Micro-scaled morphology of Ti-40Nb-xZr alloy with applied voltage via plasma electrolytic oxidation

Abstract

In this study, the formation of micro-scale morphology on Ti-40Nb-xZr alloys was investigated under plasma electrolytic oxidation (PEO) treatment. By varying the Zr content to 0, 3, 7, and 15 wt.%, non-toxic, low-modulus alloys were prepared. PEO was then performed using a direct current power source with the sample as the anode and a carbon rod as the cathode in an electrolyte solution of 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophosphate. The applied voltage was varied from 180–380 V at a current density of 75 mA for 3 min. In the Ti-40Nb-xZr alloys, as the Zr content increased, the microstructure changed from a needle-like structure to an equiaxed structure, and the elastic modulus and hardness in nanoindentation tests decreased (from 120 to 67 GPa and 4.55 to 2.00 GPa, respectively). As the applied voltage increased during the PEO process, the pore size increased. The TiO2 layer formed on the alloy surface contained Ca and P from the electrolyte. The surface roughness obtained from atomic force measurements was the lowest in the bulk samples (0.133 to 0.024 μm), and it gradually increased as the applied voltage increased and decreased as the Zr content increased. As the applied voltage increased, the contact angle decreased, whereas as the Zr content increased, the contact angle increased.