Effects of Substrate and Electrodeposition Parameters on the Microstructure of Hydroxyapatite Coating

Abstract

Background: Hydroxyapatite (HA) has been widely used in hard-tissue repair applications, such as implant coatings and bone substitutes, because of its stability under in vivo conditions and its osteoconductivity. Objectives: The aim of this study was to investigate the effects of HA coating applied on two different metallic materials that are used as implants, with regard to the substrate and electrochemical parameters of their microstructure. Materials and Methods: HA coating was applied on AZ31 magnesium alloy and stainless steel 304, metallic materials used as implants, and the effects of the substrate and electrochemical parameters on their microstructure were investigated. Results: It was observed that at 2 V potential and 85°C for AZ31 and steel 304, the coatings did not have proper coverage and the grains were coarse. By hindering the grain growth, complete coverage with a uniform and fine structure will be achieved. There was a difference in morphology that was probably due to the different open circuit potentials of these two alloys. Magnesium alloys have more negative potential, in which H2 formation can hinder growth of HA flakes, but in Ti base alloys, the formation of H2 gas does not easily form in the working potential, so the HA coating can grow easily. Conclusions: Nanosized HA coating can be obtained on stainless steel 304, AZ31 magnesium alloy, and Ti-6Al-4V by cathodic deposition using pulse and direct cathodic electrodeposition from a proper electrolyte solution, regardless of the substrate material.