Chemical aspects of environmental embrittlement in iron and nickel aluminides

This paper briefly summarizes our work on chemical aspects of environmental embrittlement in iron aluminides (Fe₃Al and FeAl) and nickel aluminide (Ni₃Al). The aluminides are intrinsically ductile at ambient temperatures, and their low ductilities are essentially caused by environmental embrittlement involving the reaction of moisture in air with reactive elements in intermetallics and the generation of hydrogen at crack tips. It has been observed that moisture-induced environmental embrittlement promotes brittle grain-boundary fracture in fcc-ordered Ni₃Al and cleavage fracture in bcc-ordered iron aluminides. The worst embrittlement usually occurs around ambient temperatures, which is explained quantitatively by a thermodynamic model based on consideration of a kinetic effect at lower temperatures and an equilibrium effect at higher temperatures.