Surface elastic properties of Ti alloys modified for medical implants: a force spectroscopy study.

We report here the first nanoscale surface elasticity measurements on surface-modified titanium alloys using the force spectroscopy mode in scanning force microscopy. Samples of three vanadium-free titanium alloys, Ti-7Nb-6Al, Ti-13Nb-13Zr and Ti-15Zr-4Nb, were investigated. Surface modification of the three alloys was produced by thermal oxidation in air at 750 degrees C for different times, which resulted in the formation of protective oxide layers with different surface composition and morphology. The elastic properties of the surface layers were studied comparatively in the as-received Ti alloys and after the oxidation process using cantilevers with different stiffness to evaluate the influence of the indentation depth. In all cases, Young's modulus of the sample surfaces was found to be lower than 65GPa, and as low as 20GPa for some of the oxidized samples. Variations observed for the three oxidized Ti alloys can be related to the different chemical composition of the outer layers generated for the different oxidation times.