Advances in plasma electrolytic oxidation (PEO) on metal-matrix composites (MMCs) - A critical review

Metal-matrix composites (MMCs) of aluminium, magnesium and titanium are significant for their prospective applications in the automotive, aerospace, and biomedical industries. While the reinforcements enhance the mechanical properties, they often negatively affect corrosion and wear resistance. One of the finest strategies to overcome this is plasma electrolytic oxidation (PEO), the electrochemical anodic oxidation process assisted by high voltage plasma conditions that leads to a firmly bound conversion oxide layer. The research and development on PEO-coated MMCs are comprehensively reviewed here. The variation of PEO layer morphology, composition, pore density, PEO discharge processes, growth kinetics, and the layer's surface hardness and adhesion are discussed with respect to the reinforcement type in the MMCs. The anti-corrosion and anti-wear characteristics of the developed PEO layers are detailed. Other applications are briefed. The collective information could help to foster better PEO/MMCs for commercial applications.