Authors: Park, Eungyeul; Hüning, Boris; Borodin, Sergiy; Rohwerder, Michael; Spiegel, Michael

Source: Materials at High Temperatures, Volume 22, Numbers 3-4, August 2005 , pp. 567-573(7)

Publisher: Science Reviews 2000 Ltd

Abstract:

In order to understand the initial oxidation of Fe-Cr alloys a single crystal of Fe-15Cr (100) was oxidized at 440°C under controlled oxygen partial pressure in a UHV system and the surface morphology was observed using in situ STM (basic pressure 1×10⁻¹⁰ mbar); in addition, polycrystalline Fe&15Cr was oxidized at 400°C in an IR-furnace in atmospheric air and the morphology was observed using ex situ SEM. The chemistry of the surface oxide layers was studied by XPS.

Preparation of the single crystal in the UHV system did not lead to segregation of Cr to the surface during heating. In situ STM investigation showed that oxidation of Fe-Cr commenced by nucleation of Cr oxide on the surface, due to selective oxidation of Cr. When the Cr at the surface and at the interface was completely consumed by nucleation of Cr oxide, Fe oxidized and covered the initial Cr oxide nuclei, resulting in an Fe oxide layer on the surface. Ex situ experiments showed that initial oxidation of the mechanically prepared polycrystalline alloy depended on the defect distribution in the surface. It started with formation of whisker-type Fe oxides along defects and proceeded with spherical-type nucleation and growth of Fe oxide. In both experiments, the final product on the surface was Fe₂O₃.

Keywords: STM; XPS; Cr; segregation; oxidation

Document Type: Research article

DOI: http://dx.doi.org/10.3184/096034005782744344

Affiliations: 1: Department of Interface Chemistry and Surface Engineering, Max-Planck-Institut für Eisenforschung, D-40237 Düsseldorf, Germany

Publication date: 2005-08-15

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• Materials at High Temperatures serves the needs of those who develop and use materials for high temperature applications. It publishes peer reviewed contributions relating to high temperature applications in the power, chemical, engine, processing and furnace industries.

  The effects of high temperatures on corrosion, fatigue, creep, strength and wear in alloys, intermetallics, ceramics, refractories and composites are covered. Papers dealing with aspects of materials usage including modelling of behaviour and life prediction will be particularly welcome. The journal has a policy of emphasizing practical aspects and authors presenting results from research programmes are encouraged to relate these, if possible, to actual or potential applications.

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