Formation of ZrO2 coating on the NiTi alloys for improving their surface properties

ZrO2 films were fabricated by plasma immersion ion implantation and deposition (PIIID) on the polished NiTi alloys. The results obtained from X-ray diffraction (XRD) and scanning electronic microscopy (SEM) showed the dense and well adhered ZrO2 coating were successfully fabricated by PIIID. Pin-on-disc and scratch tests revealed the surface friction coefficient of NiTi alloys was decreased due to the ZrO2 coating and good adhesion strength between the coating and substrate was obtained, respectively. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies indicated a significantly larger increase of the coated sample in the corrosion resistance compared with the uncoated samples. The mechanism of the improvement in the corrosion resistance of NiTi alloys due to ZrO2 coating was clarified.