Evaluation of Sulfidation Resistance of Atomized Fe40Al Based Intermetallics
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Evaluation of Sulfidation Resistance of Atomized Fe40Al Based Intermetallics M. A. Espinosa-Medina1,*, G. Carbajal de la Torre1, A. Martínez-Villafañe2, J.G. GonzálezRodríguez3. 1
Facultad de Ingeniería Mecánica, UMSNH, C.P. 58000, Morelia, Mich., México. 2 CIMAV, Complejo Industrial Chihuahua, Chihuahua. México. 3 UAEM-CIICAP, Av. Universidad 1001, Col. Chamilpa, Cuernavaca, Morelos, México. * Email: [email protected] ABSTRACT The isothermal oxidation-sulfidation of Fe-40Al based intermetallics alloys in N2/SO2 gas mixture at 625, 700 and 775°C were evaluated. Fe40Al, Fe40Al+0.1B, Fe40Al+0.1B+10Al2O3 alloys were produced by atomization and deposition. Isothermal gas exposition was reached during 48 hours. FeAl based alloys showed good sulfidation resistance, presenting both small weight gain and weight change fluctuations. At 625°C, the Fe40Al+0.1B alloy had the biggest weight gain; on the other hand the Fe40Al alloy exhibited the biggest sulfidation resistance. At 700 and 775°C, the Fe40Al+0.1B alloy presented the smallest weight gain, however Fe40Al alloy presented higher weight gain, that is to say, the smallest sulfidation resistance at those temperatures. The variation in the weight gain curves were discussed in terms of formation and detachment of sulfides, and by local attack on the alloy surface as the temperature increasing. The results are supplemented with characterization by SEM and analysis of X-rays dispersion. Keywords: Alloy, Oxidation, Thermogravimetric analysis (TGA), Corrosion, Scanning electron microscopy (SEM) INTRODUCTION In several high-temperature corrosion processes, the degradation of materials by sulfidation continues being a serious problem, due degradation mode cannot be substantially inhibited even using high performance super alloys as: high-chromium steels. Consequently, a need for improvement the sulfidation resistance is important. The sulfidation/oxidation process in gases at high temperatures can be call just as a process of oxidation [1]. There are several conditions in the industry where structural materials are exposed to sulfur containing atmospheres at high temperature [2]. It is well known that under theose conditions, the corrosion of the common metals (Fe, Ni, Co) and the oxidation resistant alloys is much more severe than in pure oxidizing environments. The scale kind formation improves high or low oxidation resistance; in the iron aluminides exposed to sulfur content gases at high temperatures depends on the nature of sulfur compounds and its partial pressures of compounds. However, in the aluminides, Al2O3 can even be formed at very low oxygen pressures with a significant activity of sulfur contents [3]. In vapor of both pure sulfur and H2S/H2 mixtures, the alumina is not formed. Nevertheless, the binary alloys of iron-aluminum with higher contents than 18 at.% of Al continue having good resistance up to the 750°C [4-6]. At 750° and 900°C in sulfur vapor at 10-3 Pa pressures, the alloy Fe3Al with 28at.%Al forms an external Al2S3 film, but a sulfur pressure superior
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