Aluminization of high purity iron and stainless steel by powder liquid coating (original) (raw)
Related papers
Aluminization of high purity iron by powder liquid coating
Acta Materialia, 2004
A new powder liquid coating method is proposed for the aluminization of Fe. Mixed powder slurries of Al + Ti or Al + Al 2 O 3 are pasted onto Fe specimens, and the specimens are then dried and heated in a vacuum. Unlike hot dipping or powder pack cementation, this technique can be used to aluminize specimens selectively without the need for special equipment or halides. The amount of Al adhering to the substrate is determined by the Al-Ti reaction or coalescence of molten Al in Al 2 O 3 powder during heat treatment. The Al concentration profile of the modified layer can be controlled by adjusting the powder mixing ratio or heat treatment conditions. The properties of the modified layer are analyzed using a new formulation, where the diffusion equation is treated numerically with consideration of the concentration dependence of the interdiffusion coefficient. The calculated profiles are stable and in good agreement with the experimental data.
Mechanical Alloying-assisted Coating of Fe–Al Powders on Steel Substrate
Makara Journal of Technology, 2020
The coating layer of Fe-Al powders on the steel substrate was prepared by mechanical alloying at room temperature. Fe, Al, and the steel substrates were milled with high-energy ball milling for 32 h with a ball-to-powder ratio of 8 in an argon atmosphere to prevent oxidation during milling. Although mechanical alloying was performed for 32 h, no new phases were observed after mechanical alloying, as analyzed by X-ray diffraction. However, the crystallite size of the milled powders for 32 h decreased by factor two compared with the initial powders. Scanning electron micrographs showed that the coating layers formed >8 h after mechanical alloying. The intermetallic Fe 3 Al formed after the substrate was annealed at 500 ℃.
Journal of Materials Engineering and Performance, 2020
Intermetallic compounds, such as iron aluminides exhibit excellent oxidation and corrosion resistance, as well as metallurgical bonding with excellent adhesion to the substrate. In this work, aluminizing treatments were carried out using the dipping into slurry process to produce iron aluminide coatings on stainless steel substrates. In this process, AISI 304 stainless steel samples were immersed in a slurry consisting of polyvinyl butyral, ethyl alcohol and a powder composed of Al, AlCl 3 and Al 2 O 3 , dried and then placed in sealed crucibles without further protection. These samples were treated at temperatures of 500 and 650°C for 2, 4, 6 and 8 h and then air-cooled. Flat and homogeneous layers were obtained over the substrate with increased thickness observed with increasing temperature and treatment time. Considering that the traditional treatments of aluminization by the pack process are carried out at temperatures close to 900°C and use larger amounts of material, the low temperature treatments used in this work offer potential cost savings.
Hot-Dip Aluminizing of Low Carbon Steel Using Al-7Si-2Cu Alloy Baths
Journal of Coatings, 2013
Hot-dip aluminizing of low carbon steel was done in molten Al-7Si-2Cu bath at 690°C for dipping time ranging from 300 to 2400 seconds. Characterization of the intermetallics layer was done by using scanning electron microscope with energy dispersive spectroscopy. Four intermetallic phases,τ5-Al7Fe2Si,θ-FeAl3,η-Fe2Al5, andτ1-Al2Fe3Si3, were identified in the reaction layer.τ5- Al7Fe2Si phase was observed adjacent to aluminum-silicon topcoat,θ-FeAl3betweenτ5andη-Fe2Al5,η-Fe2Al5adjacent to base material, andτ1-Al2Fe3Si3precipitates within Fe2Al5layer. The average thickness of Fe2Al5layer increased linearly with square root of dipping time, while for the rest of the layers such relationship was not observed. The tongue-like morphology of Fe2Al5layer was more pronounced at higher dipping time. Overall intermetallic layer thickness was following parabolic relationship with dipping time.
