Influence of the micro-addition of Mo on glass forming ability and corrosion resistance of Cu-based bulk metallic glasses

(Cu47Zr11Ti34Ni8)100-xMo x bulk metallic glasses (BMGs) with x = 0, 1 and 2 at.% and a bulk metallic glass matrix composite with x = 5 at.% were successfully prepared by water-cooled copper mold casting. The effect of the addition of a small amount of Mo on the glass forming ability (GFA), thermal properties of the base alloy (i.e. x = 0) were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analyzer (DTA). It is found that the addition of appropriate amount of Mo can enhance the GFA of the Cu-based BMG, as indicated by the increase in the reduced glass transition temperature T rg (=T g/T l) and the parameter γ (=T x/(T g + T l)) with the increase of Mo. On the other hand, the corrosion resistance of the Cu-based BMGs with different Mo contents was examined by electrochemical polarization and weight loss measurement in 1 mol/L H2SO4 and 1 mol/L NaOH solutions, respectively. It is found that the corrosion resistance of Cu-based BMGs increased with increasing Mo content with the lowest corrosion rate of (0.9 ± 0.2) x 10-3 mm/year in 1 mol/L H2SO4 solution and (0.3 ± 0.1) x 10-3 mm/year in 1 mol/L NaOH solution, respectively, for the BMG containing 2 at.% Mo. X-ray photoelectron spectroscopy (XPS) results revealed that the improvement of corrosion resistance of Cu-based BMG containing appropriate amount of Mo originated from the enrichment of ZrO2 and TiO2, but depletion in Cu- or Ni-oxides in the passive films formed during electrochemical polarization. Finally, the galvanostatic-step measurement was performed to investigate the kinetics of the formation of passive films on the BMG surfaces. It is demonstrated that the addition of an appropriate amount of Mo can effectively improve the stability and uniformity of the passive film. The role of Mo addition on the glass forming ability and corrosion behavior is discussed