Deposition of Manganese and Cobalt on Ferritic–Martensitic Steels via Pack Cementation Process (original) (raw)
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Development of novel diffusion coatings for 9-12 % Cr ferritic-martensitic steels
Materials and Corrosion, 2005
Eventhough 9-12% Cr steels are mechanically designed for power plant applications up to 650 C, their effective use is limited by the corrosion resistance at this temperature. Therefore, the present paper addresses the development of diffusion coatings on 9% Cr ferritic-martensitic steels. The difficulty of coating these materials with conventional diffusion processes arises from the temperature limit above which the conversion of the martensite is accelerated and the mechanical properties would be deteriorated. Aluminide coatings consisting of Fe 2 Al 5 or FeAl phases were thus developed for deposition temperatures between 650 and 715 C by the conventional pack cementation technique. As the addition of boron was expected to improve the oxidation properties of the coating, the influence of B on the aluminide coating was investigated. The precedent diffusion of Cr as an interdiffusion barrier before switching to the Al diffusion step was also investigated. As a further technique, the fluidised bed chemical vapour deposition (FBCVD) method allowed the development of Fe 2 Al 5 coatings at 550 C. Furthermore, Si or codiffusion Al-Si coatings were developed at temperatures as low as 550 C.
Coatings, 2020
A chromium diffusion coating was applied on an oxide dispersion strengthened ferritic-martensitic (ODS-FM) steel to improve oxidation resistance at high temperature. By carrying out physical vapor deposition followed by inter-diffusion heat treatment, a thin Cr-rich carbide layer was produced on the ODS-FM steel. Both the as-received and surface-modified specimens were oxidation-tested at 650 °C in air and steam environments for 500 h. The surface-modified specimens showed improved oxidation resistance in both environments. In an air environment, both conditions exhibited a thin and continuous chromia layer, but the formation of Cr2O3 and (Mn, Cr)3O4 nodules resulted in greater weight gain for the as-received specimen. In a steam environment, weight gain increased for both the as-received and surface-modified specimen. Especially, the as-received specimen showed much greater weight gain with the formation of a thick oxide layer consisted of outer Fe-rich oxide and inner (Fe, Cr, Mn)...
High Temperature Corrosion of Chromium–Manganese Steels in Sulfur Dioxide
Oxidation of Metals, 2005
This work was aimed at explaining the corrosion mechanism of commercial Cr–Mn steels at 1073, 1173 and 1273 K in the atmospheres containing oxygen and sulfur. Three steels were selected for the investigations, two single-phase austenitic steels (Cr17Mn17 and Cr13Mn19SiCa) and a two-phase austenitic-ferritic steel Cr15Mn19. On all studied steels triplex scales were formed. The inner very thin, fine-grained part of the scale contained manganese, chromium and iron sulfides and oxides, the intermediate layer was built mainly of the MnCr2O4 spinel while MnO was the predominant constituent of the outer scale layer. According to the gravimetric measurements, after an initial incubation period, the oxidation of steel follows a parabolic rate law. Thermodynamic and kinetic aspects of the formation of oxide-sulfide and oxide layers were discussed. Oxidation was accompanied by depletion of the subscale region of the metallic core in manganese, which is the austenite former. Consequently austenite transformed into ferrite.
Journal of Power Sources, 2008
In solid oxide fuel cells (SOFC) for operating temperatures of 800 • C or below, the interconnection plates can be made from stainless steel. This is a big economic advantage, but energy losses can be caused by undesirable reactions between the alloys and other SOFC components. The use of coatings on interconnect stainless steels can reduce this degradation. A MnCo 1.9 Fe 0.1 O 4 (MCF) spinel not only significantly decreases the contact resistance between a La 0.8 Sr 0.2 FeO 3 cathode and a stainless steel interconnect, but also acts as a diffusion barrier to prevent Cr outward migration through the coating. The level of improvement in electrical performance depends on the ferritic substrate composition. For Crofer22APU and F18TNb, with a Mn concentration of 0.4 and 0.12 wt%, respectively, the reduction in contact resistance is significant. In comparison, limited improvement is achieved by application of MCF on IT-11 and E-Brite containing no Mn. No influence of the minor additions of Si or Al is observed on contact resistance. The MCF protection layer bonds well to the stainless steel substrates under thermal cycling, but the thermal expansion difference is too large between the La 0.8 Sr 0.2 Co 0.75 Fe 0.25 O 3 contact layer used and Crofer22APU and IT-11.
International Journal of Hydrogen Energy, 2015
High velocity solution precursor flame spray process was used to deposit MnCo 1.9 Fe 0.1 O 4 and Mn 1.5 Co 1.5 O 4 coatings on Crofer 22 APU ferritic stainless steel samples. The solution precursors were manufactured by diluting metal nitrates into deionized water. The assprayed coatings were oxidized at 850 C for 500 h to evaluate Cr-barrier and electrical properties. The post-mortem studies were performed with various qualitative and quantitative elemental analysis methods and a four-point measurement was used for the area specific resistance studies. The as-sprayed coatings were formed of single crystallite nanoparticles (10e20 nm) and polycrystalline sub-micron particles (100e500 nm). The small particle and crystallite size showed strong sintering behavior during the oxidation cycle. Cr-migration was fully prevented thought the oxidized coatings. The surface topography and grain growth dominated the electrical properties during the test cycle.
