Growth Kinetics of Microarc Oxidation TiO 2 Ceramic Film on Ti6Al4V Alloy in Tetraborate Electrolyte
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NTRODUCTION
TITANIUM and its alloys are extensively used in biomedical equipment, especially as hard tissue replacements such as dental implants, due to their good mechanical properties, corrosion resistance, and biocompatibility.[1,2] However, unlike bioactive ceramics, bioglass, and hydroxyapatite (HA), titanium implants cannot bond directly to the bone because of their poor osseointegration and osteoinductive properties.[3] In addition, it has been reported that metal ions released by titanium and its alloy implants can spread to the blood or muscles and then form a complex with natural
DAJUN ZHAI is with the School of Manufacturing Science and Engineering, Sichuan University, Wangjiang Campus, No. 24 South Section 1, Yihuan Road, Chengdu, 610065, Sichuan, P.R. China and also with the Material Engineering Department, Sichuan Engineering Technical College, Deyang 618000, P.R. China. KEQIN FENG is with the School of Manufacturing Science and Engineering, Sichuan University. Contact e-mail: [email protected] HUIFANG YUE is with the Nuclear Power Institute of China, Science and Technology on Reactor System Design Technology Laboratory, Chengdu 610200, P.R. China. Manuscript submitted November 18, 2018. Article published online March 14, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
proteins, causing allergic reactions.[4,5] Therefore, titanium and its alloys are surface modified before being implanted into humans. Microarc oxidation (MAO), namely plasma electrolytic oxidation (PEO) or anodic spark deposition (ASD), is an electrochemical anodizing process that employs the higher potential and discharge. This process involves anodizing above the dielectric breakdown voltage and leads to the formation of localized plasma microdischarge. Due to the increase of local temperature and pressure, plasma-chemical, thermodynamic, and anodic oxidation processes are generated at the microdischarge points, thus changing the structure, composition, and morphology of the coating.[6,7] It is reported that MAO is one of the most suitable methods to deposit a porous bioceramic layer on Ti and its alloys, which can effectively improve its biocompatibility and corrosion resistance.[3] The composition of electrolyte plays an important role in obtaining the ideal oxide coatings by MAO. The most popular electrolytes’ compositions currently used are sodium silicate, sodium phosphate, and sodium aluminates. Recent studies have shown that sodium borate (Na2B4O7Æ10H2O), which is an environmentally acceptable substance, is widely used as a metal inhibitor and an electrolyte in the MAO process to improve the coating properties.[6–13] For
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example, Zhang et al.[6] reported that the addition of borate can increase the coating thickness, but cannot further improve the corrosion resistance. Sreekanth et al.[10] demonstrated that the addition of sodium borate has a great impact on the phase transformation and greatly enhances the corrosion resistance of the MAO coating. Joni et al.[12] concluded that the rapid decompositi
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