Segregation energy of the hydrogen at Ni Σ3 grain boundaries: some implications of the atomic volume and the interstitial self-stress

Atomistic simulations performed for the hydrogen segregation in different Ni Sigma 3 < 110 > tilt grain boundaries (GBs), including symmetrical and asymmetrical configurations, highlight a decreasing functional relationship between the segregation energy and the atomic volume of the GB interstitial site. The analysis of the local deformations around the hydrogen atoms showed that this relationship is not depending on the geometric form of the GB interstitial sites. For small contents of the volume change, a linear correlation was found between the segregation energy of the hydrogen solutes and the volume occupancy of the GB trapping sites. However, when interstitial volumes reach a certain critical value this proportionality presents some limits, especially for GB trapping sites that undergo considerable volume distortions. A general thermo-mechanical framework based on the atomic self-stress calculations is stated to understand locally the connection between the volume occupancy and the elastic relaxed energy from the insertion of hydrogen interstitials in Sigma 3 grain boundaries.