A Critical Reexamination of the Peierls-Nabarro Model

The first principles discrete variational method (DVM) is used to investigate the alloying effect of Fe, Al and B on the environmental embrittlement of Ll2Co3Ti alloy. The values of the binding energy, Fermi energy, bond order, directionality of bonding and density of states are calculated and analyzed. By comparing the results of Fe, Al and B additions with those of the undoped Co3Ti alloy, we can examine the effects of alloying. The present calculations indicate that the addition of Fe and Al creates a more homogeneous electronic distribution at grain boundary and makes the grain boundary cluster less reactive with water. The effect of B on the bonding features is also discussed, the anti-bonding Co3B may suggest that B has little effect on improving the ductility of Co3Ti alloy.