The Role of Signal Waveforms in Plasma Electrolytic Oxidation

Plasma electrolytic oxidation (PEO) is often used to improve the physical and mechanical properties of valve metals. This method allows for the formation of thicker and denser metal oxide coatings, which helps to improve physical and mechanical properties, especially the wear and corrosion resistance of the surface. The PEO process is widely used in areas such as mechanical engineering, aerospace, biomedical, and others. This review aims to summarize and explain the fundamental principles of the PEO process, with a focus on the influence of waveform types and their parameters on the properties of PEO coatings. This study found that a sinusoidal waveform promotes the generation of more stable discharges compared to a rectangular waveform, thereby enhancing the corrosion resistance of the coatings. Furthermore, it was demonstrated that using a rectangular waveform with adjustable parameters enables the production of thicker and more wear-resistant coatings. Meanwhile, the application of sawtooth and trapezoidal waveforms reduces sharp current spikes during the onset of discharges, minimizing defect formation and positively influencing the coating formation process. In addition, bipolar and unipolar modes are analyzed, and the promising future directions are discussed.