Study on the Wear and Corrosion Resistance of PEO/SAM/MWCNTs Composite Coating on TC4/Mg Interpenetrating Composite

To address the severe wear and galvanic corrosion of TC4/Mg three-dimensional interpenetrating composites caused by the potential difference and hardness disparity between the two phases, this work proposes a hybrid surface modification strategy combining plasma electrolytic oxidation (PEO) with a self-assembled monolayer (SAM) doped with multi-walled carbon nanotubes (MWCNTs). A PEO ceramic coating was first grown in situ on the composite surface, followed by sealing modification using MWCNTs-containing SAM. The microstructure, phase composition, tribological behavior and potentiodynamic polarization curves of the coatings were systematically evaluated. The results show that the PEO coating is mainly composed of Mg₂SiO₄, MgO, MgF₂ and TiO₂, exhibiting a typical porous structure. After the MWCNTs-doped SAM composite modification, the nano-fillers and the molecular layer synergistically seal the micropores and cracks, and the surface transforms into a continuous and dense layered morphology. Wear tests reveal that the composite coating reduces the friction coefficient to 0.195 and decreases the wear volume by 93.53% compared with the bare composite. The "micro-roller bearing" effect and debris adsorption of MWCNTs significantly improve the wear resistance, and the dominant wear mechanism changes from abrasive wear to three-body wear. Electrochemical measurements show that the corrosion current density of the composite coating decreases from 2 × 10^-4 A·cm^-2 (bare composite) to 1.401 × 10^-9 A·cm^-2, i.e., a reduction by five orders of magnitude, with a protection efficiency of 99.99%. This is attributed to the physical barrier effect of the PEO coating and the synergistic sealing of defects, as well as the blocking of electron transfer by MWCNTs/SAM. The multi-level protection system of "PEO + MWCNTs + SAM" constructed in this work achieves a synergistic improvement in both wear resistance and corrosion resistance of the TC4/Mg two-phase interpenetrating composite, and holds promise for further investigation as an osseointegration implant material.