Bulletin of Materials Science, 2017
Manganese-cobalt coatings are promising candidates for solid oxide fuel cell (SOFC) interconnection applications because of their high conductivity and good oxidation resistance. In the present study, manganese and cobalt are electrodeposited on Crofer 22 APU ferritic stainless steel. The effects of current density, pH, sodium gluconate (NaC 6 H 11 O 7) concentration, cobalt sulphate concentration (CoSO 4 •7H 2 O) and deposition duration on the microstructure and cathodic efficiency are characterized by means of scanning electron microscopy, weight gain measurements and energy-dispersive X-ray spectrometry, respectively. Results show that increases in current density and deposition duration lead to decrease in current efficiency and deposition rate. Increasing the pH to 2.5 causes an initial rise of current efficiency and deposition rate, followed by subsequent decline. In addition, the increases in sodium gluconate and cobalt sulphate concentrations in the electrolyte solution result in an increase in current efficiency and deposition rate. Moreover, the results demonstrate that the variations in the current density, pH, sodium gluconate (NaC 6 H 11 O 7) concentration, cobalt sulphate concentration (CoSO 4 •7H 2 O) and duration have a significant effect on grain size, uniformity and the adherence of the coating.
Materials and Corrosion, 2000
The corrosion behavior and the electrical resistivity of the oxide scale that forms on alternative materials for bipolar plates in molten carbonate fuel cells (MCFCs) were investigated. Commercial stainless steels (SS) containing cobalt (Haynes 556) and manganese (Nitronic 30, Nitronic 50, and Nitronic 60) were tested under cathodic MCFC conditions Additionally, 316L SS coated with cobalt by thermal spraying was studied. Oxide-scale resistivity measurements were coupled with observations of microstructural/compositional changes over time.
Materials Research-ibero-american Journal of Materials, 2004
In recent years a new group of ferritic-martensitic chromium steels for the use in fossil power stations has been developed with chromium contents between 9 and 12%. Typical representatives of these steels are P91, E911 and Nf616, which are nowadays widely used in the more advanced power plants. In the development phase the focus was on the mechanical properties of these steels but when taking them to practical operation conditions it turned out that much of the lifetime of the materials and components is determined by their oxidation properties. Oxidation resistance is first of all a function of alloy composition. For the steels of this group it is chromium, silicon, manganese and molybdenum that decide their oxidation performance and since the contents especially of the four elements can be significantly different for the different steels there can be clear differences in oxidation behaviour. One of the most important issues from this point of view is how the concentrations of these elements change in the metal subsurface zone during operation/oxidation since if their level drops below a critical level oxidation resistance of the steels will be lost. In the work to be reported the influence of alloy composition and metal subsurface zone concentration as a function of oxidation time up to 10000 h was investigated in dry air and air up to 10% water vapour at 650 °C. The investigations comprised several of the advanced commercial 9% Cr steels including P91, E911, Nf616 and six laboratory melts of Nf616 with different amounts of silicon. As the results of the investigations show humidity, which is omnipresent in combustion environments, can dramatically accelerate oxidation. Silicon as an alloying element reduces the detrimental effect of water vapour significantly while molybdenum has a negative effect. The effects of the key alloying elements in these steels was quantified for conditions with and without water vapour in the environment including the role of mechanical load and recommendations were developed on how to guarantee the optimum oxidation resistance of these steels.
CHANGES IN OXIDE CHEMISTRY DURING CONSOLIDATION OF Cr/Mn WATER ATOMIZED STEEL POWDER
Powder Metallurgy Progress, 2011
Modern water atomization methods allow industrial production of highpurity water atomized powder grades prealloyed with chromium and manganese. Surface coverage by oxide islands, formed by a variety of mixed oxides of chromium and manganese with higher thermodynamic stability, is below 10% which assumes good sinterability of such PM grades. However, there is still a risk of formation of oxides products on the powder surface during critical stages of powder consolidation, especially during the heating stage. Therefore present work is focused on the effect of alloying elements content on the possible scenarios of oxides' reduction/formation/transformation in Fe-Cr-Mn-C powder systems. Accurate analysis of specimens, sampled during different stages of the sintering process, by advanced analysis techniques (HR SEM+EDX) was combined with thermodynamic modelling of oxides' stability. Obtained results indicate that oxide transformation process is governed by thermodynamic stability of present oxide phases in the sequence
Study of parabolic rate constant for coated AISI 430 steel with Mn 3 O 4 and MnFe 2 O 4 spinels
2011
The oxidation resistance of AISI 430 ferritic stainless steels which are used as interconnects in solid oxide fuel cells (SOFCs) for the intermediate temperature operation can be improved with a protective coating layer. In this study, the pack cementation method is employed to coat AISI 430 ferritic stainless steel. Isothermal oxidation, cyclic oxidation and oxidation at different temperatures (600-900°C) are applied to evaluate the parabolic rate constant. The coated samples demonstrated lower parabolic rate constant ( kp) in each test and it indicates that the coating layer has acted as a mass barrier against the outward diffusion of cations specially chromium. XRD analysis revealed that the formation of Mn 3O4 and MnFe 2O4 spinels during oxidation caused to the improvement of the oxidation resistance.