Structure and properties of Al2O3 coatings formed on NiTi alloy by cathodic plasma electrolytic deposition

Al2O3 coatings were prepared on NiTi alloy by cathodic plasma electrolytic deposition (CPED) in an aluminum nitrate solution. Scanning electron microscopy (SEM) shows that the coating exhibits a typical porous surface, rough micro structure and excellent adhesive interface between the coating and the substrate. Energy dispersive X-ray spectrometer (EDS) shows that when the treatment time is 45min, this ceramic coating is composed of Al, O, and C with the atomic concentration of 43.37%, 48.52% and 8.11%, respectively, and the concentration of Ni is lower than the minimum instrument detection standard. X-ray diffraction (XRD) indicates that the coating consists of α-Al2O3 and γ-Al2O3 crystal phase. Direct pull-off test shows that the coating on NiTi substrate has a mean coating-substrate bonding strength of 15±2MPa. Cross-sectional hardness measurement illustrates that the average microhardness of the coating is less than the values of this parameter for the substrate. The results of potentiodynamic polarization test indicate that the corrosion resistance of the coated sample is increased by 3 times compared with that of the uncoated sample on the basis of corrosion current density. Al2O3 coatings were prepared on NiTi alloy by cathodic plasma electrolytic deposition (CPED) in an aluminum nitrate solution. The amount of Ni on the surface layer is reduced to a larger extent and the corrosion resistance of the coated sample is increased by 3 times compared with that of the uncoated sample on the basis of corrosion current density. [Display omitted] •Al2O3 ceramic coating was successfully prepared on NiTi alloy by cathodic plasma electrolytic deposition. The thickness of the coating is about 90μm and the α-Al2O3 is the dominant composition in the cathode plasma electrolytic deposition coatings.•The amount of Ni is reduced to a larger extent.•The corrosion resistance of the coated sample is increased.