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Ductile iron containing Si and Mo (SiMo) is a common alloy that has been used for exhaust car manifolds due to the need for high thermal cycling and being in an oxidizing environment. Al alloying has been shown in previous studies to reduce surface degradation during high temperature exposure of SiMo ductile iron. However, it has been shown to decrease the ductility and increase cracking during thermal cycling due to graphite shape degradation. To optimize composition and casting technology of Al-alloyed SiMo ductile iron, experimental castings containing 0.0% Al (base), 1.8% Al, and 3% Al were produced using a special melting procedure and tested at high temperature. Through experimental results and analysis, it was determined that the optimal Al alloying was dependent on a balance of oxidation and thermomechanical conditions. [ABSTRACT FROM AUTHOR]

Highlights • Thin FeCrAl coatings with Mo buffer layer on Zry-4 substrate can tolerate 1200 °C steam environment. • A systematic study of the oxidation behavior of FeCrAl-Mo bi-layer coatings is presented. • The migration of FeCrAl-Mo interface and voids formation mechanisms are consistent with the Kirkendall effect. Abstract FeCrAl alloys have exhibited excellent oxidation resistance in high temperature steam environment. However, over the past few years, thin film FeCrAl on zircaloy substrate can only tolerate up to 1000 °C steam because of the fast diffusion between zirconium and iron. In this study, we introduce Mo as a buffer layer and significantly reduced the inter-diffusion of zirconium and iron. The 7-micron thick FeCrAl coatings have shown excellent oxidation resistance up to 1200 °C, which is the highest temperature of thin FeCrAl coatings reported in literature. A systematic study of the oxidation behavior of FeCrAl coatings at 1000, 1100, 1200 °C is presented in this paper. [ABSTRACT FROM AUTHOR]

Ibuprofen (IBP) is one of the most known non-steroidal anti-inflammatory drugs. Due to the high consumption and the several ways of discharge, both the aquifer and soil matrix were contaminated by IBP. This study examined the degradation of the IBP in a soil matrix over Fe/Al oxidation electrodes in an electrokinetic system with processing fluids of sodium dodecylsulfate (SDS). The preparation of the Fe/Al oxidation electrode was carried out at a calcination temperature of 500, 550, and 600 °C, which accounted for Fe 3+ coating rate of 3.89 ± 0.03%, 4.62 ± 0.04%, and 4.72 ± 0.04%, respectively. Results indicated the generation of hydroxyl radical was proportional to the coating rate of Fe 3+ on the electrode. A 200 mg kg −1 of IBP-spiked soil sample was conducted in an electrokinetic system under a potential gradient of 2 V cm −1 . The experimental parameters included electrode area of 11–33 cm 2 and treatment time of 5–9 days. The remediation efficiency of IBP in the EK systems coupled with Fe/Al oxidation electrode was 70.1–94.6%, which was highly dependent on H 2 O 2 addition, electrode area, and treatment time. Both addition of H 2 O 2 and prolonging treatment time significantly enhanced the degradation of IBP. Whereas increasing electrode area was only favorable for removal mechanism of IBP. Five reaction mechanisms were clearly provided in this study. The aluminum plays an electron donner to trigger Fenton–like reaction continuously to produce hydroxyl radicals. This study confirmed that the electrokinetic process coupled with Fe/Al oxidation electrodes is a viable technique for the remediation of IBP-contaminated soil. Make good use of redox characteristic of aluminum to trigger the Fenton-like reaction in Fe 2+ -rich environment is a great success in this study. The use of Fe/Al electrodes effectively expands the application of electrochemical degradation in soil remediation. [ABSTRACT FROM AUTHOR]

