Effect of anodizing time on the hardness and tribological properties of Ti–6Al–4V

Electrochemical anodization of the Ti–6Al–4V alloy was performed using two types of organic electrolytes, one of NH 4 F in ethylene glycol and the other of NH 4 F in glycerol. The anodization times and voltages were varied to observe changes in the hardness and friction coefficients. Hardness values of 4.14 GPa and 4.68 GPa were achieved for ethylene glycol and glycerol, respectively. Relative to the untreated alloy the friction coefficient decreased to a value of 0.45 for both electrolytes. These improvements are attributed to the formation of TiO 2 nanotubes with diameters ranging from 27 to 86 nm. Graphical abstract