RESUMO Com o intuito de evitar ou minimizar a corrosão por pite dos aços inoxidáveis é possível aprimorar a capacidade protetiva da camada passiva dessas ligas, e um dos métodos para se obter esse resultado é o tratamento superficial de passivação química. Nesse contexto foi investigado o efeito do tratamento de passivação química com ácido nítrico na resistência à corrosão por pite e no acabamento superficial dos aços inoxidáveis ferrítico AISI 430 e austenítico AISI 316L em meio contendo cloreto. Para isso duas condições superficiais foram utilizadas para cada material: superfície lixada e superfície passivada quimicamente conforme a norma ASTM A967/967M. O acabamento superficial foi caracterizado pela avaliação da rugosidade média e análise visual por microscopia óptica. O comportamento frente à corrosão foi avaliado através de ensaios de polarização anódica cíclica em 0,6 M NaCl conforme norma ASTM G61 e a morfologia dos pites foi caracterizada por microscopia óptica. De acordo com os resultados, a resistência à corrosão por pite dos aços inoxidáveis AISI 430 e AISI 316L submetidos ao tratamento de passivação tiveram os potenciais de pite e de repassivação aumentados em relação ao valor obtido com a superfície lixada, ou seja, tiveram sua resistência à corrosão por pite melhorada.

ABSTRACT In order to avoid or minimize the pitting corrosion on stainless steels it is possible to enhance the protective capacity of the passive layer from these alloys and one of the methods to obtain this result is the chemical passivation treatment. In this context, the effect of the passivation treatment with nitric acid on pitting corrosion resistance and surface finishing of the AISI 430 and AISI 316L stainless steels in chloride containing media was investigated. To that, two surface conditions are studied for each material: abraded surface and chemically passivated surface according to ASTM A967/967M. The surface finishing was characterized by roughness evaluating and visual analysis through optical microscopy. The corrosion behavior was evaluated by cyclic anodic polarization tests in 0.6M NaCl according to ASTM G61 and the morphology of pitting corrosion was characterized by optical microscopy. According to the results, the chemical passivation treatment had no significant effect on the surface finishing of both steels. Regarding to the pitting corrosion resistance, the AISI 430 and AISI 316L stainless steels subjected to the passivation treatment had the pitting and repassivation potentials increased in relation to the value obtained with the ground surface, that is, the pitting corrosion resistance was improved.

Nanotexturing processes that focus on enhancing the bone-implant contact, such as electropolishing, have been proposed. The aim of this work was to evaluate the influence of Ti6Al4V surface morphology on human embryonic stem cell-derived mesenchymal progenitor (hESCs-MP) growth. Three surface treatments were used in this study: mechanically polished samples and two types of electropolished samples that were treated for 4 min and 12 min, respectively. The systems were characterized by atomic force microscopy, contact profilometry, X-ray diffraction, and wettability. Each system was submitted to a cell culture containing hESCs-MP cells for 14 days, and the resultant cell growth on each system was then evaluated. The results indicated that surfaces with higher nanometric and micrometric roughnesses experienced greater hESCs-MP cell growth in osteogenic media. The same behavior was not observed for cell growth in non-osteogenic media due to the absence of dexamethasone, which is responsible for controlling protein adsorption on the surface.

AbstractSeveral studies regarding superficial treatments of Nitinol (NiTi) shape-memory have been developed aiming to the improve corrosion resistance and to block the Ni release to adjacent tissues. The necessary heat treatment to achieve the shape memory effect normally occurs at temperatures between 500 and 600 °C. However, titanium oxide (TiO2) is formed on the NiTi surface during the shape memory process heat treatment. In this work the effects of the heat treatment time on the surface characteristics of the formed NiTi oxide, at temperatures that promote the shape-memory (530 and 570 °C), were evaluated. The TiO2 layers which were obtained were evaluated by X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscope (SEM), thermogravimetric analysis (TGA), wettability and roughness. The results show that by increasing the exposure time at the temperature of 570 °C the formation of a thicker oxide is promoted, with less superficial roughness and of a hydrophobic nature. According to the literature, these characteristics indicate that the obtained oxide layer has properties that accelerat the osseointegration process.

In order to improve the NiTi alloy biocompatibility, surface treatments become very important. Nevertheless, researchers use different solutions to simulate the body fluids in electrochemical assays, and the correlation between the obtained results is difficult and might not even be possible. The present paper evaluated the electrochemical behavior of polished NiTi surfaces exposed to different simulated body fluid solutions: Hanks solution, Hanks’ balanced salt (HBSS) solution, saline body fluid (SBF) solution, and Ringer solution. The electrochemical behavior of NiTi was evaluated by open circuit potential (OCP) and cyclic voltammetry tests. The surfaces of the samples were also characterized by scanning electron microscopy, which was performed after the electrochemical tests. The results demonstrated that the NiTi alloy shows the same corrosion mechanism (pitting) in all simulated body fluids that were studied. However, the corrosion potential changes for each electrolyte, being HBSS, SBF and Ringer the most corrosive solutions. Furthermore, the Hanks and HBSS solutions demonstrated good reproducibility of the electochemical results. Considering that the HBSS represents an extreme environment, this solution seems to be the most indicated to study the corrosion behavior of NiTi treated surfaces.