In this study, the WC-FeAl composite was synthesized by mechanical milling and spark plasma sintering. The isothermal oxidation behaviour of the WC-FeAl composite was evaluated and compared with a commercial WC-Co composite at the temperature range of 700–900  ℃ . The results showed that the oxide layer formed in the WC-FeAl composite contained FeWO 4 , FeAlO 3 , and WO 3 phases at all tested temperatures. The XRD patterns indicated that the intensity of FeWO 4 and FeAlO 3 phases enhanced with increasing the oxidation temperature. The formation of these two phases was related to the diffusion of Fe and Al elements from the binder phase to the oxide layers. As a result of the presence of FeWO 4 and FeAlO 3 phases, more compact oxide scales were formed, and the volume of voids and cracks was decreased as compared to the WC-Co composite. The plot of specific mass variations as a function of time illustrated that the mass gain for WC-FeAl composite was almost half of WC-Co composite. [ABSTRACT FROM AUTHOR]

Formation of different iron aluminide (Fe-Al) layers during pack aluminizing of stainless steel 316, and subsequent heat treatments has been studied in detail. The single Fe 2 Al 5 layer formed during pack aluminization carried out in the temperature regime 450–650 °C is transformed into FeAl/Fe(Al) layers in the course of post aluminizing heat treatments conducted at higher temperatures. The iron aluminide layers were characterized using SEM, BSE, EDS and EBSD techniques. The precipitates of Cr 5 Al 8 are formed mainly in the Al-rich Fe 2 Al 5 layer, and they get completely dissolved in FeAl layer developed after heat treatment at 1050 °C. The concentration of porosities in the FeAl or Fe(Al) is reduced when the heat treatment temperature is lowered from 1050 to 900 °C. Controlled oxidation approach has been adopted to study the formation and phase transition (γ → θ → α) behavior of alumina (Al 2 O 3 ) scale in the temperature regime of 700–1050 °C. [ABSTRACT FROM AUTHOR]

The short-term isothermal oxidation behavior of B2 FeAl alloys doped with different reactive elements (REs) at 1273 K was investigated. All the RE-doped alloys showed retarded phase transformation from θ-to α-Al 2 O 3 as compared to the RE-free alloy. The Y- and La-doping even led to much lower transformation rate than the Hf-, Zr- and Ce-doping. The effect mechanism associated with RE ion size and valence on the phase transformation of alumina was discussed. The additions of RE ions which have large size and matched valence with Al ions could be anticipated to inhibit the transformation more effectively and the combined effects of retarding θ-α phase transformation, promoting α phase nucleation and suppressing Al outward diffusion produced by RE doping might provide FeAl with improved oxidation property. [ABSTRACT FROM AUTHOR]

Fe-Al alloys with different Al contents have been exposed to a microwave plasma activated CH 4 -H 2 gas mixture at 670 °C. An intermediate graphite layer formed on Fe-10Al substrate retarded diamond nucleation and deteriorated the interfacial adhesion, and severe metal dusting and carburization occurred. Diamond nucleation on Fe-20Al was enhanced by inhibited graphitization and cementite formation. Only Fe3AlCx-type precipitates were observed. On Fe-27Al and Fe-40Al alloys, graphitization and substrate carburization were completely prevented, producing enhanced nucleation and interfacial adhesion of diamond. The improved carburization resistance and diamond deposition with increasing Al contents is closely related to the formation of an alumina-rich layer on the alloy surface. [ABSTRACT FROM AUTHOR]

The cyclic oxidation of Fe–30Al– x Zr and Fe–25Al– x Zr ( x = 0.3–5.2 at.%) has been investigated at 900 °C and 1100 °C in laboratory air. Scales, oxide protrusions and structural changes were analysed by LOM, XRD, SEM and EDS. The oxidation rate increases with increasing Zr content as well as with increasing temperature. Spallation of thin scales formed at 900 °C on the Zr lean alloys is observed, while thicker scales formed on Zr-rich alloys or at 1100 °C show cracking but do not spall. At both temperatures the scales on all alloys consist of Al 2 O 3 , Fe 2 O 3 and ZrO 2 and oxide protrusions penetrate into the samples. These protrusions form by preferential oxidation of Zr rich phases. [ABSTRACT FROM AUTHOR]

