RELATIONSHIP BETWEEN BONDING CHARACTERISTICS AND MECHANICAL-PROPERTIES OF L1(2) INTERMETALLICS

The bonding characteristics of A(3)B L1(2) intermetallics have been st udied by the discrete variational X(alpha) cluster method. Two concept s, i.e. similarity of bonding strength and delocalization of bonding e lectrons, are introduced to explain the ductility or brittleness of th e materials. The analysis of bonding characteristics shows that the st rength of the A-A bond is similar to that of the A-B bond in A(3)B L1( 2) intermetallics, and the delocalized degree of bonding electrons is different between the ductile and brittle intermetallics. This is a do minant factor in governing the ductile/brittle behavior of the materia ls. Environmental embrittlement in some intermetallics is related to t he reactive centers in grain boundaries, which is due to the direction al bonding and a small amount of charge transfer, and the reactive cen ters weaken the ability against the attack of the environmental specie s. The effect of stoichiometry on ductility contributes to the degree of delocalized bonding electrons. Mechanical strength of the materials is correlated with the covalent bond strength.