Corrosion resistance of aged Ti–Mo–Nb alloys for biomedical applications L.H. de Almeida a,⇑ , I.N. Bastos b , I.D. Santos e , A.J.B. Dutra a , C.A. Nunes c , S.B. Gabriel a,d a Universidade Federal do Rio de Janeiro, Departamento de Engenharia Metalúrgica e de Materiais, C.P. 68505, Rio de Janeiro, RJ 21.945-970, Brazil b Universidade do Estado do Rio de Janeiro, Nova Friburgo, RJ 28.625-570, Brazil c Universidade de São Paulo, Departamento de Engenharia de Materiais, C.P. 116, Lorena, SP 12.600-970, Brazil d Centro Universitário de Volta Redonda, Volta Redonda, RJ 27.240-560, Brazil e Instituto Tecnológico Vale/Vale S.A., Belo Horizonte, MG 30140-130, Brazil article info Article history: Available online 2 February 2014 Keywords: Ti–Mo–Nb alloys Electrochemical behavior Mechanical properties Biomaterial abstract Metastable b-Ti alloys combine low elastic modulus, excellent mechanical strength as well as good corrosion resistance. Wherever, the presence of nontoxic elements such as Nb, Ta, Mo, and Zr is an impor- tant advantage. With such properties this type alloy has been developed for orthopedic applications. Previous studies had shown that the Ti–12Mo–13Nb and Ti–10Mo–20Nb alloys aged at 500 °C presented higher hardness/elastic modulus ratio compared to commercially Ti–6Al–4V, indicating a great potential for biomedical application. However, additional studies are needed such as corrosion resistance. Therefore, the objective of this work was to analyze the electrochemical behavior of the Ti–12Mo– 13Nb and Ti–10Mo–20Nb alloys aged at 500 °C/24 h and 500 °C/4 h, respectively. The electrochemical behavior was carried through by potentiodynamic polarization curves in Ringer’s solutions to simulate the body fluid. The Ti–10Mo–20Nb alloy showed to be more resistant to corrosion when compared to Ti–12Mo–13Nb alloy and the commercially Ti–6Al–4V alloy. Ó 2014 Published by Elsevier B.V. 1. Introduction Titanium and titanium alloys have been used in orthopedic implants and other medical devices since the 1960s. The large acceptance of these alloys has occurred because they possess high corrosion resistance, have adequate mechanical properties, and are relatively nontoxic degradation products. In spite of the very successful use of the Ti–6Al–4V alloy of orthopedic implants, some concern remains regarding the possible toxicity of the aluminum and vanadium elements present in the alloy. In fact, due to tissular reaction, vanadium has been classified as one of the elements of the toxic group [1,2]. The possibility of vanadium ion release makes essential the development of Ti alloys without V in their composition with satisfactory properties for biomedical applications. A variety of vanadium-free or aluminum- and vanadium-free alloys have been developed, including Ti–Mo–Nb, Ti–Nb–Ta–Zr, Ti–15Sn–4Nb–2Ta–0.2Pd, Ti–12Mo–6Zr–2Fe (TMZF), Ti–15Mo, and Ti-13Nb–13Zr [3–8] and also exhibit lower elastic modulus and higher tensile properties. The alloying elements allow the stabilization of phases that affects the mechanical properties. These elements also influence the formation of a protective oxide necessary to the excellent cor- rosion resistance of these materials [3]. Indeed, the success of metallic biomaterials used in the human body can be strongly ascribed to the properties of passivation film: thin, stable, poorly soluble oxides or hydroxides when exposed to aqueous electrolyte at room temperature. When the passivation film forms, the corro- sion rate, evaluated by the anodic current density, drops to a very low value. This resistance is affected by the electrolyte condition, especially the hydrogenionic potential. The pH value is near neutrality (pH  7) for plasma, interstitial fluid, bile, and saliva; however, it is more variable (4 6 pH 6 8) in urine and very low (1 6 pH 6 3) in gastric juice [9] as well as in infectious situation. Hence, the study of film stability in physiological pH and in low pH is necessary to fully characterize the new biomedical alloys. Although titanium is thermodynamically one of the least stable structural metals in air and water, it acquires high resistance to corrosion due to a very protective titanium oxide film. Therefore, titanium–6% aluminum–4% vanadium alloy (ASTM F136 and F1472 for wrought alloys, and F1108 for castings) is commonly used in orthopedic prostheses [10]. These materials exhibit a breakdown potential in simulated body fluid well above the free http://dx.doi.org/10.1016/j.jallcom.2014.01.173 0925-8388/Ó 2014 Published by Elsevier B.V. ⇑ Corresponding author. Tel.: +55 21 2562 8510. E-mail address: lha@metalmat.ufrj.br (L.H. de Almeida). Journal of Alloys and Compounds 615 (2014) S666–S669 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom