WETTING AND ADHESION OF NI-AL ALLOYS ON ALPHA-AL2O3 SINGLE-CRYSTALS

The effect of Al additions on the wetting and adhesion of Ni on an alpha-Al2O3 single crystal was studied. Contact angles were measured by the sessile drop technique under vacuum or in He atmosphere. The morphological and chemical features of metal-vapour and metal-oxide interfaces were determined by scanning electron microscope (SEM), microprobe analysis and profilometry. The work of adhesion of Ni-Al alloys on Al2O3 substrates was significantly higher than for pure Ni and Al components. This result was explained by co-operative adsorption of aluminium and oxygen atoms at the Ni-Al2O3 interface. The influence of oxidation of the alloy on wetting and bonding is also discussed.