Scratch-resistant and well-adhered nanotube arrays produced via anodizing process on β-titanium alloy

Abstract

Well-adhered nanotube arrays were produced through the anodizing technique on a Ti-25Nb-25Ta alloy and tribo-mechanically evaluated by nanoindentation and nanoscratch tests. Disregarding substrate effects, the hardness of the nanotube arrays layer was 0.7 ± 0.1 GPa and elastic modulus was < 12 GPa, respectively. With the load increase and nanotubes compaction, hardness reached 1.8 GPa and elastic modulus stabilized in ∼40 GPa, which features a mechanically biocompatible gradient zone for implant applications. Under scratching, plastic deformations predominated in the nanotube arrays coating, which mechanism was load-dependent: in the first stage (up to 50 mN) and the initial tubes collapsing, the coating presented low cohesive strength; under higher loads and the progressive nanotubes compaction, the cohesive strength increased, as suggested by the pattern of cracks produced. The scratch resistance for the coating failure was higher than 500 mN, consisting of an excellent bonding adhesion for a nanotube layer produced by anodization.