This study investigated the effects of η-phase generation and the binder phase composition of iron aluminide (FeAl) on the mechanical properties of tungsten carbide–iron aluminide (WC–FeAl) composites. The η-phase was generated in the composites when the WC–FeAl powder was highly oxidized before sintering in a vacuum. The presence of the η-phase resulted in the degradation of mechanical properties such as transverse rupture strength (TRS) and indentation fracture toughness (IFT). In addition, FeAl composition varied mainly as a result of α-Al 2 O 3 formation. The iron-rich side of FeAl in binder phase improved the TRS and IFT. It was concluded that control of the η-phase generation and an appropriate FeAl composition are very important to maintain high TRS and IFT in the WC–FeAl system. [ABSTRACT FROM AUTHOR]

The oxidation behavior of binary Fe-Al alloys with an aluminum content between 58 and 64 at.% was studied by isothermal and cyclic oxidation experiments in a temperature range of 900-1000 °C. The parabolic rate constants were determined to be comparable to those of B2-ordered Fe-48Al. All investigated alloys exhibited a fine-scaled, lamellar microstructure (<300 nm lamellar spacing), which was a result of the eutectoid decomposition of the high-temperature phase FeAl into FeAl and FeAl. None of these two phases showed a preferential oxidation. At 900 °C θ-AlO formed, whereas at 1000 °C a transformation of the initially formed θ-AlO to the slower growing and passivating α-AlO was confirmed by grazing incidence X-ray diffraction measurements. [ABSTRACT FROM AUTHOR]

The oxidation behaviour of the FeCrAl alloy under normal operating conditions of a light water reactor is reported. In a comparative study, Zr-based and FeCrAl alloy samples were corroded in pressurized 360 °C water for up to 500 days or oxidized at 1200 °C for 3000 s in a steam environment. Compared to Zr-based alloys, the FeCrAl alloy showed extremely low weight change after both tests. The microstructure of the oxides formed on FeCrAl alloys was characterized by various analysing techniques. It was concluded that depending on the test conditions, mostly different oxide phases of α-Fe 2 O 3 and α-Al 2 O 3 were formed. [ABSTRACT FROM AUTHOR]

Iron aluminides with a protective alumina layer are considered candidate coating for test blanket modules of fusion reactor. In order to study the properties of plasma grown alumina in comparison with thermally grown alumina, oxidation studies on electro spark deposited (ESD) FeAl coating have been conducted. Glow discharge plasma oxidation has been adopted as plasma oxidation technique. Reduced activation 9Cr steel samples were coated with a coating of iron aluminide (FeAl) layer containing 45 at% Al. The ESD coated 9Cr steels were oxidized in air and plasma environments at 750 °C for 48 h. Resultant surfaces were studied using X-ray diffraction, electron probe microanalysis, SEM and electrochemical impedance spectroscopy (EIS) techniques. Although the presence of Al 2 O 3 was found on both thermally oxidized and plasma oxidized samples, the EIS studies clearly revealed improved dielectric properties of plasma grown Al 2 O 3 . The plasma grown oxide thin films seems a promising approach to apply alumina coatings with improved dielectric properties onto fusion reactor materials. [ABSTRACT FROM AUTHOR]

Selective oxidation experiments of four iron-aluminum model alloys, containing 1–8 wt.% Al, at temperatures up to 1285 °C have been performed. The total corrosion depth and composition of formed nitride and oxide phases have been analyzed by means of SEM/EDX and XRD. Experimental findings and the interplay between formed oxide and nitride phases were compared to theoretical predictions from numerical simulations and critically discussed. Conditions for the formation of a continuous oxide band underneath the sample surface will be highlighted, which represent a critical parameter window in industrial processes that may lead to severe mechanical damage during rolling. [ABSTRACT FROM AUTHOR]

