Investigation and characterization of the plasma electrolytic oxidation of zirconium alloy: effect of negative duty cycle

In this investigation, the effect of negative duty cycle on the morphology and abrasion and corrosion resistance properties of plasma electrolytic oxidation (PEO)-induced coating on Zr–1%Nb alloy was investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM) with electron diffraction pattern (EDP) method and scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) corrosion and pin-on-disc tests were used to examine the structure and morphology of the coatings. A dense and homogenous structure of PEO coating under negative duty cycle conditions was fabricated that included compounds of crystalline and amorphous nanostructures with fewer nanopores. The results showed that the m-ZrO2 and t-ZrO2 were dominant phrases. Also, the corrosion resistance properties of all PEO layers with various conditions were significantly improved. The PEO layer formed with 20% negative duty cycle and the frequency of 1 kHz showed superior corrosion resistance, which could be attributed to its pore-free morphology. The abrasion resistance of the PEO layer at a higher frequency of 4 kHz was about 0.63 which was indicated improvement of abrasion behavior. In addition, the weight loss rate for the PEO layer with the 20% negative duty cycle was about 0.0002 g. The results demonstrated that the using of 1 kHz frequency and 20% negative duty cycle led to the formation of the PEO layer on the surface of Zr–1%Nb alloy with supreme corrosion and abrasion resistance properties.