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RESEARCH PRODUCT

High temperature alloy chloridation at 850°C. Part I: Comparison of Ni-based and Fe-based alloy behaviour

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Eight alloys were tested under Ar/Cl 2 atmosphere at 850 °C for 15 min and 1 h. Their gross and net weights were evaluated together with the base metal consumption. Macroscopic and microscopic micrographs, associated with chemical analyses and X-ray diffraction gave the composition and microstructure of the corrosion products. Huge differences were observed if one compared the nickel based alloy behaviour to that of the iron based alloy. Molybdenum and tungsten could also play a role, but it was not clearly defined until now. A tentative evaluation of the best candidates will be given, according the experimental conditions of this work and the chosen criteria. A corrosion index was established after each observation and helped to classify the different material behaviour under chloridation. The Ni-based alloys possessed the best chloridation behaviour in the present conditions, followed by the Ni-based alloys containing more Cr and finally by the Fe-based materials. The chloridation behaviours were discussed according to the volatility of the chlorides species formed on the different alloys.