Ferritic-structured Fe–Cr–Al alloys are being developed and show promise as oxidation resistant accident tolerant light water reactor fuel cladding. This study focuses on investigating the weldability and post-weld mechanical behavior of three model alloys in a range of Fe–(13–17.5)Cr–(3–4.4)Al (wt.%) with a minor addition of yttrium using modern laser-welding techniques. A detailed study on the mechanical performance of bead-on-plate welds using sub-sized, flat dog-bone tensile specimens and digital image correlation (DIC) has been carried out to determine the performance of welds as a function of alloy composition. Results indicated a reduction in the yield strength within the fusion zone compared to the base metal. Yield strength reduction was found to be primarily constrained to the fusion zone due to grain coarsening with a less severe reduction in the heat affected zone. For all proposed alloys, laser welding resulted in a defect free weld devoid of cracking or inclusions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fabrication of open-celled porous Fe(Al) foam near to 65% porosity. [•] The oxidation resistance of 10wt.% Al sample greatly improves compared to pure Fe. [•] The oxidation resistance performance promotes with increasing the milling time. [•] The increase of sintering temperature and soaked time improve oxidation resistance. [ABSTRACT FROM AUTHOR]

Porous Fe-Al intermetallics with different nominal compositions (from Fe-8 wt.% Al to Fe-50 wt.% Al) were fabricated by Fe and Al elemental powders through reaction synthesis. The effects of the Al content on the pore structure properties, and the comparison of pore structure stabilities at high-temperatures among the porous Fe-Al intermetallics and porous Ti, Ni, 316L stainless steel samples, were systematically studied. Results showed that the open porosity, maximum pore size, and permeability vary with the Al content. Porous Fe-(25-30 wt.%) Al intermetallics show good shape controllability and excellent pore structure stability at 1073 K in air, which suggests that these porous Fe-Al intermetallics could be used for filtration at high temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Iron aluminides containing 27, 33 and 39 at.% aluminum with low amounts (<0.5 at.%) of Zr, Nb, C and B have been investigated with respect to the interplay between microstructural evolution and oxidation behavior. Zirconium and Niobium have a low solubility in iron aluminides and form precipitates, e.g. Laves phases, carbides or borides. The isothermal oxidation behavior has been studied in laboratory air at 750, 900 and 1050 °C with respect to kinetic aspects and oxide layer growth. Mass change was recorded in intervals weighing the samples outside the furnace. The evolution of microstructure and layer growth has been analyzed utilizing SEM (EDX), EPMA, EBSD, XRD and OM. Generally, as expected, an outstanding oxidation resistance of all investigated alloys was observed due to the formation of Al2O3 scales with a very slow growth rate. However, in contrast to binary iron aluminides in the same composition range, the mass gain with time increases with increasing aluminum content. The findings are discussed in terms of scale properties and internal oxidation. [Copyright &y& Elsevier]

Several researchers have studied the transformation of metastable aluminas (γ- and θ-) to α-AlO but very little is known regarding alumina scales formed under water vapour and their transformation to α-AlO. Some results have indicated that water vapour increases the oxidation rate of alumina-scale forming coatings but others have found the opposite, that is, that under water vapour the oxidation rates decrease as either transition aluminas do not form or the transformation to α-AlO is accelerated. In addition, it was found that χ-AlO is the only oxide that forms at the initial stages of oxidation under 100 % steam on Fe-Al coatings at 650 °C. Under these conditions, this oxide is very protective, and slowly transforms onto α-AlO. A preliminary study of the transformation of χ- to α-AlO at 900 °C under laboratory air was carried out. χ-AlO was generated by a steam pre-treatment on slurry Fe aluminide coatings deposited on P92. [ABSTRACT FROM AUTHOR]

The possibility of a new technique for fabricating nanoparticles from thin films using selective oxidation in an atmosphere mixture of water vapor and hydrogen was investigated. Fe-5wt.%Al films were RF-sputtered and annealed in the atmosphere mixture at 900°C for up to 200 min, in order to oxidize aluminum selectively. Thermodynamics simulation showed that temperatures exceeding 800°C are necessary to prevent iron from being oxidized, as confirmed by the depth profile of XPS. As the annealing time increased, the morphology of the 200-nm Fe-Al films changed from the continuous to the discontinuous type; thus, particulate Fe-Al films formed after 100 min. The particulate 10- to 100-nm Fe-Al films showed super-paramagnetic behavior after the oxidation. Thus, a new technique for fabricating nanoparticles was successfully introduced using selective oxidation. [ABSTRACT FROM AUTHOR]

