Fabrication and deformation behaviour of multilayer Al2O3/Ti/TiO2 nanotube arrays

In this study, titanium thin films were deposited on alumina substrates by radio frequency (RF) magnetron sputtering. The mechanical properties of the Ti coatings were evaluated in terms of adhesion strength at various RF powers, temperatures, and substrate bias voltages. The coating conditions of 400 W of RF power, 250 °C, and a 75 V substrate bias voltage produced the strongest coating adhesion, as obtained by the Taguchi optimisation method. TiO2 nanotube arrays were grown as a second layer on the Ti substrates using electrochemical anodisation at a constant potential of 20 V and anodisation times of 15 min, 45 min, and 75 min in a NH4F electrolyte solution (75 ethylene glycol: 25 water). The anodised titanium was annealed at 450 °C and 650 °C in a N2 gas furnace to obtain different phases of titania, anatase and rutile, respectively. The mechanical properties of the anodised layer were investigated by nanoindentation. The results indicate that Young’s modulus and hardness increased with annealing temperature to 650 °C.