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 alp ha-Al2O3 single crystal was studied. Contact angles were measured by t he sessile drop technique under vacuum or in He atmosphere. The morpho logical and chemical features of metal-vapour and metal-oxide interfac es were determined by scanning electron microscope (SEM), microprobe a nalysis and profilometry. The work of adhesion of Ni-Al alloys on Al2O 3 substrates was significantly higher than for pure Ni and Al componen ts. 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.