In-situ incorporation of Ce-zeolite during soft sparking plasma electrolytic oxidation

This study demonstrates that the optimisation of electrical processing parameters during plasma electrolytic oxidation allows the single-step incorporation of nanoparticles with complex 3D structures into the outer porous structure of the growing PEO coating. In particular, this work evaluates the zeolite particle uptake mechanism during the soft sparking regime. Four aluminate-based electrolytes with different concentrations of zeolite nanoparticles (0–10 g l⁻¹) were studied. The encapsulation of Ce within the zeolite nanoparticles (Ce-zeolite) was evaluated by FTIR, SEM/EDS, XRD and TGA. The successful incorporation of zeolite in PEO coatings was confirmed by SEM-EDS and FIB/TEM. Zeolite and Ce-loaded nanoparticles were incorporated non-reactively by adsorption and entrapment into molten oxide during coating growth at the surface of PEO coatings. Reactive incorporation was also identified in the inner layers as a result of the field assisted migration of the nanoparticles through flaws and defects, leading to their thermal decomposition. The corrosion behaviour of PEO coatings improved noticeably upon the addition of zeolite nanoparticles, whereas the inclusion of cerium within zeolite led to an incremental improvement in performance.