The development of the oxide scale on model Fe20Cr5Al-type alloys unmodified and containing implanted yttrium was studied in oxygen-dominated atmosphere at 1,100 °C for up to 1 h. A two-stage-oxidation exposure was applied with the use of O as a tracer. The choice of the exposure durations ensured the possibility to follow the consecutive stages of scale development. The oxidized samples were characterized using SEM (morphology); PLS (phase composition), and SIMS (elemental distributions). The obtained results are discussed in terms of the mechanism of the development of protective α-AlO scale and the effect of the additions on this process taking into account the necessity of distinguishing the mechanism and kinetics of the scale evolution. Similar scale evolution stages were found on both studied materials and in both cases the protective α-AlO scale developed rapidly, already after the exposure for 3 min. Implanted yttrium appeared to have a negligible effect on the evolution of the scale. It only slightly retarded the evolution which can be attributed rather to a kinetic effect than to mechanistic one. However, the mechanical failure of the scales via formation of cracks at the asperities of convolutions occurred on the yttrium-implanted alloy but not on the non-implanted one. [ABSTRACT FROM AUTHOR]

The tribological properties of Fe3Al-20 wt% Al2O3 composites, prepared by means of mechanical alloying and plasma-activated sintering, were investigated under air atmosphere against GCr15 bearing steels from room temperature to 500 °C. It was found that the friction coefficient of the composites (at 200 °C/350 °C) decreased with increasing temperature and the value was lower than that of Fe3Al alloys at the same temperature, and the friction coefficient increased again at 500 °C. Moreover, the wear rates of all the pins and discs were low at the medium/high temperatures. The dominant wear mechanism of the composites is microplowing and a little oxidation wear at room temperature. However, at elevated temperatures, oxidation wear and a little microplowing are found to be the main wear mechanism. There is also spalling induced by microfracture at 500 °C. The in situ Fe3Al-20 wt% Al2O3 composites have excellent wear resistance at a wide temperature range. [ABSTRACT FROM AUTHOR]

Abstract: The oxidation behaviour of two Fe3Al-based Fe–Al–Cr–Zr–C alloys has been evaluated between 900 and 1200°C. The alloys contained either (Fe,Al)2Zr Laves phase or ZrC carbide. The alloys were oxidised for up to 1000h in synthetic air using thermogravimetric analysis (TGA). Scales that formed on the surfaces of the sample as well as cross sections were analysed by light optical microscopy (LOM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectrometry (EDS). At 900°C parabolic growth and low weight gains for both tested alloys were observed. The scales are predominantly formed by Al2O3 with minor amounts of ZrO2. Some Fe2O3 was observed after oxidation at 900°C. At 1000°C oxidation ingresses into the samples along grain boundaries due to preferential oxidation of the Zr-rich precipitates, becoming more severe at higher temperatures. Ingress of oxidation into the sample is more pronounced for the alloy containing ZrC where at 1200°C it is not any longer limited to the carbide but extends markedly into the Fe3Al matrix. [Copyright &y& Elsevier]

Abstract: Fe-based alloys have been extensively evaluated and considered as outstanding metallic interconnect materials for fuel cell. High-energy micro-arc alloying technique has been determined to be a feasible method of producing a consistent and dense FeAl intermetallic coating on 316 stainless steel substrate. The coating had an average thickness of about 50μm and grain size was significantly refined. When exposed at 800°C, 900°C and 1000°C in air after 100h, FeAl coating on 316 SS substrate exhibited better high temperature oxidation resistance than electrode materials due to the conversion of non-protective Fe-rich scale into protective Al-rich one. FeAl intermetallic coating deposited by HEMAA will be available as interconnects for SOFC at very low costs. [Copyright &y& Elsevier]

