Corrosion Resistance of ALD-Deposited HfO2 Coatings on Stainless Steel for Biomedical Applications

This study investigated the electrochemical protection provided by amorphous hafnium thin films deposited on austenitic stainless steel by atomic layer deposition technology that guarantees control over the physicochemical properties of deposited coatings and processes repeatability. Furthermore, ALD enables conformal coating of three-dimensional shapes. The corrosion resistance of these coatings was evaluated under conditions simulating physiological environments, using potentiodynamic polarization and electrochemical impedance spectroscopy. Furthermore, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy were employed to analyze the chemical stability, surface condition, and morphology of the films prior to and following electrochemical testing. Potentiodynamic polarization tests demonstrated that uncoated SS316L provided insufficient corrosion resistivity, whereas samples coated with ALD-grown hafnium dioxide thin films possessed barrier properties, exhibited a pronounced passive region and a reduction in anodic and cathodic current densities by up to three orders of magnitude. Electrochemical impedance spectroscopy results further verified the development of a compact, highly resistive dielectric interface. X-ray photoelectron spectroscopy analysis demonstrated that the films exhibited chemical stability following corrosion. SEM images showed that after electrochemical tests on stainless steel, significant surface degradation was observed, whereas the hafnium dioxide-coated surfaces remained unchanged. The findings suggested that films with a thickness of ≈100 nm act as effective barriers to corrosive ions. These results highlight the potential of ALD-deposited amorphous hafnium dioxide thin films as protective coatings against corrosion and present promising prospects for future biomedical applications.