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The resistance of eight alloys against chloridation was tested at 850 C in Ar/Cl 2 (2.5% Cl 2 ) for 15 min. Pre-oxidation treatments were performed for 1 h and 8 h at 850 C in order to produce a thin, adherent and protective oxide scale able to improve the chloridation behaviour of the tested materials. The chloridised sample morphologies were compared to the morphologies observed on the non pre-oxidised samples. The alloys containing a large amount of iron did not exhibit any chloridation resistance, even after preoxidation, and were severely damaged. The nickel based alloys gave interesting results but were also attacked by chloride, probably by the "active oxidation" mechanism. The duration of the pre-oxidation treatment plays an important role, since the 8 h pre-oxidation appears more beneficial than the 1 h pre-oxidation, to delay the chloridation, probably because of the best quality of the oxide layer grown during 8 h. For the nickel based materials, the effects of chloride appear less severe than for the iron-based alloys, but are not stopped. The "active oxidation" mechanism is proposed to be responsible for the degradation of the tested materials.

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.