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Formation of corrosion pockets in FeNiCrAl at high temperatures investigated by 3D FIB‐SEM tomography
Author(s) -
Jahns Katrin,
Krupp Ulrich,
Sundell Gustav,
Geers Christine
Publication year - 2020
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.201911386
Subject(s) - chromia , alloy , materials science , corrosion , nitride , metallurgy , nitriding , void (composites) , high temperature corrosion , scanning electron microscope , carbide , oxide , atom probe , chromium , aluminium , focused ion beam , ion , composite material , layer (electronics) , chemistry , organic chemistry
A recently published study of high temperature nitridation of iron chromium aluminum alloys (FeCrAl) at 900°C in N 2 –H 2 has redundantly shown the formation of locally confined corrosion pockets reaching several microns into the alloy. These nitrided pockets form underneath chromia islands laterally surrounded by the otherwise protective alumina scale. Chromia renders a nitrogen‐permeable defect under the given conditions and the presence of aluminum in the alloy. In light of these findings on FeCrAl, a focused ion beam–scanning electron microscope tomography study has been undertaken on an equally nitrided FeNiCrAl sample to characterize its nitridation corrosion features chemically and morphologically. The alloy is strengthened by a high number of chromium carbide precipitates, which are also preferential chromia formation sites. Besides the confirmation of the complete encapsulation of the corrosion pocket from the alloy by a closed and dense aluminum nitride rim, very large voids have been found in the said pockets. Furthermore, metallic particles comprising nickel and iron are deposited on top of the outer oxide scale above such void regions.