Dorota Pasek

This work presents a study of oxide-scale development on a B2 FeAl-based alloy (Fe40Al5Cr0.2TiB) during long-term isothermal oxidation at 700 °C in air, with particular emphasis on the effect of plastic processing. Oxidation tests were conducted for 300, 1000, and 2000 h. Surface morphology and chemical composition were examined using SEM/EDS, phase composition was identified by XRD, and local oxide thickness was measured by TEM. Surface topography was quantified by optical profilometry using Ra and Rz parameters. In both material states (as-cast and plastically processed), the alloy formed a continuous α-Al₂O₃-based scale. Plastic processing significantly affected oxidation kinetics, resulting in higher mass gain compared to the as-cast condition. Despite differences in mass gain, the average oxide-scale thickness after 2000 h remained in the submicrometric range (~340 nm) for both states. Surface topography analysis revealed differences in roughness and morphology associated with the material condition. The results demonstrate that plastic processing influences oxidation behavior primarily through microstructural modification, while the protective character of the alumina scale remains preserved. These findings provide data relevant to FeAl-based materials considered for high-temperature energy applications.

The present study investigates the morphology, chemical composition, and phase constitution of oxide scales formed on the Fe40Al5Cr0.2TiB intermetallic alloy after long-term oxidation at 700 °C for 2000 h in air and water vapor environments. The results demonstrate the formation of an extremely thin oxide scale (≈300 nm), composed predominantly of α-Al₂O₃, which provides effective protection against further oxidation. The oxide layer exhibits locally heterogeneous morphology, including whisker-like structures and fine crystallites. Due to the very limited thickness of the oxide scale, significant challenges arise in the interpretation of microanalytical data. It is shown that the accelerating voltage strongly influences the effective information depth in SEM-EDS analysis, leading to a substantial contribution from the substrate even at low voltages. Monte Carlo simulations were used to support the interpretation of electron–matter interactions and to explain the observed discrepancies in chemical analysis. The study demonstrates that reliable characterization of ultrathin oxide scales requires careful optimization of SEM parameters and the combined use of complementary techniques, including EDS/WDS, XRD, and EBSD. The findings highlight the importance of methodological considerations in the analysis of thin oxide layers and provide guidance for the correct interpretation of experimental data in similar systems.

This paper presents the results of corrosion resistance tests of materials (Fe40Al5Cr0.2ZrB alloy and X18CrN28 steel) in a 5% NaCl solution at room temperature using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization, complemented by confocal/AFM topography and SEM/EDS analysis. Confocal/AFM mapping showed pronounced roughening and localized features on Fe40Al5Cr0.2ZrB alloy (e.g., S_a rising locally to ~1.63 μm), consistent with heterogeneous chloride-induced attack, whereas X18CrN28 steel exhibited only minor roughness changes (S_a ~ 13–19 nm). SEM/EDS of Fe40Al5Cr0.2ZrB alloy revealed mixed oxides with detectable chlorine at corroded sites, while the steel retained a thin, Cr-rich passive layer with negligible Cl signal. Overall, X18CrN28 steel demonstrates significantly higher resistance to localized corrosion in neutral chloride media than Fe40Al5Cr0.2ZrB alloy, aligning electrochemical metrics with surface and chemical analyses.

The surface of the Fe40Al5Cr0.2TiB alloy, after oxidation in steam at 700 °C, showed a varied morphology dependent on oxidation time. Initially, a fine, acicular oxide layer formed, which over time transformed into a more compact, lumpy structure corresponding to the α-Al₂O₃ phase. EDS analysis confirmed the dominance of aluminum and oxygen in the oxidation products, and XRD studies revealed the presence of the α-alumina phase. Optical profilometry revealed a significant increase in roughness parameters (R_a and R_z) after long-term exposure (2000 h), which correlates with the thickening and sinterization of the oxide layer. The obtained results indicate that in a water vapor environment, a stable α-Al₂O₃ phase can already be formed at a temperature of 700 °C, and its development leads to increased roughness.

