The effects of boron and hydrogen on the embrittlement of polycrystalline Ni_3Al

摘要

The discrete-variational method within theframework of density functional theory is used to study theeffects of both boron and hydrogen on the embrittlement ofpolycrystalline Ni_3Al. The calculated results show that therearc strong repulsive interaction between the boron and thehydrogen atoms, if they occupy the nearest interstitial sites,respectively, in the Ni_3Al grain boundaries. It indicates that theboron atoms inhibit the diffusion of hydrogen atoms along thegrain boundary. It may be the main reason why boron cansuppress the moisture induced hydrogen embrittlement. Ourresults also show that the attractive interactions between boronand some substrate atoms are weakened, but the attractiveinteractions between boron and other substrate atoms areenhanced, when hydrogen atoms are forced into the grainboundary and occupy the nearest interstitial sites to boron atoms.As a result, the bonding states are polarized in the local regionof the grain boundary. It may suppress the movement of slipsacross the grain boundary. Furthermore, the weakening effectsof hydrogen to the grain boundary are hardly affected by theboron atoms, even though they are very near to each other. It canbe concluded that hydrogen embrittlement takes place when theboron-doped polycrystalline Ni_3Al are charged with hydrogen.