Abstract
Titanium alloys are well recognized as appropriate materials for biomedical implants. These devices are designed to operate in quite aggressive human body media, so it is important to study the corrosion and electrochemical behavior of the novel materials alongside the underlying chemical and structural features. In the present study, the prospective Ti‒Zr-based superelastic alloys (Ti-18Zr-14Nb, Ti-18Zr-15Nb, Ti-18Zr-13Nb-1Ta, atom %) were analyzed in terms of their phase composition, functional mechanical properties, the composition and structure of surface oxide films, and the corresponding corrosion and electrochemical behavior in Hanks’ simulated biological solution. The electrochemical parameters of the Ti-18Zr-14Nb material in bulk and foam states were also compared. The results show a significant difference in the functional performance of the studied materials, with different composition and structure states. In particular, the positive effect of the thermomechanical treatment regime, leading to the formation of a favorable microstructure on the corrosion resistance, has been revealed. In general, the Ti-18Zr-15Nb alloy exhibits the optimum combination of functional characteristics in Hanks’ solution, while the Ti-18Zr-13Nb-1Ta alloy shows the highest resistance to the corrosion environment. The Ti-18Zr-14Nb-based foam material exhibits slightly lower passivation kinetics as compared to its bulk equivalent.
Highlights
Materials 2019, 12, 2395 mismatch between the implant and the surrounding bone tissue, leading to stress shielding, are still problems to be solved [3,5,6,7,8]. The latter difference is underlined by the fact that natural bone possesses a low Young’s modulus and hysteresic mechanical behavior upon loading-unloading cycles. From this point of view, biomechanically compatible titanium implant materials can be designed in two different ways [9,10,11]
The superelasticity effect can be exhibited by a material due to reversible martensitic transformation upon loading and unloading, resulting in reversible strain values of several percentage points [20]
Near-equiatomic Ti-Ni alloys represent the most widely used shape memory and superelastic materials for various technical and biomedical applications [23]. Their use as an intraosseous implant material is limited by the nickel toxicity
Summary
Materials 2019, 12, 2395 mismatch between the implant and the surrounding bone tissue, leading to stress shielding, are still problems to be solved [3,5,6,7,8] The latter difference is underlined by the fact that natural bone possesses a low Young’s modulus and hysteresic mechanical behavior upon loading-unloading cycles. It is established that the presence of this phase transition is accompanied by lattice softening, leading to a significant decrease in the Young’s modulus [21,22] In this context, near-equiatomic Ti-Ni alloys represent the most widely used shape memory and superelastic materials for various technical and biomedical applications [23]. Ni-free superelastic titanium alloys have been designed and characterized extensively over the past two decades [24,25,26]
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