Influence of current density on the microstructure and corrosion resistance of PEO coatings on pure Zr

• Plasma electrolytic oxidation (PEO) coatings were applied on pure zirconium at varying current densities. • Monoclinic zirconia (m-ZrO₂) was the dominant phase in the coatings, with intensity increasing at higher currents. • Coatings at 300 mA/cm² showed minimal surface pores and fractures, ensuring better uniformity. • Electrochemical tests revealed the highest corrosion resistance for the coating at 300 mA/cm². This investigation involved the application of plasma electrolytic oxidation (PEO) coatings on pure Zr at current densities of 100, 200, 300, and 400 mA/cm², utilizing an electrolyte with a consistent duty cycle and frequency. All coatings displayed the monoclinic zirconium oxide (m-ZrO 2 ) phase in their phase structure. At a current density of 100 mA/cm², the intensity of peaks associated with the substrate phase was greater, with only partial peaks of m-ZrO 2 detected at the (-111) plane. Conversely, with elevated current densities, the intensity of substrate peaks diminished, and the monoclinic phase primarily emerged in the (-111) and (200) planes. Microstructural research indicated that at a current density of 100 mA/cm², no sparking transpired, and just the standard anodizing process occurred. At current densities of 200 mA/cm² and higher, a complete PEO oxide layer was detected. Augmenting the applied current density led to the formation of thicker coatings. The rise in current density resulted in a decrease in the quantity of surface pores, with the minimum pore count recorded in the samples at 300 and 400 mA/cm². The sample with a current density of 300 mA/cm² exhibited the least surface fractures. Also, The highest values of hardness and impact strength are obtained for the 300 coating. Electrochemical analyses revealed that the corrosion resistance of the 300 and 400 mA/cm² coatings surpassed that of the other coatings, with the 300 mA/cm² coating exhibiting the most superior corrosion performance. The current densities for samples at 100, 200, and 400 mA/cm² were 2.75 × 10⁻⁶, 3.16 × 10⁻⁷, and 3.09 × 10⁻⁸, respectively, however for the sample at 300 mA/cm², it diminished to 2.63 × 10⁻⁸.