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

Abstract 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 TiO 2 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 × 10 –7 A/cm 2 to 7.92 × 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 × 10 4 Ω·cm 2 to 2.493 × 10 5 Ω·cm 2 .