Effect of Annealing Temperature on Electrochemical Properties of Zr 56 Cu 19 Ni 11 Al 9 Nb 5 in PBS Solution.

The electrochemical properties of as-cast ZrCuNiAlNb 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 E at -0.045 V, small corrosion current density i at 1.549 × 10 A·cm, high pitting potential E at 0.165 V, the largest arc radius, and the largest sum of R and R at 5909 Ω·cm. For the sample annealed at 923 K, passivation did not occur, with low E at -0.075 V, large i at 1.879 × 10 A·cm, the smallest arc radius, and the smallest sum of R and R at 2173 Ω·cm, 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 ZrO, CuO, CuO, Ni(OH), AlO, and NbO.