Mechanism of Macroalloying-induced Ductility in Ni_3Al

The bonding characteristics of Ni 3 Al doped with ternary elements has been investigated by means of the discrete variational Xα (DV-Xα) cluster method. From the computations, the addition of ternary element M (M= Pd, Ag, Cu and Co) substituting for the Ni sites leads to the increase of delocalized bonding electrons, and the mechanism of ductilization of Ni 3 Al by doping with M is explained based on the analysis of bonding characteristics. The increase of delocalized bonding electrons lowers the covalent bond directionality and strengthens gram boundary. The difference of strength between M-Al bond and M-Ni bond is an important factor in the effect of alloy stoichiometry on ductility. The larger the difference, the more the sensitivity to the alloy stoichiometry