Structural and mechanical behavior of titanium based oxide thin layer for biomedical application

Abstract

The Ti-13Nb-13Zr alloy made by conventional methods (coarse-grained, CG) was examined, as well as the alloy and commercially pure titanium (cpTi) after the high pressure torsion (HPT) process (ultrafine-grained, UFG) performed at room temperature. All materials were subjected to nanostructured surface modification. Nanostructured surface modification was done in 1M H3PO4 + 0.5 wt. % NaF electrolyte during 60 and 90 minutes, for the desired potential of 25V with a scan rate of 100 mVs-1. As the result of the nanostructured surface modification nanotubular titanium based oxide layer was obtained. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterize the homogeneity of nanotubular titanium based oxide layer and dimensions of the formed nanotubes. In order to define the chemical structure of oxide layer, energy dispersive spectroscopy (EDS) was used. The obtained results indicate that the duration of the nanostructured surface modification significantly affects on the homogeneity of the nanotubular titanium based oxide layer morphology, as well as on the dimensions of the nanotubes (diameter and wall thickness of the nanotubes). Also, the effect of the HPT process on the homogeneity and thickness of the nanotubular oxide layer (length of the nanotubes) are shown and discussed. The mechanical behavior of nanotubular titanium based oxide layer was examined by nanoindentation test. The control of nanoindentation test was done by total displacement. The displacements were 2000 nm for non-modified surface and 10% of the thickness of nanotubular titanium based oxide layer for modified surface. The test was performed on a nanoindenter using as an indenter the Berkovich-type diamond tip. As results, loading-displacement curves and the mean value of ten measurements of the surface modulus of elasticity and nanohardness were obtained. Also, in order to characterize deformation of the oxide layer after nanoindentation SEM was done. Having in mind that nanotubular oxide thin layer can affect tensile properties of metallic materials, tensile testing was performed.