The discrete-variational method within the framework of density-functional theory is used to study the effect of hydrogen on the embrittlement of polycrystalline ${\mathrm{Ni}}_3\mathrm{Al}$. The calculated results of impurity formation energy show that hydrogen atoms prefer to segregate at the grain boundaries, and occupy the Ni-rich interstitial holes in the polycrystalline ${\mathrm{Ni}}_3\mathrm{Al}$. The equilibrium positions of H atoms are near a certain atom instead of the center of these holes. The calculated results of interatomic energies reveal that the bonding strength of host atoms, which are near hydrogen atoms, are reduced evidently by the presence of hydrogen. The overall effect of H is to decrease the cohesive strength of ${\mathrm{Ni}}_3\mathrm{Al}$ grain boundaries and make intergranular fracture easier.

• Received 27 January 1997

DOI:https://doi.org/10.1103/PhysRevB.57.289