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Title: The effects of molybdenum on the high-temperature oxidation resistance of thin foils of Fe-20Cr-5Al at very high temperatures

Abstract

Thin foils of Fe-20Cr-5Al alloys are susceptible to breakaway oxidation once the aluminum content of the substrate has fallen below some critical value. The combined addition of 0.1 wt.% lanthanum and 0, 1, or 2 wt% molybdenum has a beneficial effect on the high-temperature oxidation of such foils. Lanthanum has the well-known reactive-element effect on adhesion of the protective alumina scale, thereby increasing the time to onset of breakaway oxidation, while, for alloys containing molybdenum, breakaway oxide spreads relatively slowly over the specimen in comparison to alloys that contain no molybdenum. In particular, molybdenum-containing alloys are able to develop a protective Cr{sub 2}O{sub 3} layer at the breakaway oxide-substrate interface. Conversely, molybdenum-free alloys form an internal-oxide zone in the substrate adjacent to this interface, rather than a Cr{sub 2}O{sub 3} layer, so breakaway oxide spreads rapidly. A martensitic phase is observed in the substrate adjacent to the breakaway oxide formed on Fe-20Cr-5Al-La specimens, which means that the {alpha}-phase has transferred to the {gamma}-phase at the temperature of the oxidation test (1,150 C). Conversely, {alpha}-phase is retained in the molybdenum-containing alloy, even after breakaway takes place, since molybdenum, which is a strong ferrite former, is enriched in the alloy adjacent tomore » areas of breakaway oxide. The diffusion rate of chromium is slower in the {gamma} than in the {alpha}-phase so a continuous chromium-rich oxide layer, which is effective in inhibiting breakaway oxide from spreading, cannot be established at the breakaway oxide-substrate interface for the molybdenum-free alloys.« less

Authors:
;
Publication Date:
Research Org.:
UMIST, Corrosion and Protection Center, Manchester (GB)
OSTI Identifier:
20050533
Resource Type:
Journal Article
Journal Name:
Oxidation of Metals
Additional Journal Information:
Journal Volume: 53; Journal Issue: 5-6; Other Information: PBD: Jun 2000; Journal ID: ISSN 0030-770X
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; OXIDATION; IRON ALLOYS; CHROMIUM ALLOYS; ALUMINIUM ALLOYS; FOILS; MOLYBDENUM ADDITIONS; TEMPERATURE RANGE 1000-4000 K; INTERFACES; KINETICS

Citation Formats

Hiramatsu, N., and Stott, F.H. The effects of molybdenum on the high-temperature oxidation resistance of thin foils of Fe-20Cr-5Al at very high temperatures. United States: N. p., 2000. Web. doi:10.1023/A:1004689211302.
Hiramatsu, N., & Stott, F.H. The effects of molybdenum on the high-temperature oxidation resistance of thin foils of Fe-20Cr-5Al at very high temperatures. United States. doi:10.1023/A:1004689211302.
Hiramatsu, N., and Stott, F.H. Thu . "The effects of molybdenum on the high-temperature oxidation resistance of thin foils of Fe-20Cr-5Al at very high temperatures". United States. doi:10.1023/A:1004689211302.
@article{osti_20050533,
title = {The effects of molybdenum on the high-temperature oxidation resistance of thin foils of Fe-20Cr-5Al at very high temperatures},
author = {Hiramatsu, N. and Stott, F.H.},
abstractNote = {Thin foils of Fe-20Cr-5Al alloys are susceptible to breakaway oxidation once the aluminum content of the substrate has fallen below some critical value. The combined addition of 0.1 wt.% lanthanum and 0, 1, or 2 wt% molybdenum has a beneficial effect on the high-temperature oxidation of such foils. Lanthanum has the well-known reactive-element effect on adhesion of the protective alumina scale, thereby increasing the time to onset of breakaway oxidation, while, for alloys containing molybdenum, breakaway oxide spreads relatively slowly over the specimen in comparison to alloys that contain no molybdenum. In particular, molybdenum-containing alloys are able to develop a protective Cr{sub 2}O{sub 3} layer at the breakaway oxide-substrate interface. Conversely, molybdenum-free alloys form an internal-oxide zone in the substrate adjacent to this interface, rather than a Cr{sub 2}O{sub 3} layer, so breakaway oxide spreads rapidly. A martensitic phase is observed in the substrate adjacent to the breakaway oxide formed on Fe-20Cr-5Al-La specimens, which means that the {alpha}-phase has transferred to the {gamma}-phase at the temperature of the oxidation test (1,150 C). Conversely, {alpha}-phase is retained in the molybdenum-containing alloy, even after breakaway takes place, since molybdenum, which is a strong ferrite former, is enriched in the alloy adjacent to areas of breakaway oxide. The diffusion rate of chromium is slower in the {gamma} than in the {alpha}-phase so a continuous chromium-rich oxide layer, which is effective in inhibiting breakaway oxide from spreading, cannot be established at the breakaway oxide-substrate interface for the molybdenum-free alloys.},
doi = {10.1023/A:1004689211302},
journal = {Oxidation of Metals},
issn = {0030-770X},
number = 5-6,
volume = 53,
place = {United States},
year = {2000},
month = {6}
}