THE BONDING FEATURES AND ENVIRONMENTAL EMBRITTLEMENT OF LL(2) INTERMETALLIC COMPOUNDS

The discrete variational X alpha method (DV X alpha) was applied to ca lculate the bond order and charge transfer of L1(2) ordered Ni(3)X (X= Si, Al, Fe) compounds. We found that there is minor charge transfer be tween the constituent atoms, and X atoms lose some charge. The positiv ely charged X atoms, which we call the reactive centers, bond with the oxygen atoms carrying some negative charge due to electrostatic force . A reaction driving force is proposed and analyzed. We apply the diff erence of the bonding capacity of X atoms in the bulk crystal and at t he surface to predict the tendency of the generation of atomic hydroge n, which is considered the fundamental reason for environmental embrit tlement. The possibility of hydrogen generation is in the order of Ni3 Si > Ni3Al > Ni3Fe.