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    Effect of the incorporating of refractory NbC precipitates in intermetallic iron-aluminide coatings on corrosion and high-temperature oxidation behavior
    (Elsevier Science Sa, 2024) Gunen, Ali; Altinay, Yasemin; Sabun, Sahin; Alkan, Sabri
    This study aims to investigate the effects of growing niobium carbide (NbC) particles into intermetallic iron-aluminide (FeAl) coatings on ductile cast iron (SGI) by thermo-reactive diffusion technique (TRD). The study compares the corrosion and oxidation behavior of the FeAl-NbC coatings with SGI, FeAl, and NbC coatings. Corrosion tests were conducted through polarization tests in a 3.5 wt% NaCl solution, while oxidation tests were performed at 900 degrees C for 4, 16, and 64 h. Before and after corrosion and oxidation tests, the coatings were examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The findings show that FeAl coatings with NbC particles had lower graphite nodules, porosity, and surface roughness values compared to FeAl coatings. FeAl-NbC composite coatings provided better corrosion and oxidation resistance compared to untreated SGI, FeAl, and NbC coatings. The results of the comparative analysis of FeAl-NbC, FeAl, NbC, and untreated SGI specimens indicate that corrosion resistance in a 3.5 wt% NaCl solution and oxidation resistance at 900 degrees C followed the order FeAl-NbC > FeAl > NbC > SGI.
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    Microstructural characterization and high-temperature wear behavior of refractory niobium-carbide growth in intermetallic iron-aluminide coatings
    (Pergamon-Elsevier Science Ltd, 2024) Gunen, Ali; Altinay, Yasemin; Sabun, Sahin
    Iron-aluminide (Fe-Al) intermetallics are characterized by their high-temperature oxidation resistance. However, their use in tribo-corrosive environments is limited due to their low hardness and brittle nature. To overcome this weakness, the feasibility of forming composite coatings (NbC-FeAl) by intercalation of refractory NbC particles into Fe-Al coatings by thermo-reactive diffusion technique and its effect on high-temperature wear behavior was investigated in this study. The coatings obtained underwent comprehensive characterization using scanning electron microscopy, X-ray diffraction, microhardness measurements, and ball-on-disc wear tests, providing valuable insights into their properties. The characterization studies showed that increasing the growth of NbC in the intermetallic iron-aluminide content resulted in a slight increase in the hardness and a decrease in the thickness of the iron-aluminide layer. Moreover, the formation of NbC in Fe-Al coatings increased the dislocation densities of the coatings, resulting in an improvement of wear resistance 2.7 times at room temperature and up to 3.5 times at 500 degrees C. While different wear mechanisms occurred in coated samples at room temperature, the dominant wear mechanism at 500 degrees C evolved into an oxidatively supported adhesive wear mechanism. This study showed that Fe-Al coatings exhibited better wear response at both room and elevated temperatures when reinforced with NbC.