Development of new β/α″-Ti-Nb-Zr biocompatible coating with low Young's modulus and high toughness for medical applications

Ideal biomaterials to fabricate orthopedic implants, especially for load-bearing joint replacements, should include only non-toxic elements with good biocompatibility, high corrosion resistance and surface bioactivity, together with a good combination of mechanical properties. Based on these criteria, a manufacturing approach based on sputtering techniques can be ideal to develop coatings free of toxic elements tailored for advanced applications on pure titanium or titanium alloys used in biomedical applications. In this work, the ternary Ti-Nb-Zr system was used to develop non-toxic β-rich Ti coatings with several complex microstructures by careful control of Nb and Zr concentration and deposition parameters, such as bias voltage. Depending on the alloy chemistry and processing, the coating included variable amounts of α-, α″- and β-phases of Ti with different morphologies and crystallographic texture. Mechanical properties of every coating is largely determined by the micro-structure present, which is directly related to bias voltage used during sputtering process. Thus, hardness values change as a function of the compressive residual stresses magnitude and Young's modulus decreased from 63 GPa, at 0 V, to 47 GPa, at −63 V, being this value close to human bone (~30 GPa). After that, Young's modulus progressively increases to 89 GPa, at −148 V. On the other hand, bioactivity of the coating is practically doubled when compared to Ti6Al4V alloy.The authors wish to express their thanks for the financial support of the Czech Science Foundation through the projects GACR 14-32801P and GACR 31-16-140245. Nano-characterization was carried out on equipment funded by EPSRC through EP/K005103/1 project. We are also grateful to CENIM’'s X ray laboratory for the support given on the analysis of XRD patterns. M.K. would like to acknowledge financial support of the ERDF in the frame of the project No. CZ.02.1.01/0.0/0.0/15_003/0000485.Peer Reviewe