Abstract
Iron aluminides based on Fe3Al are of interest as structural materials because of their excellent corrosion resistance in many environments. However, studies have shown that one of the major causes of low room temperature tensile ductility, which so far has limited the use of these alloys, is an environmental reaction involving aluminum in the presence of water vapor. During this reaction, atomic hydrogen is released, moves into the sample ahead of the crack tip during stressing, and causes failure before the true ultimate tensile strength of the material is reached. This reaction is reduced significantly by testing in oxygen or vacuum. In the present study, an Fe3Al-based alloy was tensile tested as a function of the level of water vapor in the test environment, from a vacuum of 10−4 Pa to a water vapor partial pressure of 1330 Pa. The results show that a water vapor level of as low as 133 Pa (1 torr) can result in significant embrittlement. The fracture mode remains transgranular cleavage, but the scale of the cleavage facets changes with the water vapor level.
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Acknowledgements
The authors would like to thank J. A. Horton, Jr. and P. J. Maziasz for reviewing the manuscript. Research sponsored by the U.S. Department of Energy, Fossil Energy AR&TD Materials Program under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc.
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Mckamey, C.G., Lee, E.H. Measurement of the Critical Level of Moisture for Initiation of Water-Vapor-Induced Environmental Embrittlement in an Fe3Al-Based Alloy. MRS Online Proceedings Library 288, 983–988 (1992). https://doi.org/10.1557/PROC-288-983
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DOI: https://doi.org/10.1557/PROC-288-983