  Atomistic calculations were carried out to investigate the mechanical
properties of Pd crystals as a combined function of structural defects,
hydrogen concentration and high temperature. These factors are found to
individually induce degradation in the mechanical strength of Pd in a
monotonous manner. In addition, defects such as vacancies and grain boundaries
could provide a driving force for hydrogen segregation, thus enhance the
tendency for their trapping. The simulations show that hydrogen maintains the
highest localization at grain boundaries at ambient temperatures. This finding
correlates well with the experimental observation that hydrogen embrittlement
is more frequently observed around room temperature. The strength-limiting
mechanism of mechanical failures induced by hydrogen is also discussed, which
supports the hydrogen-enhanced localized plasticity theorem.
