Study on corrosion resistance of TC4 titanium alloy micro-arc oxidation/(PTFE plus graphite) composite coating

Micro-arc oxidation (MAO) coating was prepared on the surface of TC4 titanium alloy and sealed with (polytetrafluoroethylene [PTFE] + graphite) emulsion to obtain MAO/(PTFE + graphite) composite coating. The surface morphology and phase composition of the MAO coating were studied by scanning electron microscope (SEM) and X-ray diffractometer (XRD). The corrosion resistance of the coating was studied by the potentiodynamic polarization curve and the scanning Kelvin probe (SKP) micro-area voltage. The results show that the TiO2 ceramic oxide coating formed on the surface of the titanium alloy substrate has the characteristics of porous structure, which will become a channel for corrosive media to enter the coating and accelerate the corrosion of the MAO coating. However, the MAO/(PTFE + graphite) composite coating can prevent corrosive media from entering the coating and improve the corrosion resistance of the composite coating. The corrosion potential increased from 0.146 V to 0.241 V, the corrosion current density decreased from 4.31 x 10(-7) A/cm(2) to 7.92 x 10(-8) A/cm(2), and the self-corrosion current dropped to one fifth of the MAO coating. In addition, the charge transfer resistance has also increased from 5.305 x 10(4)omega center dot cm(2) to 2.493 x 10(5)omega center dot cm(2).