Statistical optimization and fretting fatigue study of Zr/ZrO₂ nanotubular array coating on Ti-6Al-4V

Herein, the fretting fatigue behavior of zirconium nanotube arrays on the surface of Ti-6Al-4V is studied. Initially, a thin film of pure zirconium (Zr) was deposited onto a Ti-6Al-4V substrate using physical vapor deposition (PVD) magnetron sputtering for the primary layer at varying DC power, temperature and substrate bias voltage values. To obtain higher adhesion strength, the Taguchi optimization method was used to estimate the optimum coating parameters, while a Pareto ANOVA was employed to determine the significant parameters. The strongest coating adhesion, as determined by a scratch force test, was achieved at 300W DC power, 200°C and a 75V bias voltage. Consequently, nanotubes were produced via Zr anodization in an NH₄F electrolyte solution (95 glycerol:5 water) at different times and at a constant potential of 60V (second layer). The fretting fatigue behavior of anodized samples annealed at 400°C and 800°C was investigated. The results indicate that the fretting fatigue life of the ZrO₂ nanotube-coated samples was significantly improved at low and high cyclic fatigue at an annealing temperature of 400°C compared to the uncoated samples.