Cathodic hydrogen embrittlement in alloy 718

Room temperature cathodic hydrogen embrittlement in alloy 718 was investigated by means of slow strain rate tensile tests conducted on specimens charged either prior to or during deformation. Tensile tests performed on precharged specimens at strain rates of 5×10−7, 5×10−5 and 5×10−3 s−1 suggest that hydrogen embrittlement is correlated with hydrogen segregation to moving dislocation and transport by these dislocations. Observations of 1 μm planar cleavage microfacets on fracture surfaces of specimens charged either prior to or during deformation support the idea that embrittlement occurs by strong hydrogen–deformation interactions. In light of these results, the role of the cathodic hydrogen produced by the corrosion process inside a crack during stress corrosion cracking is discussed in conjunction with the corrosion enhanced plasticity model, proposed some years ago by one of the authors. It is suggested that hydrogen transport by dislocations and localisation along active slip planes may be the controlling stage of the cracking process.