Impurity effects on adhesion at an interface between NiAl and Mo

Fully self-consistent (LDA) density functional calculations have been performed to obtain the ideal adhesion energy and peak interfacial stress for rigid fracture of an [001] interface between NiAl and Mo with and without interfacial impurities. These calculations shed light on interfaces in NiAl-Mo eutectic composites in which [001] interfaces between NiAl (CsCl structure) and Mo (b.c.c.) are prominent. In all cases impurities reduce the adhesion energy, from 3.3 J/m² for the clean interface to 2.4, 1.5, and 1.4 J/m² for C, O, and S impurities, respectively. Interestingly, however, C increases (40.0 GPa), while O (26.0 GPa) and S (18.0 GPa) decrease the peak interfacial stress from that for the clean interface (37.0 GPa). The Harris functional was also tested, and it was found that the ordering of adhesion energies and peak interfacial stresses were the same as for the fully self-consistent results, but errors in the magnitudes were significant. Misfit dislocations play an important role and are estimated to reduce the adhesion energy of the clean interface by an amount of the order of 10%.