The paper presents the results of oxidation tests on the alloy based on the intermetallic phase, Fe40Al5Cr0.2TiB, in the air at 700–1000 °C temperature. The kinetics of corrosion processes were determined, the surface condition after oxidation was assessed, and the type and morphology of the oxides formed were determined. In addition, the paper presents the possibility of applying the technology of surfacing Fe40Al5Cr0.2TiB alloy on the surface of steel grade S235JR as a protective coating that is resistant to high temperatures. The process was carried out using the TIG method by direct current (DC). After the surfacing, the structure of the surfacing weld made of the tested material on the base of structural steel grade S235JR was determined. It was found that a protective Al2O3 oxide layer is formed on the surface of the oxidized alloy based on the intermetallic phase from the FeAl system, and the oxidation kinetics have a parabolic course. Moreover, it was found that the morphology of the oxides formed on the surface varies depending on the oxidation temperature, which clearly indicates a different mechanism of oxide layer formation. The formation of a stable α-Al2O3 oxide variety on the surface of the Fe40Al5Cr0.2TiB alloy protects the material from further corrosion, which favors the application of this alloy on structures and fittings operating at elevated temperatures. The aim of the research was to use the Fe40Al5Cr0.2TiB alloy with very good oxidation resistance as a layer overlay on ordinary quality S235JR steel. In this way, conditions were created that fundamentally changed the surface condition (structure and physicochemical properties) of the system: steel as a substrate—intermetallic phase Fe40Al5Cr0.2TiB as a surfacing layer, in order to increase resistance to high-temperature corrosion and erosion (in the environment of gases and solid impurities in gases) often occurring in corrosive environments, especially in the power industry (boilers, pipes, installation elbows) and the chemical industry (fittings). At the same time, the surfacing method used is one of the cheapest methods of changing the surface properties of the material and regenerating or repairing the native material with a material with better properties, especially for applications in high-temperature corrosion conditions.

This article shows the results of research conducted on the corrosion resistance of the FeAl (Fe40Al5Cr0.2TiB) alloy in two variants: the alloy after casting and after homogenization annealing (1000 °C, 93 h). Analysis of the microstructure of these alloys was conducted on the light microscope, and the phase composition was determined by X-ray diffraction. Resistance to electrochemical corrosion was tested in a 5% NaCl solution using the potentiodynamic polarization technique and electrochemical impedance spectroscopy. The surface of alloys after corrosion tests was examined by scanning electron microscopy. Chemical composition tests were conducted using an energy-dispersive X-ray spectrometer. The structure analysis was made with an electron backscatter diffraction detector. Based on the studies, it was found that the corrosion resistance of the FeAl alloy after homogenization annealing was higher than that of the FeAl alloy after casting. This alloy showed a more non-homogeneous and coarse-grained microstructure compared to the alloy after homogenization annealing. The investigation of the surface condition of FeAl alloys after corrosion tests showed the presence of pits, particularly in the case of the alloy after casting.

The paper presents the results of tests on the corrosion resistance of Fe40Al5Cr0.2TiB alloy after casting, plastic working using extrusion and rolling methods. Examination of the microstructure of the Fe40Al5Cr0.2TiB alloy after casting and after plastic working was performed on an Olympus GX51 light microscope. The stereological relationships of the alloy microstructure in the state after crystallization and after plastic working were determined. The quantitative analysis of the structure was conducted after testing with the EBSD INCA HKL detector and the Nordlys II analysis system (Channel 5), which was equipped with the Hitachi S-3400N microscope. Structure tests and corrosion tests were performed on tests cut perpendicular to the ingot axis, extrusion direction, and rolling direction. As a result of the tests, it was found that the crystallized alloy has better corrosion resistance than plastically processed material. Plastic working increases the intensity of the electrochemical corrosion of the examined alloy. It was found that as-cast alloy is the most resistant to corrosion in a 5% NaCl compared with the alloys after hot extrusion and after hot rolling. The parameters in this study show the smallest value of the corrosion current density and corrosion rate as well as the more positive value of corrosion potential.