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Poster De Conférence Année : 2009

Metallography study of the surface states of alloys heated at very high temperatures in oxidizing conditions

Patrice Berthod
Johann Ravaux

Résumé

In service, the refractory alloys used in the hottest parts of industrial machines may accidentally encounter extremely high temperatures, which even can reach their solidus temperature. If these very high temperatures are only several tens Celsius degrees bellow the alloy solidus temperature several hours can be enough to significantly modify the microstructure of the alloy as well as its chemical composition in sub-surface, and then the resistance of the alloy against hot oxidation. If this temperature is slightly higher than the fusion start temperature of the alloy, this one can be partially molten and some liquid zones can be more or less exposed to oxidation, in some cases separated from the oxidizing gases by a thin layer of alloy or directly exposed to these gases. Such conditions may lead to fast catastrophic oxidation inward the bulk. The purpose of this work is to specify the surface state of several alloys in order to assess their remaining potential of resistance against hot oxidation. The three Ni alloys and the two Co-based superalloys correctly resisted to oxidation at these four very high temperatures, even if they are partially molten. This can be attributed first to the initial high Cr content in all the alloys (28 to 30wt.%) and also, in the case of 1328°C for which all alloys were partially molten, to the single-phase zone formed by oxidation at heating which prevents thereafter any contact between the oxidizing gases and these molten areas, and then possible catastrophic oxidation. The minimal chromium contents on extreme surface let think that the resistance of the alloys against hot oxidation may go on several supplementary hours.

Domaines

Chimie
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Dates et versions

hal-03792432 , version 1 (30-09-2022)

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  • HAL Id : hal-03792432 , version 1

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Patrice Berthod, Johann Ravaux. Metallography study of the surface states of alloys heated at very high temperatures in oxidizing conditions. Eurocorr 2009, Sep 2009, Nice, France. ⟨hal-03792432⟩
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