Influence of trap connectivity on H diffusion: Vacancy trapping

A model is given for the effective diffusion of interstitial solutes in the presence of traps. It goes beyond Oriani's by taking into account, in a simple way, the connectivity between interstitial trap sites. It shows, in particular, that the typical dimension of a network of trap sites, connected by low barriers, appears squared in the diffusion coefficient. Therefore, a large precipitate can be inefficient if it offers a fast diffusion path, even if each individual trap site is deep. The model is illustrated in the case of hydrogen trapping at vacancies in Ni, using ab initio calculations for migration barriers and Kinetic Monte Carlo for validation. Trapping/detrapping kinetic parameters for “Thermal Desorption Spectra” analysis are also given.

This article originally appeared in Acta Materialia, 103, 2016, Pages 334-340.