Discussion of some recent literature on hydrogen-embrittlement mechanisms: addressing common misunderstandings

Abstract

Abstract There have been several reviews and numerous papers on hydrogen-embrittlement phenomena and mechanisms in the past few years, but long-standing controversies regarding mechanisms of embrittlement (when hydride phases are not involved) are no closer to being resolved despite all the recent research. These controversies have arisen partly because there have been significant misunderstandings of some of the proposed mechanisms, and some misinterpretation of experimental observations. There has also been a lack of consideration of all the evidence, with some researchers ignoring observations that do not fit their favoured hypothesis. Some recent reviews and papers illustrating the above points are discussed in the present paper, although a comprehensive coverage is not attempted. It is concluded that the adsorption-induced dislocation-emission/void-coalescence mechanism predominates for cleavage-like and intergranular fracture modes that exhibit microscale or nanoscale dimples. Hydrogen-enhanced decohesion, hydrogen-enhanced localised plasticity, and vacancy-based mechanisms may play secondary roles for such fracture modes and could be more important in other cases.