Abstract: The biocompatibility and microstructural variation of Fe–Al–Mn (FAM)-based alloys have been investigated clearly. The ((Fe,Mn)3AlC x ) carbide (κ′-carbide) and Fe0.6Mn5.4C2 carbide (κ-carbide) as well as Cr7C3 (Cr-carbide) were formed on FAM alloy, following phase transformation by heat treatment and surface functionalization. These carbides have important role in forming nanostructure and oxidation layer. Moreover, it was found that the albumin adsorbed onto the surface increased with increasing nano-metal carbides. Therefore, heat treatment and surface functionalization such as electro-discharging and anodization not only generates a nanostructural precipitates, but also converts the alloy surface into a nanostructured oxide surface, then increasing the alloy biocompatibility. [ABSTRACT FROM AUTHOR]

Abstract: The influence of annealing atmosphere, temperature and time on the surface oxidation and vacancy condensation behavior of {111}-oriented single crystals of B2-type FeAl was investigated. AFM observation showed that as-annealed surfaces under a high vacuum were rugged and covered with a thin oxide film. The results obtained by TEM indicated that the thin oxide film was {001}-oriented κ-Al2O3 epitaxially grown on the {111}-oriented FeAl surface. AES measurements showed that the thickness of the oxide film was almost twice as thick as that of the passive Al2O3 film formed on the FeAl surface in an ambient atmosphere. It was found that the growth of surface mesopores is attributable to both the condensation of supersaturated vacancies in FeAl substrate and the Kirkendall effect by the surface oxidation during the vacuum annealing. [Copyright &y& Elsevier]

Abstract: A new methodology for the synthesis of pillared clays with Al–Fe and Al–Fe–Ce was developed, in which the clay is added directly to the pillaring solution, and microwaves or ultrasound are used in the synthesis of the pillaring solution as well as in the intercalation process. That methodology allows the volumes of water and the processing time to decrease significantly compared to the conventional method of synthesis of pillared clays. The analysis of XRD, XRF and adsorption–desorption isotherms show that the synthesized solids present more intense and homogeneous signals of pillaring and better texture properties than the clay pillared using the conventional method of synthesis. The XPS analysis shows that the Fe and Ce species are located preferably in the inner parts of the pillared clays. The catalytic activity of the pillared clays was evaluated in the phenol oxidation reaction in a diluted aqueous medium where the synthesized materials showed catalytic properties comparable to those of the materials synthesized through the conventional method reported in the literature. [Copyright &y& Elsevier]

Porous FeAl alloy was prepared by Fe and Al elemental reaction synthesis. The cyclic oxidation evolutions of porous Fe–40 at.%Al alloy at the elevated temperatures of 600 and 800 °C in air were studied and compared to porous materials of Ti, Ni, and 316L stainless steel. It has been shown that the oxidation of porous Fe–40 at.%Al alloy fitted a power law and no spallation was found after cyclic oxidation for 202 h in air. The porous FeAl alloy exhibits much better oxidation resistance than other porous materials, such as Ti, Ni, and 316L stainless steel, indicating that the porous Fe–40 at.%Al alloy has the highest structural stability at the elevated temperature in the oxidation atmosphere. Thus, the porous FeAl alloy can be used as filtering materials at elevated temperature in the oxidation atmosphere. [ABSTRACT FROM AUTHOR]

The state of surface adsorption sites in the IK-42-1 oxide catalyst for ammonia oxidation depending on catalyst preparation conditions (the nature of raw materials and the temperature of calcination) was studied in this work with the use of the diffuse reflectance IR spectroscopy of the adsorbed NO probe molecule. Hematite, which was prepared by a sulfate or chloride technology, was used as the starting raw material; Al2O3 binding agents were prepared by the reprecipitation or hydration of thermally activated gibbsite; and acetic or nitric acid was used as an electrolyte. The samples were calcined at 900–1000°C. It was found that mono- and dinitrosyl complexes with reduced coordinatively unsaturated Fe2+ cations and nitrite-nitrate complexes were formed upon the adsorption of NO on the catalyst surface (regardless of the catalyst preparation conditions). The samples differed in the amount and degree of coordinative unsaturation of adsorption sites depending on the preparation conditions. It was concluded that the most coordinatively unsaturated Fe2+ adsorption sites observed were formed on the surface of a solid solution of iron cations in aluminum oxide, which was formed in the course of catalyst preparation. It was found that an increase in the catalyst calcination temperature resulted in a decrease in the number of coordinatively unsaturated adsorption sites, which correlated with the observed decrease in the yield of NO. This correlation had the shape of a saturation curve, which can reflect the occurrence of a reaction in the diffusion mode at high degrees of conversion for the majority of catalysts. [ABSTRACT FROM AUTHOR]

