The electrochemical properties of as-cast Zr56Cu19Ni11Al9Nb5 metallic glass and samples annealed at different temperatures were investigated using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS) in phosphate buffer saline (PBS) solution. It was shown that passivation occurred for the as-cast sample and the samples annealed at 623-823 K, indicating good corrosion resistance. At higher annealing temperature, the corrosion resistance first increased, and then decreased. The sample annealed at 823 K exhibited the best corrosion resistance, with high spontaneous corrosion potential Ecorr at -0.045 VSCE, small corrosion current density icorr at 1.549 × 10-5 A·cm-2, high pitting potential Epit at 0.165 VSCE, the largest arc radius, and the largest sum of Rf and Rct at 5909 Ω·cm2. For the sample annealed at 923 K, passivation did not occur, with low Ecorr at -0.075 VSCE, large icorr at 1.879 × 10-5 A·cm-2, the smallest arc radius, and the smallest sum of Rf and Rct at 2173 Ω·cm2, which suggested the worst corrosion resistance. Proper annealing temperature led to improved corrosion resistance due to structural relaxation and better stability of the passivation film, however, if the annealing temperature was too high, the corrosion resistance deteriorated due to the chemical inhomogeneity between the crystals and the amorphous matrix. Optical microscopy and scanning electron microscopy (SEM) examinations indicated that localized corrosion occurred. Results of energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) illustrated that the main corrosion products were ZrO2, CuO, Cu2O, Ni(OH)2, Al2O3, and Nb2O5.
Keywords: annealing; corrosion; electrochemical properties; metallic glass; phosphate buffer saline (PBS) solution.