Application of molecular dynamics to the study of hydrogen embrittlement in Ni-Cr-Fe alloys.

Abstract

Molecular dynamics and the embedded-atom method (EAM) have been applied to the study of intergranular hydrogen embrittlement in Ni-based alloys. A new technique was developed for constructing EAM functions from experimental data on binary systems. The technique allows one to express experimental quantities of the binary alloy in terms of EAM functions for each constituent element, and then to fine tune the parameters for one of the elements to fit the experimental data. The method was used to construct EAM functions for H and for the Ni-Cr-Fe system. The functions were then used in dynamic simulations of grain boundaries to study the effect of H on their stress-strain--fracture behavior. The simulations suggest that hydrogen-embrittlement susceptibility is strongly linked to grain-boundary structure. Boundaries possessing large gaps and structural irregularities are affected adversely, while boundaries lacking these defects are resistant to embrittlement. The results of the study are discussed in terms of the influence of the simulation methodology on the observed grain-boundary fracture behavior of Ni-Cr-Fe alloys as a function of boundary type, boundary structure, and hydrogen content.