This is the second of two papers that present a theoretical analysis of the phenomenon of hydrogen embrittlement of $\alpha$-Fe. We make contact between the thermodynamic-kinetic continuum and cohesive zone models and the quantum-mechanical magnetic tight-binding approximation to interatomic forces. We are able to solve a coupled set of equations using quantum mechanically obtained atomistic data to follow the decohesion process in time as traction is applied to a hydrogen charged crystal and decohesion occurs between two (111) crystal planes. This scheme will be readily extended from transgranular to intergranular failure, although the complexities of the trapping sites in the cohesive zone associated with a grain boundary will greatly complicate the calculation of the configurational energy. Hydrogen-enhanced decohesion postulated widely in the field has not yet been demonstrated experimentally, although our calculations find a reduction in the ideal cohesive strength as a result of dissolved hydrogen in $\alpha$-Fe from 30 to 22 GPa. Because of the well-known steep and nonlinear relation between plastic and ideal elastic work of fracture, this represents a very significant reduction in toughness as a result of a hydrogen concentration of less than ten atomic parts per million.

• Received 24 April 2017
• Revised 14 June 2017

DOI:https://doi.org/10.1103/PhysRevMaterials.1.033603