Microstructure And Electrochemical Properties Of Ti-35Nb-2Ta-3Zr/TiO₂ Composites Modified By FSP

Purposes: Micro/nano-sized TiO₂ particles were used as reinforcing phase to fabricate Ti-35Nb-2Ta-3Zr/TiO₂ micro/nano-composites with integrated structural TiO₂ micro/nano-composite surface layers by FSP,with the new titanium alloy Ti-35Nb-2Ta-3Zr of high strength and low elastic modulus as the matrix.Microstructures,composition changes and corrosion resistance of the composite layers were studied to provide prospect of industrialization and theoretical basis for clinical application of the micro/nano-composites.Methods: Ti-35Nb-2Ta-3Zr/TiO₂ micro/nano-composites were fabricated with the Ti-35Nb-2Ta-3Zr substrate by FSP.Microstructures and element composition of the composite layer on the micro/nano-composites were observed and analyzed by scanning electron microscopy,transmission electron microscopy,XRD and EBSD.Electrochemical corrosion parameters of the micro/nano-composite layer were analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy.The surface morphological changes of the micro/nano-composite layer were observed by atomic force microscopy after corrosion.X-ray photoelectron spectroscopy and depth profiles were used to explore composition and thickness of the surface oxide film.The reasons for differences in corrosion resistance of the micro/nano-composite layer were summarized,and the internal relations between corrosion resistance and microstructures were analyzed.Results: Ti-35Nb-2Ta-3Zr/TiO₂ micro/nano-composites with TiO₂micro/nano-composite layers were fabricated by FSP.TiO₂micro/nano-composite layers possess massive uniform refined grains of8?m with homogeneous dispersive oxygen on the surface.Nanocrystallines,amorphous phases and ?? martensites are discovered.The average misorientation angle is 22.34° and the fraction of high angle grain boundaries is 62.12% in the micro/nano-composite layers.Dynamic recrystallization occurred in the micro/nano-composite layers accompanied by many dislocations and deformation.The micro/nano-composite layers possess low corrosion current of 22.85 n A/cm2 and passive corrosion current of 2.1 ?A/cm2,high breaking voltage of 1.1V and a stable passive phase.The impedance of passive inner layer is 1346 k? cm2,and wide frequency range of peak angle and high phase angles of 81.07° are obtained,indicating outstanding corrosion resistance of the micro/nano-composite layers.With the increase of TiO₂ addition and rotation speed,corrosion resistance of the micro/nano-composite layers has promoted.The micro/nano-composite layer oxide film contains high-valent titanium oxides of 90.07%,and the surface is filled with nanosized needle-like structure.The surface of the micro/nano-composite layer is composed of a thick and dense inner protective layer of 60 nm and a thin porous outer layer structure.However,the surface of the substrate is composed of a thinner inner protective layer of 40 nm and a thicker flat outer layer.Conclusions: Ti-35Nb-2Ta-3Zr/TiO₂ micro/nano-composites of integrated structural TiO₂ micro/nano-composite layers were fabricated with the Ti-35Nb-2Ta-3Zr substrate by FSP.TiO₂ micro/nano-composite layers impart optimized microstructures and outstanding corrosion resistance to the surface of Ti-35Nb-2Ta-3Zr/TiO₂micro/nano-composites.More TiO₂ addition and higher rotation speed have a positive effect on corrosion resistance of TiO₂micro/nano-composite layers.