Effect of aluminum content on environmental embrittlement in binary iron-aluminum alloys

Abstract

Interest in iron-aluminum alloys has existed for the last sixty years, on account of their attractive properties including low density, excellent oxidation resistance, and conservation of strategic elements. This paper reports that recent investigations have focused on the ordered Fe{sub 3}Al-based alloys containing 15.9 wt % Al, and FeAl-based alloys containing about 22 wt % Al. However, the poor room-temperature ductility and sharp drop in strength at temperatures above 600{degrees} C in these alloys have been major deterrents to their acceptance in structural applications. In particular, the poor room-temperature ductility has been shown to be the result of environmental embrittlement in the presence of water vapor; ductility as measured by total elongation in heat-treated tensile specimens has been shown to be significantly higher in oil-quenched samples and samples tested in vacuum than in air-cooled samples tested in air. The increase in ductility in samples tested in vacuum has been assumed to be due to the absence of water vapor in the test environment, essential to the formation of atomic hydrogen involved in the embrittlement mechanism. The increase in ductility in oil-quenched specimens may be assumed to be due to the presence of a film of oil on the specimen surfacemore » that serves to provide a barrier to water vapor in air and, thus, prevent the generation of hydrogen on the surface from the reaction of aluminum in the alloy with water vapor.« less