Corrosion and tribocorrosion behavior of ZrO2-Al2O3 composite coatings developed by plasma electrolytic oxidation for load-bearing implants

The aim of this study was to develop a ZrO2-Al2O3 composite coating with excellent mechanical, corrosion, and tribocorrosion behaviour on Zr-2.5Nb alloy substrate for load-bearing implants. The bipolar waveforms utilizing cathodic duty cycles of 10, 20, and 40 were applied to produce composite coatings using the plasma electrolytic oxidation in an aluminate-phosphate electrolyte bath. The ZrO2-Al2O3 composite coatings had a net-like morphology with pores and cracks. When the cathodic duty cycle increased to 40, the Al2O3 was accumulated on the surface, with an enhanced thickness (5.39±0.67µm) and compactness of the coating with significantly improved hardness (2x higher). The composite coating developed at the cathodic duty cycle of 40 displayed the highest corrosion performance in phosphate buffer saline (PBS) even after 16 weeks of immersion. Moreover, the tribocorrosion test indicated the lowest volume loss of about 0.038 mm3 and showed no potential fall-out during the sliding test against the SiC ball. In summary, the ZrO2-Al2O3 composite coating developed by the PEO process resulted in noticeable corrosion and tribocorrosion performance of the Zr-2.5Nb alloy desirable for knee implants. [Display omitted] •ZrO2-Al2O3 composite coatings were synthesized using bipolar waveform with cathodic duty cycles of 10, 20, and 40.•The pores in outer layer of the coatings were sealing by ZrO2 and Al2O3 formation.•The D40 coating showed the best microhardness and corrosion performance in phosphate buffer saline (PBS).•The lowest volume loss was also achieved for the D40 coating in tribocorrosion test.