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Poster De Conférence Année : 2008

Correlation between the external oxide scale adherence and the bulk's thermal expansion behaviour for several carbidesstrengthened refractory alloys

Patrice Berthod

Résumé

During thermal cycles at high temperature the alloys are currently affected by a partial or total loss of the oxide scale formed before on their external surface. This loss of the protective oxide layer, which accelerates the degradation of most alloys during their use in practical conditions, is logically attributed to the thermal contraction during cooling. The thermal expansion or contraction phenomenon can depend on the microstructure of the alloy, notably on the nature of its matrix and on its carbide volume fraction. The aim of the present study is to characterize the progress of the spallation during cooling by exploiting the cooling parts of thermogravimetry curves, in the case of cast alloys belonging to different families (chromium­rich Co­based, Ni­based and Fe­based alloys, with or without interdendritic carbides) and to try to correlate this with their thermal expansion behaviours. Despite their low efficiency because of variation of the apparent weight of the oxidized samples due to decreasing temperature, the last part of the thermogravimetry measurements can be of great interest for specifying, not really the mass of lost oxide during cooling, but temperatures at which these losses occurred. For example this allows knowing if the loss of external oxide which can be observed on sample at room temperature acted abruptly at a given temperature or on the contrary was diluted along a temperature range which can be also determined. Here this allowed, for example, seeing that the external oxide covering nickel or cobalt alloys was lost after less cooling than for iron alloys which exhibit lower coefficients of thermal expansion, i.e. less far from the oxides ones.
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hal-03876364 , version 1 (28-11-2022)

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Patrice Berthod. Correlation between the external oxide scale adherence and the bulk's thermal expansion behaviour for several carbidesstrengthened refractory alloys. Eurocorr 2008, Sep 2008, Edinburgh, United Kingdom. . ⟨hal-03876364⟩
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