TiO2 Coatings Formed by Atomic Layer Deposition for Enhanced Corrosion Performance of Mg-biomaterials

Magnesium (Mg) alloys have experienced increased attention in the area of biomaterials due to Mg being considered a resorbable biomaterial. Mg alloy implants can potentially be designed to degrade in the body, thus an implant would not remain in the body for longer than is needed to perform its task. Mg and many of its alloys are considered to be biocompatible and non-toxic in the body; however, due to the high rate at which Mg degrades a negative host response is expected. A novel approach to inhibit corrosion rate using thin film coatings on a Mg alloy (AZ31B) via atomic layer deposition (ALD) is proposed. ALD is based on saturated surface reactions on the substrate unlike other thin film deposition techniques such as chemical vapor deposition (CVD) and physical vapor deposition (PVD). Sequentially-performed surface reactions between the substrate and precursor molecules water and titanium tetrachloride (H2O , TiCl4) result in thin film growth of amorphous titanium dioxide (TiO2). TiO2 is grown in an atomic layer-by-layer fashion during ALD allowing sub-nanometer thickness control of growth, with excellent coating uniformity and step coverage. TiO2 coatings and their impact on the corrosion resistance of AZ31B were characterized using atomic force microscopy, scanning electron microscopy, electrochemical impedance spectroscopy, and linear polarization measurements

Atomic Layer Deposition of Thin Film Oxides on Magnesium Alloys to Inhibit Corrosion.

Magnesium alloys are integrated into many performance consumer products because of their high strength to weight ratio; however, one of the major engineering hurdles of magnesium alloys is their susceptibility to corrosion in harsh environments, which limits their use in several applications. To overcome this limitation, we hypothesize that coating magnesium alloys with thin films of different chemistries via atomic layer deposition (ALD) will inhibit the effects of corrosion. While chemical and physical vapor deposition techniques have been used to coat Mg alloys, little work has been done using ALD. ALD is a thin film growth technique that uses cyclic self-limiting chemical reactions to deposit conformal, pinhole-free films in a layer-by-layer fashion. Using ALD, amorphous aluminum oxide (alumina, Al2O3) and titanium dioxide (titania, TiO2) coatings were applied to magnesium alloy (AZ-31) substrates in an attempt to inhibit corrosion. The oxide coatings and their impact on corrosion resistance were characterized using atomic force microscopy, electrochemical impedance spectroscopy, linear polarization measurements, and mechanical testing