Authors: Pint, B.A.; Zhang, Y.; Tortorelli, P.F.; Haynes, J.A.; Wright, I.G.

Source: Materials at High Temperatures, Volume 18, Number 3, August 2001 , pp. 185-192(8)

Publisher: Science Reviews 2000 Ltd

Abstract:

Chemical vapor deposited (CVD) Fe-Al coatings are being investigated to address fundamental issues concerning aluminide coating performance and lifetime. By using a well-controlled laboratory CVD procedure, the coatings are uniform in composition, purity and microstructure. A typical ferritic steel, Fe-9Cr-1Mo, and an austenitic stainless steel, 304L (nominally Fe-18Cr-9Ni), were coated to examine differences in the two types of substrates. For both substrates, the as-deposited coating consisted of a thin (<5 μm), Al-rich layer above a thicker (30-50 μm), lower Al content layer. To follow-up on initial results, which showed good coating performance in air+10vol.%H₂O and H₂S-H₂O-H₂-Ar, cyclic tests were performed in both environments at 800°C and more detailed characterization of the isothermally exposed coatings was conducted. During 2-5, 25 h cycles at 800°C in H₂S-H₂O-H₂-Ar, CVD coatings on both substrates showed progressively more attack during each cycle. However, in 1h cycles at 800°C in air+10vol.%H₂O, the coatings showed excellent performance, similar to cast Fe-(15-20at.%)Al specimens. The uncoated alloys were significantly attacked during all of these tests. Thermal expansion measurements show Al additions up to 20at.% have little effect on the mean expansion of ferritic alloys but the higher thermal expansion of austenitic steels may be a better match with Fe₃Al coatings.

Keywords: chemical vapour deposited Fe-Al coatings

Document Type: Research article

DOI: http://dx.doi.org/10.3184/096034001783640559

Affiliations: 1: Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6156, USA

Publication date: 2001-08-15

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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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