- Abstract Wetting behavior and the interface reaction in the Y 2 O 3/(Cu–Al) system were investigated at 1423 K. A contact angle of about 130° was measured in the Y 2 O 3/Cu system. Aluminum addition to copper improves wetting and the transition from non-wetting to wetting (θ≤ 90°) was observed for the alloy with 50 at.% Al. The microstructure examination of the interface indicates that Al reacts with yttria, yttrium dissolves in the melt and a crater of AlYO 3 is formed at the substrate. The interface interaction in the Y 2 O 3/(Cu–Al) system is in a good agreement with the results of a thermodynamic analysis in the Y–Al–Cu–O system. The crater depth and the macroscopic final contact angles are correlated with the Y and Al activities in the melt.