ENGINEERING TITANIUM-BASED MATERIALS: HIGH-PRESSURE TORSION AND SURFACE NANOSTRUCTURING

Abstract

The coarse-grained (CG) and ultrafine-grained (UFG) Ti-13Nb-13Zr alloys were used as tested materials in this study. The UFG alloy was obtained using a high-pressure torsion process (HPT) under a pressure of 4.1 GPa with a rotational speed of 0.2 rpm up to 5 rotations at room temperature. The structure of titanium alloy may be modified by high-pressure torsion (HPT) which is one of the most popular severe plastic deformation (SPD) methods. HPT process leads to the forming of submicron-sized grains in structure. Also, the HPT process leads to improving the mechanical and corrosion properties of titanium alloy. In order to analyze the influence of the HPT process on the morphology and characteristics of the nanostructured surface, Ti-13Nb-13Zr alloy was modified by anodic oxidation.

Anodic oxidation in the 1M H₃PO₄ + NaF electrolyte was used as a method for the nanostructured surface of titanium-based materials. Scanning electron microscopy (SEM) was used to characterize the morphology of the surface, while surface roughness was determined using atomic force microscopy (AFM). The surface mechanical properties before and after the anodic oxidation were examined using the nanoindentation test. Corrosion resistance was tested in artificial saliva with a pH value of 5.5 at 37°C, to simulate the environment in the human body.

The impact of the HPT process on the morphology of the nanostructured surface (homogeneity of the modified surface, diameter, wall thickness, and length of nanotubes) has been shown. It has been shown that anodic oxidation increases the roughness of the surface, while this increase is more pronounced after the HPT process. Characterization of the CG and UFG TNZ alloy surface after anodic oxidation showed a decrease in the values of surface mechanical properties, whereby they approached the values of the mechanical properties of human bone tissue. Also, results showed that corrosion resistance was increased after anodic oxidation, for both materials.