Environmental embrittlement caused by hydrogen for intermetallic compounds: Preliminary model of ductility reduction

The reduction of fracture elongation caused by environmental embrittlement has been dealt with for intermetallic alloys as follows. The fresh surface that is formed by plastic deformation increases with an increase in tensile deformation, and hydrogen permeating through the fresh surface into the specimen increases and embrittles its surface layer. Thus, a microcrack nucleates at the surface layer. The crack propagates unstably through the specimen because of the low fracture toughness of intermetallic alloys, resulting in the fracture of the specimen. Hydrogen permeating into the specimen increases with the increasing fresh surface area and increasing period of exposure to the environment. The dependence of fracture elongation on strain rate and hydrogen pressure has been described by a phenomenological and preliminary model, which has been proposed according to the consideration mentioned previously. The experimental data which were reported for intermetallic alloys have been compared to the phenomenological model.