Corrosion behavior of melt-spun Mg 65Ni 20Nd 15 and Mg 65Cu 25Y 10 metallic glasses

Abstract

The corrosion characteristics of melt-spun metallic glasses Mg–Ni and Mg–Cu with and without Nd and Y addition in 0.01 M NaCl (pH 12) electrolyte were studied by hydrogen evolution testing and potentiodynamic polarization methods. Both the dissolution rate and corrosion current density of ternary Mg 65Ni 20Nd 15 and Mg 65Cu 25Y 10 were found to be lower than those of binary Mg 82Ni 18 and Mg 79Cu 21 alloys. Potentiostatically formed surface layers on Mg 65Ni 20Nd 15 and Mg 65Cu 25Y 10 were characterized with depth profile X-ray photoelectron spectroscopy (DP-XPS). The native and breakdown films were also characterized for comparison. For both Mg 65Ni 20Nd 15 and Mg 65Cu 25Y 10, it revealed that both the surface products of the native and passive films consisted of oxide species of all metallic elements and the depth distributions of oxide species were same: MgO was enriched at the outer region while NiO or CuO was depleted throughout the whole layer; Nd 2O 3 and Y 2O 3 were depleted in the outer region and then enriched in the inner region. The breakdown films consisted of the mixture of oxides and hydroxides, mainly of Mg(OH) 2. The incorporation of NiO and Nd 2O 3 (for Mg 65Ni 20Nd 15) and CuO and Y 2O 3 (for Mg 65Cu 25Y 10), especially the rare earth (RE) oxides, in the passive layers has a beneficial effect to improve the corrosion resistance while their hydroxidation leads to the passivity breakdown.