ADHESION IN NIAL-CR FROM FIRST-PRINCIPLES

Fully self-consistent all-electron density functional calculations hav e been performed to obtain the full adhesion curves for the systems Ni Al, Cr, and NiAl-Cr. We find that the work of adhesion for Cr is large r than that for NiAl and for the interface between these two materials the work of adhesion is intermediate. We find that NiAl at the NiAl-C r interface is Ni-terminated. Electronic charge density distributions indicate that the bonding is largely metallic with a discernible coval ent character. The interfacial bonding is due largely to the Ni and Cr d electrons while in NiAl the bonding results from sp-d hybridization . Estimates of segregation effects suggest a reduction of the work of adhesion for the interface by roughly 20%. Comparisons between our cal culated ideal work of adhesion and fracture toughness measurements ind icate that significant crack-tip plasticity is associated with the bri ttle fracture mechanism of NiAl. Our results are consistent with previ ous electronic structure calculations and measurements on NiAl and fra cture mechanisms observed for NiAl-Cr composites.