FIRST-PRINCIPLES ATOMIC CLUSTER STUDY OF BORON INTERACTIONS IN NI3AL

First-principles atomic cluster calculations have been carried out in the local density approximation to understand the segregation behavior and strengthening effects of boron in Ni3Al. The binding energy of bo ron is calculated in lattice fragment clusters representing the perfec t crystal, as well as various defect sites. The agreement between tren ds in energetics determined for small clusters and periodic supercells indicates the dominant role of boron's interaction with nearest-neigh bors of the host. The stereochemical factor underlying boron's prefere ntial bonding to nickel atoms in four-fold planar coordination (i.e., sp(3) hybridization) suggests a mechanism for the baron-effect in Ni3A l: increased cohesion provides a driving force for B segregation to op en sites, such as at Ni-enriched grain boundary sites, and the strengt hening is a result of strong localized Ni-B covalent bond formation. ( C) 1997 American Institute of Physics.