Journal Article

FZJ-2015-07475

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Sigma-Phase Formation in High Chromium Ferritic Steels at 650°C

Niewolak, L. (Corresponding author)FZJ* ; Garcia-Fresnillo, L. ; Meier, G. H. ; Quadakkers, W. J.FZJ*

2015
Elsevier Lausanne

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Please use a persistent id in citations: doi:10.1016/j.jallcom.2015.03.076

Abstract: A binary Fe–30 wt.%Cr alloy and corresponding ternary alloys containing manganese, molybdenum or tungsten were studied with respect to σ-phase formation at 650 °C. Although even after 3000 h exposure complete equilibration was not attained, the presence of tungsten and especially molybdenum was found to promote σ-phase formation. More extensive σ-phase formation was observed in the tungsten and especially in the molybdenum-containing alloys than in the binary and manganese-containing alloy. Apparently the bulk free energy decrease driving the nucleation of σ-phase is substantially larger when tungsten or molybdenum are present in the alloy.The presence of a nickel layer, to simulate the contact between ferritic steel interconnects and nickel mesh in a Solid Oxide Fuel Cell (SOFC) results in the formation of an austenitic zone and in accelerated formation of a σ-phase rich layer at the ferrite/austenite interface, due to interdiffusion processes. This interface acts as a highly efficient heterogeneity for the nucleation of σ-phase. The nucleation is enhanced by an increased Cr/Fe-ratio at that interface. Several possible modes for the growth of the σ layer were identified but the available experimental data were not sufficient to distinguish among these. The σ-rich layer, which appears to act as an interdiffusion barrier, is thicker in the case of the binary Fe–Cr and the Fe–Cr–Mn alloy than for the molybdenum- or tungsten-rich alloys.The results show that the stability range of σ-phase is larger than indicated by the presently used thermodynamic data bases.

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Contributing Institute(s):

1. Werkstoffstruktur und -eigenschaften (IEK-2)

Research Program(s):

1. 111 - Efficient and Flexible Power Plants (POF3-111) (POF3-111)

Appears in the scientific report 2015

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Database coverage:
; Current Contents - Physical, Chemical and Earth Sciences ; IF < 5 ; JCR ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Thomson Reuters Master Journal List ; Web of Science Core Collection

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