Nanocomposite bilayer film for resisting wear and corrosion damage of a Ti–6Al–4V alloy

A nanocomposite NiSi2/Ti5Si3 bilayer film was engineered onto Ti–6Al–4V alloy by double cathode glow discharge. The outer layer of the resulting film comprised of NiSi2, having dense and fine-grained (35 nm in size) columnar structure with a fraction of nanoscale twin bundles, and the inner layer consisted of equiaxed Ti5Si3with a grain size of 50 nm. Nanoindentation was carried out on polished cross-sections to measure the elastic modulus and hardness of each layer of the as-deposited film. Scratch tests were undertaken to evaluate the resistance of the as-deposited film to both abrasive and adhesive damage. The dry sliding wear experiments were conducted against ZrO2 ceramic balls under the applied load ranging from 3.3 N to 4.8 N at room temperature and 500 °C using a ball-on-disc tribometer. Compared with the Ti–6Al–4V alloy, the specific wear rates of the alloy coated with the bilayer film decreased by one order of magnitude at room temperature and were further reduced by one order of magnitude at 500 °C. The electrochemical behavior of the coated alloy was characterized by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 5 wt.% HCl solution. The results revealed that nanocomposite NiSi2/Ti5Si3 bilayer film exhibited a higher corrosion resistance than the Ti–6Al–4V alloy.