Structure and energetics of clean and hydrogenated Ni surfaces and symmetrical tilt grain boundaries using the embedded-atom method

Abstract

Multilayer relaxations, surface/interface energies, and hydrogen binding sites and energies were systematically studied using the embedded-atom method, for a series of the clean and hydrogenated Ni surfaces and symmetrical tilt Ni grain boundaries. The hydrogen binding energies were in the range of 2.7--2.9 eV at the surface sites while 2.1--2.6 eV at the grain-boundary sites, both being larger than at the fcc crystal interior site, 2.1 eV. These data are consistent with the conclusions from ab initio calculations that intergranular embrittlement is seen by hydrogen segregation at the Ni grain boundaries. It was found that multilayer relaxation of Ni plays a key role in trapping hydrogen at the grain boundaries.