Electrochemical behavior and microstructural characterization of lanthanum-doped titanium-zirconium-molybdenum alloy

Lanthanum-doped titanium-zirconium-molybdenum (La-TZM) alloy with high strength and high toughness was prepared by powder metallurgy and rolling process. The influence of OH− concentrations (5%, 7% and 10%) on the electrochemical behaviors of La-TZM alloys was investigated by potentiodynamic polarization tests. Scanning electron microscopy (SEM) was used to characterize the microstructure and energy dispersive spectroscopy (EDS) was used to analysis the secondary phase. The electrochemical corrosion mechanism was analyzed comprehensively. The results reveal that the corrosion rate of La-TZM alloy first decreases and then increases with the increasing of OH− concentration. The pitting corrosion firstly occurs around the secondary phase particles (La-Ti-Zr-O), and expands along the grain boundaries and defects as the potential increasing. The addition of rare earth element La affects the formation of passive film on the surface and reduces the corrosion resistance of the alloy. The micro galvanic couples between the secondary phase and the matrix accelerate the corrosion of the base material. Therefore, according to the environment, the corrosion resistance and the mechanical properties should be both considered in the process of strengthening alloy with additive elements.