Electrophoretic deposition and microstructure development of Si3N4/polyetheretherketone coatings on titanium alloy

Abstract

Nanocomposite Si3N4/PEEK coatings were deposited on the model Ti-13Nb-13Zr titanium alloy by cathodic electrophoretic deposition. The use of different dispersion media and surfactants, the cationic polyelectrolytes polyethylenimine and chitosan, added to the suspensions has been studied. Understanding of the deposition mechanism process was obtained by monitoring the suspension properties, concentration of coating components, pH and zeta potential as well as investigation of interaction between solid particles in the suspension by electron microscopy. Based on the electrokinetic properties of suspensions and observations of the as-deposited coating morphology, the electrophoretic co-deposition of amorphous Si3N4 nanoparticles and PEEK micro-particles parameters, constant voltage and deposition time, were elaborated. It was found that the coating, 120 μm thick, deposited from the suspension containing a low amount of Si3N4 stabilized by chitosan under a constant voltage of 15 V during 90 s and with a constant distance between electrodes of 10 mm, was homogeneous. The coating structure and morphology changed as a result of post-deposition heat treatment from amorphous with a granular morphology into a semi-crystalline continuous and solid matrix. The separate Si3N4 nanoparticles and their agglomerates were relatively homogeneously distributed within the PEEK matrix. The coatings deposited from the suspension containing chitosan exhibited higher scratch resistance than the coatings deposited from the suspension stabilizing by polyethylenimine. The results demonstrate that electrophoretic deposition is a useful method to deposit homogeneous composite Si3N4/PEEK coatings well-adhered to the titanium alloy substrate, which could potentially improve both the bioactive and bio-tribological properties of titanium alloys used in biomedical applications.