Effect of Coating Method on the Surface Characteristics of NiTi Shape Memory Alloy

Abstract

Metallic materials including stainless steel, cobalt-chromium alloys, titanium and its alloys, and nickel-titanium (NiTi) shape memory alloys have been used in biomedical applications since the 1940s due to their favorable mechanical properties. Classified as a smart material, NiTi alloy has gained noticeable popularity in biomedical fields such as orthopedic, dental, and cardiovascular applications as it retains reasonable corrosion resistance and biocompatibility along with unique shape memory properties. However, several studies have shown their limits in medical applications due to the risk of Ni ions release from the NiTi implant surface. In order to prevent Ni release, ceramic-based surface coatings such as hydroxyapatite, alumina, and titanium dioxide have been proposed applied by various methods such as electrophoretic deposition, sol-gel, biomimetic and dip coating. In this work, HA coatings on NiTi wire samples were obtained by using biomimetic and dip-coating methods. The biomimetic coating consisted of immersing the NiTi wire samples into simulated body fluid for 24 and 48 h periods, whereas dip coating was accomplished by placing the NiTi wire samples into the HA suspension and retracting the sample with a controlled speed. The effects of the two coating methods on coating quality, surface characteristics and corrosion behavior of NiTi wire samples were investigated. Dip coating method was shown to be a more favorable technique for the NiTi wire samples used throughout this study.