Structure and nanoindentation mechanical properties of novel porous Ti-Ta material with a core-shell structure using the powder metallurgy method

Abstract

In this paper, results from microstructural and nanoindentation studies of novel Ti-Ta core–shell structured type materials for potential biomedical applications are presented. The use of Ta as the outer coating of the Ti core allows the creation of a light and porous material with potentially increased resistance to corrosion. Ti–Ta core–shell particles were fabricated using the powder metallurgy method by the ball milling of elemental powders and subsequently sintered at 1000 °C for 24 h. The specimens were examined using scanning and transmission electron microscopy, X-ray diffraction, atomic force microscopy and nanoindentation methods. The compositions of the prepared materials were detected using energy dispersive spectroscopy and X-ray fluorescence methods. The FIB technique in combination with high resolution TEM ensured proper sample preparation and description of the structure of the material. The results indicate that the core–shell particles have inhomogeneous microstructures and compositions. A core-shell structure, consisting of Ti-rich cores and Ta-rich shells formed due to diffusion between the Ti and Ta powders. The outer part of the particles contains an area enriched in tantalum. Moving closer to the core, there is an equilibrium region of Ti and Ta, whereas the core is composed of pure titanium. A sintered two-phased (α + β) Widmanstätten-type microstructure was also observed. The mechanical studies indicated the presence of three main zones, different in terms of the mechanical properties inside of a particle. A formation model for the α, α + β and β phases during material synthesis was proposed.