Microstructure and electrochemical behavior of Ti-coatedZr55Al10Ni5Cu30 bulk metallic glass

In this study, pure Ti was coated on Zr55Al10Ni5Cu30 bulk metallic glass (BMG) using a physical vapour deposition (PVD) technique with magnetron sputtering. Microstructures of Ti coating, BMG substrate and interface were investigated by conventional and high-resolution transmission electron microscopy (TEM and HREM). The electrochemical behavior of Ti-coated Zr55Al10Ni5Cu30 BMG was studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in Hanks' solution. Scanning electron microscopy (SEM) was used to characterize the surface morphology of the coating after electrochemical testing. HRTEM observation reveals that the sputtering Ti coating consists of α-Ti nano-scale particles with the size about 10 nm. The polarization curves revealed that the open-circuit potential shifted to a more positive potential and the passive current density was lower after Ti coating was applied in comparison with that of the monolithic Zr55Al10Ni5Cu30 BMG. Electrochemical impedance spectroscopy (EIS) measurements showed that the Bode plots of Ti-coated Zr55Al10Ni5Cu30 BMG presented one time constant for 1 h and 12 h immersion and two time constants after 24 h immersion. The good bonding condition between Ti coating and Zr55Al10Ni5Cu30 BMG substrate may be responsible for the high corrosion resistance of Ti-coated Zr55Al10Ni5Cu30 BMG.