Abstract: The present paper focuses on the investigation of the relationship between microstructure of Fe3Al prepared by hot isostatic pressing (HIP) and kinetics of alumina layer formation during oxidation at 900°C, 1000°C and 1100°C. As prepared HIPed Fe3Al sample reveals lamellar microstructure with inhomogeneous Al distribution which originates from the preliminary mechanical activation of Fe–Al mixture. At 900°C, Fe3Al oxidation is characterized by selective growth of very rough alumina layer containing only transient aluminium oxides. In addition to these transient oxides, α-Al2O3 stable phase is formed at 1000°C. At the highest temperature (1100°C), continuous and relatively smooth alumina layer mainly contains fine crystallites of α-Al2O3. The initial lamellar structure and phase inhomogeneity in as-HIPed Fe3Al samples are supposed to be the main factors that determine observed peculiarities after Fe3Al oxidation at 900°C and 1000°C. [Copyright &y& Elsevier]

Abstract: The paper presents the results of oxidation tests of Fe3Al-based alloys containing additions of Cr, Zr, B, and C, with and without an aluminide coating. The coating was formed by a pack cementation process in which the surface of material got enriched in aluminum. The Al-rich layer was intended to enhance the tendency of Al2O3 formation. The slow-growing Al2O3 scale provides the best corrosion protection for structural materials at high temperatures. The cyclic oxidation tests were performed in laboratory air at 1373K. The structure and composition of oxide scales as well as their adherence were evaluated and compared for the materials with and without aluminide coatings. Surface enrichment in aluminum and effect minor addition of Zr on oxidation behavior was discussed. [Copyright &y& Elsevier]

For many years Fe[sub 3]Al based alloys have been of interest because of their excellent oxidation and sulphidation resistance. However, there are still some obstacles to industrial application of these materials, including the poor hot workability of Fe[sub 3]Al based alloys. Four types ofhot working (hotrolling, hotforging, hotpressing, and hotpressing plus hot forging) for the processing of Fe[sub 3]Al ingots have been studied in the present work, and the results indicate that a combination of hot pressing and hot forging might be an optimal method for breakdown of the Fe[sub 3]Al ingot. [ABSTRACT FROM AUTHOR]

FeAl coatings were deposited on various steel substrates in a cathodic arc deposition system using FeAl alloy cathodes containing 40 and 45 at.% Al. The effects of total gas pressure (argon) and bias voltage on the morphology of the coatings were studied. Coatings were porous at low bias voltages and the porosity decreased with an increase of bias voltage. The thickness of the coatings was varied from 2 to 18 μm by varying the total charge Q (also called bias Ah) on the substrate during the deposition. The average hardness and elastic modulus of 10 μm thick coatings were measured to be 250 HV and 230 GPa, respectively. Isothermal oxidation behavior of FeAl coated on 304SS and 440C steel were studied in the temperature range of 800–1000 °C. The application of FeAl coating (10 μm) on 440C steel reduced the mass gain due to oxidation by four times at 800 °C. FeAl coated 304SS showed a much lower oxidation rate than uncoated 304SS in the temperature range of 800–1000 °C. Both the coating and the oxide scale exhibited a higher resistance to spallation than uncoated steel coupons throughout the oxidation period of 600 h. We show that the excellent high temperature resistance of cathodic arc deposited FeAl coatings can be used to protect conventional steels. [Copyright &y& Elsevier]

