Microstructure and mechanical properties of anodized surface of ultrafine-grained Ti-13Nb-13Zr alloy for biomedical application

Abstract

Anodized surface on coarse-grained (CG) and ultrafine-grained (UFG) Ti-13Nb-13Zr alloy was obtained using electrochemical surface modification in the 1M H3PO4 + NaF electrolyte. Scanning electron microscopy (SEM) was used to characterise the microstructure of anodized surface, while mechanical surface properties were determined from the nanoindentation test. Numerical analysis of deformation of oxide film exposed to nanoindentation is performed on simplified 2D finite element models, with the main aim to determine the influence of the dimensions of the nanotubes on resistance to external loading. Software package Simulia Abaqus is used. It was shown that the homogeneous oxide film was formed at longer time period, while inhomogeneous oxide film was formed at shorter time period, for both materials. The oxide film was composed of nanotubes, whose deformation after the nanoindentation test is characterized by SEM. The surface of anodized alloys has lower mechanical surface properties (modulus of elasticity and nanohardness) than surface of non-anodized ones, which make them more acceptable for biomedical usage. Numerical calculations revealed the influence of morphology of the anodized surface layer on its load carrying capacity