The effects of boron and hydrogen on the embrittlement of polycrystalline Ni₃Al

The discrete-variational method within the framework of density functional theory is used to study the effects of both boron and hydrogen on the embrittlement of polycrystalline Ni₃Al. The calculated results show that there are strong repulsive interaction between the boron and the hydrogen atoms, if they occupy the nearest interstitial sites, respectively, in the Ni₃Al grain boundaries. It indicates that the boron atoms inhibit the diffusion of hydrogen atoms along the grain boundary. It may be the main reason why boron can suppress the moisture induced hydrogen embrittlement. Our results also show that the attractive interactions between boron and some substrate atoms are weakened, but the attractive interactions between boron and other substrate atoms are enhanced, when hydrogen atoms are forced into the grain boundary and occupy the nearest interstitial sites to boron atoms. As a result, the bonding states are polarized in the local region of the grain boundary. It may suppress the movement of slips across the grain boundary. Furthermore, the weakening effects of hydrogen to the grain boundary are hardly affected by the boron atoms, even though they are very near to each other. It can be concluded that hydrogen embrittlement takes place when the boron-doped polycrystalline Ni₃Al are charged with hydrogen.