperature. At 850°C the Fe x Al y layer thickness increased rapidly during the first 20 min and Fe 2 Al 5 mixed with FeAl 2 became the main phases in the aluminide layer. Some cracks propagated through the Fe x Al y brittle FeAl 2 and Fe 2 Al 5 layers. After 24 h oxidation at 850°C, all FeAl 2 +Fe 2 Al 5 transformed to FeAl, while FeAl 2 +Fe 2 Al 5 still existed at 750°C after 56 h exposure. The Kirkendall effect is a plausible mechanism for the voids observed at the interface between the aluminide layer and the steel substrate.
Materials Research Express, 2019
An ASTM A29 steel was coated with aluminide by dipping in a molten Al bath at 700°C for 16 s. The resistance of ASTM A29 steel to high-temperature oxidation drastically decreased upon oxidation at 850°C for 12 h, whereas the oxidation resistance of the aluminised steel subjected to hot dipping was higher (by 25-fold). The external part of the aluminide layer, which consists of Fe2Al5, FeAl2, and FeAl(Cr,Si) phases scattered in the Fe2Al5 phase, was formed through the outward diffusion of Al and inward diffusion of Fe. The Fe2Al5 phase played an important role as a reservoir of Al atoms that form the alumina (Al2O3) scale, while Cr and Fe from the FeAl(Cr,Si) particles and accelerated the conversion of the metastable -Al2O3 phase to a stable -Al2O3 phase. Consequently, the parabolic rate constants of aluminised steel decreased with extended oxidation time.
Journal of Nuclear Materials, 1996
In a previous work, it has been shown that lower aluminium content aluminide, having the same permeation rate reduction as the higher aluminium content, exhibited a lower hardness and greater ductility and therefore greater crack resistance than the higher aluminium content. In this work we combine this characteristic with a post-oxidation to obtain a further deuterium permeation reduction. The post-oxidation was performed in air at 1023 K for 15 h and at 1223 K for 10 h and 1 h. The maximum deuterium permeation rate reduction obtained is very moderate (maximum of a factor 500 for 1 h at 1223 K) as compared to that of the non-oxidised aluminide specimen (two orders of magnitude) and is constant in the temperature range studied (573-800 K). This method has the technological appeal of using air rather than the controlled environment used by other authors.
The structure of aluminide coatings on alloy steels in the area of the welded joints
INŻYNIERIA MATERIAŁOWA, 2017
Preparation of aluminide coatings is used to increase the heat resistance. The coating must be frequently applied to details that were previously welded. The description of the structure of the coating in the area of the welded joint can be important when choosing the proper welding techniques. Butt joints were made using tungsten inert gas, arc welding-the method 141. The main differences between the joints are a kind of parent material and production technology (welding with or without a filler material). Parent materials for making the joins are 1.4749 (X18CrN28) and 1.4404 (X2CrNiMo17-12-2) steels. On prepared samples with joints the silicon-aluminide coating by the slurry method were produced. Samples covered by the slurry were annealed in a furnace with a protective atmosphere of argon at two temperatures 800 and 1000°C for 2 hours. To characterize the structure of the coatings electron microscopy, SEM and EDS X-ray microanalysis were used. It was found that the coatings were formed on the whole test surface. There are strong similarities between the structure of coatings produced in a given temperature despite the use of different substrates and various welded joints. Generally, the coatings produced at a temperature of 800°C are characterized by a three-layer structure, while those at 1000°C have two layers. The thickness of the coating produced at 800°C is from a range of 40 to 65 μm depending on the substrate. The thickness of coatings annealed at 1000°C is in the range of 100 to 200 μm. It is noted that the thickness of the coatings on the parent material is in any case higher than on the weld.
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...
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...
Heat treatment was introduced onto the aluminum coated low carbon steel to promote the formation of thin layer of oxide for enhancement of oxidation protection of steel. This process has transformed the existing intermetallic layer formed during hot dip aluminizing process. Experiment was conducted on the low carbon steel substrates with 10mm x 10mm x 2mm dimension. Hot dip aluminizing of low carbon steel was carried out at 750 ºC dipping temperature in a molten pure aluminum for 5 minutes. Aluminized samples were heat treated at 600 ºC, 700 ºC, 800 ºC, and 900 ºC for 1 hour. X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and EDAX were used in investigation. From the observation, it showed the intermetallic thickness increased with the increase in temperature. The result of EDAX analysis revealed the existence of oxide phase and the intermetallics. The XRD identified the intermetallics as Fe2Al5 and FeAl3. ABSTRAK Rawatan haba telah diperkenalkan ke atas aluminium bersalut keluli berkarbon rendah menggalakkan pembentukan lapisan nipis oksida untuk peningkatanperlindungan pengoksidaan keluli. Pembinaan ini telah mengubah lapisan antaralogam sedia ada membentuk semasa pencicah pedas pengaluminiuman proses.Eksperimen dijalankan di substrat keluli berkarbon rendah dengan 10mm x 10mmdimensi x 2mm. Pengaluminiuman pencicah pedas keluli berkarbon rendah telah dijalankan di 750 suhu pencelupan ºC di satu aluminium tulen lebur selama 5 minit.Contoh-contoh Aluminized ialah haba merawat di 600 ºC, 700 ºC, 800 ºC , dan 900 ºC untuk 1 jam. Belauan Sinar-x (XRD), Scanning Electron Microscope (SEM) and EDAXtelah digunakan dalam penyiasatan. Dari pemerhatian, ia menunjukkan ketebalan antara logam menambah dengan kenaikan itu dalam suhu. Keputusan analisis EDAXmendedahkan kewujudan fasa oksida dan intermetallics. XRD mengenal pastiintermetallics sebagai Fe2Al5 and FeAl3.
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...
High Temperature Oxidation Performance of Aluminide Coatings
2003
In order to determine the potential benefits and limitations of aluminide coatings, coatings made by chemical vapor deposition (CVD) on Fe-and Ni-base alloy substrates are being evaluated in various hightemperature environments. Testing of coatings on representative ferritic (Fe-9Cr-1Mo) and austenitic (type 304L stainless steel) alloys has found that high frequency thermal cycling (1h cycle time) can significantly degrade the coating. Based on comparison with similar specimens with no thermal cycling or a longer cycle time (100h), this degradation was not due to Al loss from the coating but most likely because of the thermal expansion mismatch between the coating and the substrate. Several coated Ni-base alloys were tested in a high pressure (20atm) steam-CO 2 environment for the ZEST (zero-emission steam turbine) program. Coated specimens showed less mass loss than the uncoated specimens after 1000h at 900°C and preliminary characterization examined the post-test coating structure and extent of attack.