On the mechanism of hydrogen-environment embrittlement of iron- and nickel-base alloys

Abstract

The literature on internal hydrogen embrittlement and hydrogen-environment embrittlement of iron-base and nickel-base alloys, with emphasis on the mechanisms by which embrittlement occurs, is reviewed. In general, there is little correlation between susceptibilities of various metals to internal hydrogen embrittlement and hydrogen-environment embrittlement.Hydrogen-environment embrittlement involves crack initiation at the metal surface while internal hydrogen embrittlement involves crack initiation inside the metal. Two surface-dependent mechanisms for hydrogen-environment embrittlement are proposed. One is based upon the heat of adsorption of hydrogen, which decreases the strain energy needed to initiate a crack. The second mechanism is the absorption of hydrogen into the surface, where it lowers the surface ductility, possibly by inhibition of dislocation generation at the surface, or by increasing the lattice friction stress for dissociation motion at the surface.