Surface characterization, electrochemical behaviour and cytotoxicity of UNS S31254 stainless steel for orthopaedic applications Mónica Luisa Chaves de Andrade Afonso a , Ruth Flavia Vera Villamil Jaimes b , Pedro A.P. Nascente c , Sizue Ota Rogero d , Silvia Maria Leite Agostinho b,n a Instituto de Telecomunicações, Instituto Superior Técnico, Torre Norte-piso 10. Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal b Instituto de Química, Universidade de São Paulo, Av. Prof. Lineu Prestes, 748, 05508-900 São Paulo, SP, Brazil c Universidade Federal de São Carlos, Departamento de Engenharia de Materiais, via Washington Luis, Km 235, 13565-905 São Carlos, SP, Brazil d Instituto de Pesquisas Energéticas e Nucleares, Av. Prof Lineu Prestes, 2242,05508-000 São Paulo, SP, Brazil article info Article history: Received 16 October 2014 Accepted 31 January 2015 Available online 11 February 2015 Keywords: 254 stainless steel Sodium chloride Orthopaedic implants abstract The surface characterization and electrochemical behaviour of UNS S31254 (254 SS) have been performed in 0.15 mol L 1 NaCl medium in order to evaluate its application as orthopaedic implants. Polarization curves, chronoamperometry, electrochemical impedance spectroscopy and X-ray photo- electron spectroscopy were used for characterizing the samples. A cytotoxicity test was also performed to study the biocompatibility of the proposed steel as biomaterial. The electrochemical behaviour of 254 SS was compared to that observed for ISO 5832-9 and ASTM F138 stainless steels, used in orthopaedic implants. 254 SS is similar to ISO 5832-9 SS: it is passivated on the potential range between the corrosion and the transpassivation potential. Mo (VI) forms an outer layer which blocks Cr (VI) dissolution. Cytotoxicity test showed no cytotoxic character of 254 SS. & 2015 Elsevier B.V. All rights reserved. 1. Introduction Austenitic stainless steels are used as internal fixation devices. Regardless of the lower corrosion resistance when compared to titanium, they exhibit excellent mechanical properties and low cost when compared to that material [1–2]. A new generation of steels with higher corrosion resistance and improved mechanical properties is being studied [3–7]. ISO 5832-9 SS is an example of steel used in orthopaedic implants. It does not suffer pitting corrosion contrarily to F 138-92 SS [8–9]. UNS S31254 SS (254SS) is highly resistant to corrosive media, such as hydrochloric acid [10], phosphoric acid [11] and does not present pitting potential in chloride media at room temperature [10]. The viability of the scientific investigation of 254SS for this purpose is also due to its high content of nitrogen [12]. This paper reports on the electrochemical characterization of 254SS in 0.15 mol L 1 NaCl at 37 1C from linear voltammetry, chronoam- perometry, electrochemical impedance spectroscopy and X-ray photo- electron spectroscopy (XPS). Cytotoxicity test was also performed to evaluate its viability as orthopaedic implants. A comparative study between 254SS, ISO 5832-9 SS and ASTM F138 SS was also included. 2. Experimental The chemical composition of the SS samples studied is given by: UNS S31254-19.40Cr, 17.70Ni, 6.26Mo, 0.52Si, 0.208N, 0.018P, 0.016C, 0.004S; ISO 5832-9- 20.70Cr, 9.94Ni, 2.50Mo, 0.33Si, 0.32N, 0.28Nb, 0.014P, 0.015C, 0.005S; ASTM F138-92-17.60Cr, 14.20Ni, 2.08Mo, 0.26Si, 0.023P, 0.021N, 0.012C, 0.002S. The working electrodes (0.28 cm 2 area) were constructed according to previous descriptions [4]. The surface treatment of these electrodes was described elsewhere [4]. The auxiliary electrode consisted of a platinum foil and the reference electrode was the saturated calomel electrode (SCE). NaCl pa was used as electrolyte. All the experiments were conducted with naturally aerated solutions at (37.070.5)1C. The electrochemical measurements were made using equipments described elsewhere [4]. Prior to each experiment the electrodes were immersed in the electrolyte until the attainment of the stationary open circuit potential (corrosion potential E corr ). The breakdown potential (E B ) was considered when the current density was equal to 10 μA cm 2 in the potentiostatic curves. The impedance measurements were performed from 100 kHz to 50 mHz, using 10 mV amplitude. The results were modelled using Boukamp’s equivalent circuit. The samples were analysed using a Kratos XSAM HS spectrometer from the same surface treatment used for the electrochemical measurements. The technique was performed for three conditions: 1st – after polishment (600 mesh), 2nd – after application of a potential in the passive region (E ¼ 300 mV/SCE) during 20 min Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters http://dx.doi.org/10.1016/j.matlet.2015.01.157 0167-577X/& 2015 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: smlagost@iq.usp.br (S.M.L. Agostinho). Materials Letters 148 (2015) 71–75