Caracterização mecânica e de tribocorrosão de superfícies nanoestruturadas obtidas em superfícies de ligas Ti-Nb por oxidação anódica

Abstract

Ti and Ti-6Al-4V alloy are widely used to replace hard tissues due to their higher biocompatibility, corrosion resistance and suitable mechanical properties. Although, these metals have a poor wear performance, higher coefficient of friction and elastic modulus that restrict to the applications in the biomedical area. Besides, wear debris can result in inflammatory reactions that cause pain and the loss of implants by osteolysis. In order to replace these materials, new beta alloys composed by non-toxic elements, as Nb, Ta, Mo, have been proposed, which are corrosion resistant and have mechanical properties suitable for biomaterials applications. Nanotubes grown on titanium and its alloys can improve biocompatibility, surface wettability and corrosion resistance when compared to untreated materials. However, the poor adhesion of nanotubes on substrate limit it use for biomedical area. The aims of this work were studied the tribocorrosion and mechanical properties of new Ti alloys and of nanostructured films grown on them. The Ti-10Nb and Ti-35Nb alloys are composed by alpha (hcp) and beta (bcc) phases. The results obtained by instrumented indentation technique showed that the addition of beta stabilizer elements in alloys decreases the elastic modulus values and increase the hardness values of both alloys, comparing to cp-Ti. Nanoscratch tests showed that Ti and Ti-10Nb alloy had a similar mechanical behavior, whereas high amount of β phase in the Ti-35Nb affected the plastic and elastic behavior. The results of tribocorrosion showed that, during the sliding, the Ti-Nb alloys were more resistance to corrosion than pure Ti. The coefficient of friction obtained were 0.56, 0.49, 0.90, to Ti, Ti-10Nb and Ti-35Nb, respectively. Ti and Ti-10Nb alloy showed a similar wear rate (~0.60. 10-3 mm³/N.m) and Ti-35Nb alloy disclosed the highest wear rate (~1.39. 10-3 mm³/N.m). The images of worn tracks revealed abrasive, adhesive and oxidative wear for all samples. However, the presence of beta phase was responsible for the strongest adhesion wear and the highest wear rate of the Ti-35Nb alloy. On Ti-10Nb alloy was grew a self-organized nanotube arrays on the alpha phase and walls with transversal holes on beta phase, forming an amorphous film with 1.5 μ m thick after annealed at 230 °C. Whereas a self-organized nanotubes were obtained on Ti-35Nb alloy with approximately 2.0 μm thick; their composition was a TiO2 and Nb2O5 crystalline phases mixture after annealed at 530 °C. The presence of phosphorus ions incorporated into the anodic layers makes the surfaces hydrophilic. The porous structure of nanostructured films contributed to very low hardness and elastic modulus. The film grown on Ti-10Nb alloy was removed of substrate during the nanoscratch and tribocorrosion tests due to it low crystallinity and poor adhesion. Whereas, a compact oxide grew between substrate and nanotubes, which promoted the adhesion of nanotubes on Ti-35Nb alloy. Therefore, it were compacted on the surface after mechanical tests, so; the outer part of the film was damaged. Its tribocorrosion performance was enhanced through a lubricating effect provided by oxide nanotube films grown on Ti-35Nb alloy, which showed the lowest wear rate [(0.052 ± 0.004)·10−3 mm/³Nm]. To summarize, the untreated Ti-10Nb and the anodized Ti-35Nb alloy were more suitable than titanium, regarding mechanical properties, for use in bone implants.