Effect of applied voltage on surface properties of electrophoretic hybrid ZnO/HAp/PMEA coated stainless steel 316L

Abstract

During electrophoretic deposition (EPD), the deposition rate is crucial for preventing particle aggregation, which can lead to uneven distribution of nanoparticles on the SS316L surface. In this study, the deposition rate was optimized by analyzing the physical and surface properties of ZHP (ZnO (Zinc Oxide)/HAp (Hydroxyapatite)/PMEA (Polymethoxyethylacrylate)) nanocomposite coatings. The primary factors controlling the deposition rate with varied applied voltages (50 and 60 V) are temperature and current. At 60 V, the increased temperature reduces viscosity and improves the mobility of ZHP nanocomposites. Additionally, the increased current ensures a denser coating with fewer defects. To verify these effects, the physical properties of the ZHP nanocomposite coatings were characterized by surface analysis, X-ray diffraction, vibrational spectroscopy, and surface energy analysis. Among the ZHP nanocomposite coatings, ZHP-2 (0.115 % (w/V)–ZnO, 0.115 % (w/V)-HAp, 15.39 % (v/V)-PMEA, at 60V) showed a crack-free, less porous, and evenly distributed surface. X-ray diffraction analysis revealed that ZHP-2 had a reduced crystal diameter, increased micro-strain, decreased lattice constant, and increased dislocation density compared to ZHP-1 (0.115 % (w/V)–ZnO, 0.115 % (w/V)-HAp, 15.39 % (v/V)-PMEA, at 50V). Vibrational spectroscopy results confirmed the higher functionalization of the functional groups of additives and nanoparticles (ZnO and HAp) in ZHP-2. Lower surface energy indicated that hydrophobicity was present on the ZHP-2 coating. Further, the ZHP-2 showed significant improvements in surface properties such as general shear failure, higher hardness, lower roughness, higher bonding strength, higher scratch hardness, and shallower scratch depth. Therefore, the ZHP-2 nanocomposite coating exhibited a controlled deposition rate by reducing particle aggregation during EPD.