Iron-aluminide has the potential to be used as a superior high temperature oxidation and sulfidation resistant coating on less corrosion resistant materials. A process for producing a dense, hard, iron-aluminide coating on a mild steel substrate has been successfully developed using pulsed laser assisted powder deposition (LAPD). The clad deposition rate, measured by clad height, increased with an increase in duty cycle of the laser, either through an increase in pulse duration or frequency, an increase in powder feed rate and decrease in substrate velocity. A simple analysis using concepts of an effective interaction time, energy and powder deposition density, all of which were determined by laser duty cycle, powder feed rate and substrate velocity, was developed. Taken together these three parameters allow a determination of the processing conditions that will give rise to a high quality Fe&z.sbnd;Al clad on mild steel with a specified height. [Copyright &y& Elsevier]

The oxidation kinetics of two ODS Fe-Cr-Al alloys, PM 2000 and MA 956, were studied in oxygen and in air under isothermal conditions from 1000 to 1300°C. They both form an α-alumina scale and have good oxidation resistance, without any mass loss. Although the aluminum content in these alloys is higher than the minimum Al content necessary to ensure the growth of a continuous alumina scale, an aluminum depletion occurred in the substrate. This depletion allows the determination of aluminum diffusion coefficients in the ODS alloy. This method is very original and interesting as no Al-stable isotope is available. Moreover, the evolution of the aluminum concentration in the substrate allows one to determine the lifetime of these alloys: indeed, when the aluminum content decreases and becomes lower than a critical value, alumina can no longer form, and less-stable oxides grow very rapidly compared to alumina. [ABSTRACT FROM AUTHOR]

A sheet Fe–40at.%Al alloy with 200μm thickness was oxidized isothermally in air at temperatures between 1073 and 1473 K for up to 608.4 ks. The oxidation behavior was classified into three temperature ranges. At temperatures below 1223 K a mixture of α- and θ-Al2O3 grew fast, followed by slow oxidation with the formation of only α-Al2O3. The initial rapid oxidation is due to the formation of θ-Al2O3. Between 1273 and 1323 K the oxidation obeyed a parabolic rate law over the whole oxidation time with the formation of α-Al2O3 scale, except for the very initial stage of oxidation up to 3.6 ks. At temperatures above 1423 K the parabolic rate constants tended to decrease with oxidation time, while the oxide grain size of the columnar structure increased by 3–4 times. The change in the parabolic rate constants with time at 1473 K was reasonably well explained using the oxygen inward diffusion model along the grain boundary with a hypothetical width of 2 nm. The Fe–40Al showed the lowest oxidation rate and the activation energies for a parabolic Al2O3 growth are 422 kJ/mol above 1273 K and 241 kJ/mol below 1223 K. Oxide scale exfoliation was not observed for the Fe–40Al oxidized isothermally in air at the experimental temperatures here. [Copyright &y& Elsevier]

Effect of temperature on the oxidation behaviour of Fe3Al–Fe3AlC0.69 and FeAl–Fe3AlC0.69 alloys were studied. Physical metallurgy of these alloys with change in temperature was discussed along with the inversion of oxidation based on the Fe–Al–C phase diagram. Two kinds of inversion in oxidation were observed; in Fe3Al–Fe3AlC0.69 alloys inversion was attributed to the reduction in Fe3AlC phase, whereas in FeAl–Fe3AlC0.69 alloys it was due to the preferential oxidation of Al from the FeAl phase. A schematic model was drawn to explain these inversions of oxidation behaviour. [Copyright &y& Elsevier]

Oxidation of a Fe-7.4 at.% Al alloy at 1173 K in oxygen at 1 atm pressure resulted in the formation of a rust-colored film, shown by Auger spectroscopy to be a duplex layer consisting of an outer Fe-rich oxide over an Al-rich oxide. Mössbauer spectroscopy revealed that the outer layer was hematite containing ∼10 at.% Al and that the inner alumina layer contained some Fe. [ABSTRACT FROM AUTHOR]