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.

This study focuses on surface modification of aluminum alloys (Al–Si) with high silicon content using plasma electrolytic oxidation (PEO). The influence of Al₂O₃ and SiO₂ particles, introduced both separately and in combination, into a sodium aluminate-based electrolyte during high-frequency treatment (2000 Hz). Examination of surface and cross-sections using a scanning electron microscope SEM showed an increase in the compactness of the coating when Al₂O₃ particles were introduced. The addition of SiO₂ particles tended to promote a smoother surface and a slight reduction in the porosity and defect density. However, when these particles are added together, especially at high concentrations, an increase in structural defects and crack formation is observed. X-ray diffraction analysis revealed that the γ-Al₂O₃ phase was present in all coatings. In the samples with Al₂O₃ addition, the α-Al₂O₃ diffraction signal became stronger compared with the other coatings. Tribological tests revealed that the addition of Al₂O₃ particles significantly improved wear resistance, while the introduction of SiO₂ particles contributed to the stabilization of the friction coefficient. Thus, Al₂O₃ particles were the most effective in enhancing the mechanical properties of the coating.

Tungsten borides are promising superhard materials, but their mechanochemical synthesis requires prolonged processing, leaving the early and intermediate stages of mechanical alloying (MA) and the role of boron content largely unexplored. This study investigated the effect of boron content and high-energy MA duration (2–10 h) on the morphology, particle size distribution, and structural and phase evolution of W–B powder mixtures, comparing a near-stoichiometric W90B10 composition with a boron-excess W80B20 composition. Scanning electron microscopy, laser diffraction, X-ray diffraction, and TEM-EDS were used for characterization. The average particle size of W90B10 initially increased to 3.48 μm after 6 h and then decreased to 1.28 μm after 10 h, whereas W80B20 exhibited non-monotonic behavior, stabilizing at approximately 4.3 μm. With increasing MA duration, bcc-tungsten reflections broadened and weakened, indicating a highly disordered nanocrystalline state. Reflections of hexagonal WB₂ (crystallite size 12.5 nm) appeared in W90B10 after 8 h, whereas no crystalline boride phases were detected in W80B20 up to 10 h. TEM–EDS and SAED analyses revealed local compositional inhomogeneity and provided additional crystallographic support for the formation of nanocrystalline WB₂. These results show that boron content determines the kinetics of boride phase formation and the morphology evolution pathway during MA, identifying W90B10 as the more favorable composition for rapid nanocrystalline WB₂ synthesis.