Browsing by Author "Nigel, Simms"

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    Impacts of temperature and surface finish upon steam oxidation of austenitic steel TP347HFG
    (Elsevier, 2017-11-22) Bouvet, Justin; Sumner, Joy; Nigel, Simms
    The effects of the steam oxidation process on an austenitic steel (TP347HFG) exposed under isothermal conditions between 600 and 800 °C for up to 2500 h have been investigated. Samples with both as-received and ground surfaces have been exposed and the impact of surface finish on the oxidation process analysed using scanning electron microscopy with energy dispersive X-ray analysis. Exfoliated oxide flakes have also been examined to characterise their microstructures on fractured sections as well as external and spalled surfaces. Microscopic analyses demonstrated that ground surfaces possess better steam oxidation resistance than as-received surfaces due to their ability to form a more protective chromium-rich layer. The formation of regions of thicker multi-layered oxides was noted on both types of surface finish, covering large areas on as-received surfaces and only nodules on ground surfaces (spreading with increasing exposure temperature and time).
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    The role of superalloy precipitates on the early stages of oxidation and type II hot corrosion
    (2017-10-07) Potter, Andrew; Sumner, Joy; Nigel, Simms
    To meet materials challenges encountered in gas turbines, superalloys have been developed for high temperature, strength, oxidation and corrosion resistance. One strengthening method is using refractory metal additions to form carbide precipitates. However, such precipitates may be detrimental to the alloy’s environmental resistance. This paper reports how refractory metal carbide precipitates affect the early stages of oxidation and hot corrosion of two alloys: Rene 80 (nickel-based) and MarM 509 (cobalt-based). Samples were exposed at 700 °C in either dry synthetic air or 90 ppm SOx, 10·5% CO2, 8·5% O2, 5% H2O (balance N2) with a 80/20 (Na/K)2SO4 deposit (1·5 μg/cm2/hour flux). The oxidation morphology and corrosion products were investigated by scanning electron microscope and energy dispersive X-ray analysis, to show that refractory metal carbide precipitates close to the metal surfaces disrupt protective oxide scale formation, thus providing inward transport routes for corrosive species.