Rational design of compact ceramic coating on SiCp/Al composites by tailoring soft sparking discharge of plasma electrolytic oxidation

The characteristics of PEO processes on SiCp/Al composite in aluminate electrolyte under the influence of negative pulse were comparatively investigated, aiming to tailor the soft sparking discharge states, thus achieving the compact ceramic coating and providing a deep understanding of the mechanisms involved. Tracking the variation trend of element optical emission intensity by OES technology reflects the influence of negative voltage on the evolution of the spark state, and the results show that large negative voltage accelerates the transition from arc sparking discharge to soft sparking discharge. When the PEO process completely enters the soft spark discharge state, the lowest electron density can also be kept at 1.06 × 1022 m−3, reaching the local thermodynamic equilibrium condition. At this time, the electron temperature in the plasma discharge zone is about 4000 K. In addition, the coating surface roughness value decreases with the increase of negative voltage, and the introduction of negative voltage effectively reduces the irregular convex structures and the macropores in the coating, due to inhibiting destructive high-intensity spark discharge by the soft sparking discharge.