Microhardness and corrosion behavior of surface gradient oxide coating on the titanium alloy strips under high energy electro-pulsing treatment

The effects of high-energy electropulsing treatment (EPT) on the microhardness and corrosion behavior of the surface gradient oxide coating on the titanium alloy matrix were investigated using infrared thermoscope, micro-hardness, three-dimensional optical microscope, electrochemical work station, scanning electron microscope equipped with electron backscatter diffraction, X-ray Diffraction, Fourier Transform Infrared Spectroscopy and Thermogravimetry analyzer. Results showed that the surface modification brings in surface strengthening effect and improved surface corrosion resistance performance (in the fluoridated acidified artificial saliva) of titanium alloy strips with outstanding bonding-strength oxide coating through EPT transition zone. Rapid recrystallization, grain growth and texture evolution of surface matrix alloy are present with increasing DAFA (distance from the anode) of EPT. In this process, microstructure/texture evolution influences the oxidation layer thickness and the oxidation rate with the relationship between these two parameters fitting the approximate positive linear equation and the turning trend located at 120 mm DAFA. Compared with TG-traditional furnace heating process, the growth rate of oxidation under EPT is noticeably enhanced by two orders of magnitudes and surface oxide coating experiences a crystal transformation from anatase-TiO2 to rutile-TiO2. Ionization and acceleration of oxygen by EPT are put forward to discuss the accelerated growth and crystal transformation kinetics of the oxidation process. Therefore, improved surface wear resistance and anti-corrosion performance with a strong adherent gradient oxide coating on the titanium alloy strips surface can be achieved by highly-efficient EPT process which can be applied in biomedical applications.