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Investigation on Metal Dusting Corrosion Phenomena Over Incoloy 800

UNS N08800 alloy coupons were prepared, polished and oxidized in diluted steam at 540 ºC. Formation of carbon on the surface of the pre-oxidized samples was investigated by exposure to reducing, highly carburizing atmosphere (CO in Ar) at 20 bar and varying temperature (550- 750 ºC).

Product Number: 51317--9439-SG
ISBN: 9439 2017 CP
Author: Xiaoyang Guo
Publication Date: 2017
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Metal dusting corrosion is a catastrophic degradation phenomenon that initiates on metallic surfaces under carburizing atmospheres and proceeds by a gradual breakdown of the metallic matrix into fine particles composed of metals and/or carbon. This process was investigated under laboratory conditions over commercial Incoloy Alloy 800 coupons. Alloy samples were pre-oxidized in 10% steam in Ar at 540 ?C for 6 h followed by exposure to reducing highly carburizing atmosphere for 20 h. Several carburizing parameters were studied such as the temperature (550 650 or 750 ?C) and the pressure (1 or 20 bar). Two carburizing gas mixtures were used; a CO+Ar mixture with 10/90 (mol %) composition ratio and a CO/H2O/CO2/H2/Ar mixture with 20/10/15/25/30 (mol %) composition ratio to mimic industrially relevant synthesis gas. The resulting surfaces were examined by using scanning electron microscopy (SEM) depth profile analysis by Auger electron spectroscopy (AES) under ion-sputtering and transmission electron microscopy (TEM). As indicated by electron microscopy the alloy samples treated under CO+Ar at low temperature and low pressure (i.e. 550 ?C and 1 bar) showed a thick layer of surface carbon deposits. The amount of carbon formed on the surface decreases however with the exposure temperature and this requires further investigation in view of the infinite carbon activity and presumed kinetic control under such conditions. Existence of carbon formation could so far not be confirmed under the syngas mixture irrespective of the exposure temperature and pressure and this is in partial contrast to our previous investigations of Inconel 601. Further detailed characterization will be presented and discussed in view of these initial findings.

Key words: metal dusting corrosion, SEM, TEM, Auger depth profile analysis, Raman spectroscopy

Metal dusting corrosion is a catastrophic degradation phenomenon that initiates on metallic surfaces under carburizing atmospheres and proceeds by a gradual breakdown of the metallic matrix into fine particles composed of metals and/or carbon. This process was investigated under laboratory conditions over commercial Incoloy Alloy 800 coupons. Alloy samples were pre-oxidized in 10% steam in Ar at 540 ?C for 6 h followed by exposure to reducing highly carburizing atmosphere for 20 h. Several carburizing parameters were studied such as the temperature (550 650 or 750 ?C) and the pressure (1 or 20 bar). Two carburizing gas mixtures were used; a CO+Ar mixture with 10/90 (mol %) composition ratio and a CO/H2O/CO2/H2/Ar mixture with 20/10/15/25/30 (mol %) composition ratio to mimic industrially relevant synthesis gas. The resulting surfaces were examined by using scanning electron microscopy (SEM) depth profile analysis by Auger electron spectroscopy (AES) under ion-sputtering and transmission electron microscopy (TEM). As indicated by electron microscopy the alloy samples treated under CO+Ar at low temperature and low pressure (i.e. 550 ?C and 1 bar) showed a thick layer of surface carbon deposits. The amount of carbon formed on the surface decreases however with the exposure temperature and this requires further investigation in view of the infinite carbon activity and presumed kinetic control under such conditions. Existence of carbon formation could so far not be confirmed under the syngas mixture irrespective of the exposure temperature and pressure and this is in partial contrast to our previous investigations of Inconel 601. Further detailed characterization will be presented and discussed in view of these initial findings.

Key words: metal dusting corrosion, SEM, TEM, Auger depth profile analysis, Raman spectroscopy

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