Formation Behavior of an Intermetallic Compound Layer during the Hot Dip Aluminizing of Cast Iron
ISIJ International, 2012
Hot dip aluminizing (HDA) is an effective way to improve the high temperature corrosion resistance and scaling resistance of ferrous materials. The formation of intermetallic compound layers between the two materials is a dominant factor in determining the properties of hot dip aluminized steel. The formation behavior of the intermetallic compound layer between a Si alloyed Al melt and cast iron has been investigated. The thickness of the intermetallic compound layer was significantly reduced as a result of the increased carbon content of the cast iron matrix. The thickness of the intermetallic compound layer formed in the Al-Si-Fe three-component alloy system remains constant in the early stage of the reaction, and it becomes increasingly rough with increased reaction time. The increased roughness could be attributed to the increased Fe concentration in the Al-Si melt near the cast iron surface, which is a result of the increased inter-diffusion of Al, Si and Fe atoms with increased reaction time by which the formation, melting and spallation of the intermetallic compound layer is enhanced.
Surface and Coatings Technology, 2013
A novel approach to apply slurry aluminides to produce a thermal barrier system based on an aluminum diffusion zone and an alumina foam layer in one step is being studied in the European FP7 project PARTICOAT. The results suggest possible coating and substrate combinations to decrease the degradation of slurry-produced aluminide coatings under high temperature exposure in heat exchangers, boilers or combustion chambers present in waste incineration and power plants. Spherical Al or Al-Si particles were deposited by air brush technique on austenitic (AISI347), ferritic (AISI446) and ferritic-martensitic (P91) steels. Isothermal exposure tests were performed at 600°C and 800°C for up to 1000 h to study the microstructural changes and the oxidation behavior in air. After manufacturing, the resulting diffusion coating consisted of different iron-aluminide phases with porous alumina foam on top. The diffusion layer on top of the ferritic steels contained cracks due to the large thermal expansion coefficient mismatch between the substrate and the bondcoat, but was homogenous and continuous on the austenitic alloy. These cracks are generally filled with aluminum oxide in pure oxidizing atmospheres and the recession of aluminum in the diffusion layer is lower for the austenitic than for the ferritic alloys. The advantage of using an Al-Si based compared to a pure Al-slurry is a significantly decreased aluminum interdiffusion into the ferritic steels which contain high amounts of chromium. The latter effect could be related to the formation of a Cr 3 Si layer, which acts as an aluminum diffusion barrier.
Effect of Heat Treatment of the Alumina Powder on the Microstructure and Properties of Coatings
MATEC Web of Conferences, 2015
The alumina powder was treated at a high temperature (1000°C). Dense (porosity of less than 2%), solid (1280 ± 30 HV0.3) and wear-resistant coatings based on heat-treated alumina powder were obtained by a multi-chamber detonation sprayer on the steel substrate. The microstructure, microhardness and the wear resistance of the alumina coatings were investigated.
Preparation and oxidation of aluminum powders with surface alumina replaced by iron coating
Journal of Energetic Materials
Aluminum powders are well known for excellent release of energy during oxidation upon heating. However, this release of energy becomes limited due to formation of dense oxide (Al 2 O 3) layer on powder surface. In this study, reactivity of aluminum particles was improved by replacing oxide layer with metallic shell of iron using electroless plating technique. Three different bath compositions were selected for deposition of iron on aluminum particles. The surface morphology of prepared Al/ Fe core-shell composite powder was characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Further, iron content in the composite powder was measured quantitatively using helium gas pycnometer while elemental analysis was performed by X-ray diffraction (XRD). Finally, thermo-physical behavior of the composite powder was investigated using simultaneous thermogravimetry-differential scanning calorimetry (TG-DSC). The results showed that the synthesized Al/Fe core-shell composite powder exhibits higher energy release in comparison to the uncoated aluminum powder upon heating in air (up to 1180 °C). The powder with the densest iron coating released the highest energy.
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.
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.