The tribocorrosion behaviour of overlay welded Ni-Cr 625 alloy sliding against alumina in 0.5 M H2SO4 and 0.5 M HNO3 solutions under potentiostatic conditions was investigated. The passivation of the samples in the two electrolytes at different potentials ( -1.5, -0.3 and +0.3 V-MSE) was studied by means of potentiodynamic polarization curves and XPS. The tribocorrosion behaviour of the alloy in sulphuric acid was similar to the behaviour of stainless steels found in other studies, with much lower wear at cathodic potential compared to passive conditions. However, the behaviour in nitric acid was highly influenced by the reduction of nitric acid at the electrode-electrolyte interface. This reaction leads to the oxidation of the alloy even at cathodic potential. This feature influenced the tribocorrosion properties of the alloy in nitric acid, the wear rate at cathodic potential being in the same range as at passive potentials. (C) 2009 Elsevier Ltd. All rights reserved.