Hydrogen Diffusivity in a Fe 3Al-Based Alloy

Abstract

Many studies of environmental embrittlement have revealed that the active element (Al in aluminides) in intermetallics reacts with moisture in air, resulting in the generation of atomic hydrogen, which penetrates into crack-tip region and causes brittle intergranular or cleavage fracture. In the mean time, the active element can be oxidized as a result of the reaction with water vapor, leading to the formation of an adherent surface oxide film, which makes it more difficult to investigate the hydrogen diffusion in intermetallic compounds. Presumably, this is the reason why the hydrogen diffusivity data for intermetallics are not yet available. Nishimura et al. have found that a Ni{sub 3}Al specimen with columnar grain structure, grown unidirectionally by a floating zone method, exhibited in excess of 50% elongation to fracture in air at room temperature, indicating no environmental embrittlement. A great deal of research has also shown that Fe{sub 3}Al and its related alloys have similar characteristics. The elongation of the incompletely recrystallized Fe{sub 3}Al with an elongated grain shape is 23% in dry oxygen and 12.2% in air, while that of the same material with a completely recrystallized equiaxed grain shape is only 17.5% in dry oxygen and 7.2% in air. Itmore » has been assumed that the effect of morphology of the microstructure on the sensitivity to environmental embrittlement in Fe{sub 3}Al-based alloy may be related to the different hydrogen diffusivity. The purpose of this study is to investigate the hydrogen diffusivity in a Fe{sub 3}Al-based alloy with different grain shapes or sizes.« less