Browsing by Author "Schlereth, Clara"

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    Influence of surface treatment on metal dusting resistance of welds
    (Weinheim [u.a.] : Wiley-VCH, 2023-09-21) Schlereth, Clara; White, Emma M.H.; Lepple, Maren; Nowak, Benedikt; Hattendorf, Heike; Galetz, Mathias C.
    Welds of the commercial Ni‐based alloys 602 CA, 699 XA, 601 and 690 were exposed under harsh metal dusting conditions. The pit formation was compared for as‐welded, brushed, ground, glass bead blasted, steel shot peened and dry cathodic pickled surfaces. Surface treatments were applied by industrial partners. When (stainless) steels were involved in the surface treatment, Fe contaminations acted as catalyst sites for pit initiation. A fast metal dusting attack was also observed on dry cathodic pickled samples. A beneficial effect was attributed to deformation of the sub‐surface zone, as it provides diffusion paths for oxide formers (by grinding and glass bead blasting). In the same region, formation of α‐Cr (BCC) precipitates was observed. The best performance was found for samples where the weld bead was fully flattened by grinding to P40 grit. In addition, it was demonstrated that on‐site slurry aluminization further enhances the resistance against metal dusting attack.
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    Oxide scale microstructure and failure mechanism of alloy 601 under varying metal dusting conditions
    (Dordrecht [u.a.] : Springer Science + Business Media B.V, 2024-01-08) Schlereth, Clara; Weiser, Martin; White, Emma M. H.; Felfer, Peter; Galetz, Mathias C.
    Chemical plants which process highly carbonaceous gases at elevated temperatures are prone to catastrophic corrosion by metal dusting. Typically, commercial alloys with high amounts of protective oxide scale formers (Cr, Al, and Si) are used in these environments. However, scale failure is still frequently observed after an incubation time initiating pits. In this study, the microstructure and subsequent metal dusting-induced failure of the oxide scale on the commercial Ni-based alloy 601 was analyzed. Samples were exposed in different aggressive metal dusting gases and characterized using metallographic cross-sections, electron beam microanalysis (EPMA), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and transmission electron microscopy (TEM). A thin and protective chromia scale formed in some regions with a continuous silica layer below. Across most of the alloy 601 surfaces, internal oxidation of Al could be linked to metallic particles in the outer scale. Additionally, MnCr2O4 was observed in the outer scale. Together with pores in the chromia, the spinel and metallic particles in the outer scale combined to provide pathways for carbon ingress. After exposure in a gas with a higher driving force for carbon deposition, a higher amount of carbon was incorporated in the growing oxide scale, resulting in earlier scale failure and metal dusting pit initiation.