Electrochemical Corrosion Behavior of TiN-Coated Biomedical Ti-Cu Alloy Foam in Fluoride Containing Artificial Saliva
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METAL foams exhibit a structure similar to bone and can be used as biomaterial.[1–4] Advantage of foams is their ability to provide anchorage for surrounding tissue via ingrowth of tissue into pores. Implants suffer from mismatch of mechanical properties with bone.[1–5] Ti alloys are used because of their high strength to density ratio, biocompatibility, and corrosion resistance. However, there are disadvantages such as high Young’s modulus and low wear resistance.[3–6] Ti-Cu is a heat treatable alloy by aging. Ti-Cu alloy can be used in several applications, due to lower melting point, aging possibility, and low cost of Cu. Moreover, Cu is antibacterial.[7–10] Cu addition enhances sinterability of Ti particles, and Ti-Cu compacts were sintered at lower temperatures than other Ti alloys.[11–15] Metals are sensitive to corrosion in the body. In addition, metals are bioinert. Implants must have bioactivity, strength, corrosion resistance, and toughness. Ceramics have low toughness, while metals cannot bond to bone. In order to combine mechanical properties of metals and bioactivity of ceramics, coatings were developed.[16–18] TiN has corrosion and wear resistance, biocompatibility, and can be used as coating.[18–23] Plasma spraying is the most popular TiN coating method, but it is expensive, and adherence is poor. Gas nitriding is a thermodiffusion treatment. Nitrogen diffuses and forms a compound layer. Advantages are that it does not require special equipment, and it provides high adhesion by transition diffusion layers.[18–23] Bioactive materials form bone-like apatite on their surface and bond to bone with this layer. Due to chemical
similarities, bone mineral is referred to as hydroxyapatite (HA). However, comparing with synthetic HA, bone apatite has Ca and hydroxyl deficiencies, carbonate substitution, and small crystal size. Incorporation of carbonate increases solubility, decreases crystal size.[6,24,25] Bone-like apatite can be coated on the alkalitreated Ti in simulated body fluid (SBF).[6,26] Alloys that are used in dentistry are exposed to oral environment. Saliva can cause corrosion. The pH of saliva can be in the range of 2 and 11.[27–32] Corrosion behavior of implants must be studied in artificial saliva. In oral environment, concentration of fluoride accelerates corrosion. There is increased use of dental gels containing fluoride to prevent plaque and caries. Low pH increases corrosion rate in the presence of fluoride.[9,28–33] In this study, Ti-Cu alloy foams were produced by powder metallurgy for biomedical applications. Foams were coated with TiN/TiO2 film to enhance wear and corrosion resistance. Alloys with different Cu contents were prepared to determine optimum Cu content. Cu addition decreased the melting point of the alloy. Cu addition enhanced sinterability, and compacts were sintered at lower temperatures than pure Ti. Effect of Cu addition, aging, TiN coating, pH, and fluoride content of artificial saliva on electrochemical corrosion behavior of alloys was evaluated. Metal release from specime
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