The connection between ab initio calculations and interface adhesion measurements on metal/oxide systems: Ni/Al2O3 and Cu/Al2O3

The Ni/Al2O3 and Cu/Al2O3 interfaces have been examined by atomistic, first-principles computations. Relationships have been established with such metallurgical variables as the activity of aluminum and the partial pressure of oxygen. The calculations reveal that the interfaces could be either stoichiometric, or Al-rich, or O-rich, depending on the Al activity. The results are amenable to comparison with available sessile drop and fracture measurements. For conditions applicable to sessile drop experiments performed with Ni(Al) or Cu(Al), the calculations reveal that, as the Al activity increases, initially the work of adhesion increases, reaches a maximum, and finally decreases to that for pure Al. This trend is consistent with the known measurements. Interfaces generated by diffusion-bonding with ‘pure’ Ni or Cu are predicted to be O-rich, with a large work of separation, Wsep. The implication is that the separation process induces substantial plastic dissipation in the metal, consistent with the high interface toughness. For interfaces formed through Al2O3 growth on Ni(Al) alloys, the interface is predicted to be Al terminated, with Wsep several times smaller than for either bulk Ni or Al2O3. This reduction is in accordance with observations that these interfaces fail in a brittle manner with no noticeable plasticity.