The effects of nano- and micro-particles on properties of plasma electrolytic oxidation (PEO) coatings applied on titanium substrates: A review

Plasma electrolytic oxidation (PEO) technique has been rapidly developed as a method of producing biocompatible, hard, corrosion-resistant, and wear-resistant as well as having good adhesion coatings in recent years. Due to the PEO coatings remarkable properties, they are used in order to modify the surface and improve properties of light metals such as aluminum, magnesium, titanium, etc. Since several parameters impact the microstructure and phase composition and subsequently the properties of PEO coatings, it is important to investigate the effects of these parameters and optimize them. One of these parameters that plays a major role in changing the properties of PEO coatings is the chemical composition of the electrolyte which can be altered by changing the components and/or their concentrations and adding different nano- and micro-particles. Due to the good performance of nano- and micro-particles in improving the corrosion behavior of PEO coatings, this review focuses on effects of particles addition into the electrolytes on corrosion behavior of PEO coatings on titanium in addition to its alloys. Also, in this review, the mechanism of embedding particles to PEO coatings and the effects of particles addition on phase composition, microstructure, roughness, adhesion, and thickness of coatings are discussed.