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What If the Protection against Oxidation of chromia-forming alloys Was Not Always Due to the chromia Layer?

American Journal of Analytical Chemistry 2024年第9期15卷 286-302页

作者： Boris Contri Stéphane Valette Marina Soustre Pierre Lefort IRCER European Ceramics Centre UMR CNRS 7315 University of Limoges 12 rue Atlantis Limoges Cedex France

chromia-forming alloys have good resistance to oxidizing agents such as O2, CO2, … It is accepted that the protection of these alloys is always due to the chromia layer formed at the surface of the alloys, which acts as a barrier between the oxidizing gases and the alloy substrates, forming a diffusion zone that limits the overall reaction rate and leads to parabolic kinetics. But this was not verified in the study devoted to Inconel®625 the oxidation in CO2 that was followed by TGA, with characterizations by XRD, EDS and FIB microscopy. Contrary to what was expected and accepted in similar studies on other chromia-forming alloys, it was shown that the diffusion step that governs the overall reaction rate is not located inside the chromia layer but inside the alloy, precisely inside a zone just beneath the interface alloy/chromia, this zone being depleted in chromium. The chromia layer, therefore, plays no kinetic role and does not directly protect the underlying alloy. This result was demonstrated using a simple test that consisted in removing the chromia layer from the surface of samples partially oxidized and then to continue the thermal treatment: insofar as the kinetics continued without any change in rate, this proved that this surface layer of oxide did not protect the substrate. Based on previous work on many chromia-forming alloys, the possibility of a similar reaction mechanism is discussed. If the chromia layer is not the source of protection for a number of chromia-forming alloys, as is suspected, this might have major consequences in terms of industrial applications.

关键词： chromia-forming alloys chromia Layer Oxidation Protection Inconel®625 Kinetics

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CO_(2) High Temperature Corrosion and Its Prevention of chromia forming Fe-base alloys

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表面技术 2021年第4期50卷 260-266页

作者：张建强 School of Materials Science&Engineering University of New South WalesSydney NSW2052Australia

High temperature corrosion of chromia forming Fe-base alloys by CO_(2) produces not only oxidation but also *** corrosion kinetics in CO_(2)-rich gas is found to be increased compared with that in air or *** a result,higher alloy chromium levels are required to achieve protective chromia formation in CO_(2).Corrosion reaction mechanisms in CO_(2) are examined and the internal carburisation of alloys in low carbon activity CO_(2) gases are analysed based on the variation of pO_(2) at the interface of oxide and *** penetration through chromia oxide scale has been revealed by atom probe *** strategies to resist CO_(2) corrosion are reviewed by alloying of Si and/or Mn,forming additional diffusion barrier layers,and by adding sulphur to modify oxide grain boundaries to reduce carbon diffusion along the grain boundaries.

关键词： high temperature corrosion CO_(2) chromia-forming alloys carburisation alloying

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