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In the paper, the passive surface layers of AISI 304L after standard (EP50) and very-high-current density electropolishing (EP1000) in a mixture of orthophosphoric and sulfuric acids in a 1:4 ratio, are presented. The main finding of the presented studies is enrichment of the steel surface film in chromium: total chromium to total iron ratio was equal to 6.6 after EP50 and to 2.8 after EP1000; on the other hand, chromium compounds to iron compounds ratio was equal to 10.1 after EP50, and 3.9 after EP1000. [ABSTRACT FROM AUTHOR]

This work presents the nanoindentation results of two newly developed titanium alloy biomaterials, TNZ and Ti2448, after different surface treatments. The investigations were performed on the samples, AR - as received, MP - after abrasive polishing, EP - after a standard electropolshing, and MEP - after magnetoelectropolishing. The electropolishing processes, both EP and MEP, were conducted in the same proprietary electrolyte based on concentrated sulfuric acid. The mechanical properties of the titanium alloys biomaterials demonstrated an evident dependence on the surface treatment method, with MEP samples revealing extremely different behaviour and mechanical properties. Such a different mechanical behaviour may mean completely different composition and thickness of the surface film formed on the studied samples after MEP [ABSTRACT FROM AUTHOR]

Abstract: The studies of niobium after electrochemical polishing EP in sulfuric–methanesulfonic acid mixture were performed. The NbOx/Nb surface was studied by SEM/EDX and XPS methods to find out the chemical composition of the oxygen-induced structures. Specifically the XPS results obtained after EP treatment indicate prevailing part of oxygen with niobium oxides on the sample surface. In order to correctly interpret these structures the photoelectron spectra of main niobium oxides were analyzed, and the spectra of internal Nb 3d and O 1s electronic states and valence band spectra were measured for them. [Copyright &y& Elsevier]

Electropolishing is the electrolytic metal finishing process currently widely used in several high tech applications such as cardiovascular and orthopaedic body implants, pharmaceutical and semiconductor installations, superconductive niobium cavities, among others. The process provides a very clean, smooth, Beilby layer free, corrosion resistant surface. Currently, almost any metal, alloy and intermetallic compound can be electropolished, but in spite of that, we still do not have a single commonly accepted electropolishing theory. To make it even more complicated, the electropolishing process is constantly modified by addition of other physical agents and/or forces such as a magnetic field - magnetoelectropolishing, ultrasounds, or by changing the existing process parameters such as switching from direct to pulse current. The existing electropolishing theories differ in many ways from each other but possess one common ingredient, namely the viscous layer. The aim of this work is to show that the viscous layer is not an indispensible prerequisite to achieve a satisfactory electropolishing finish in every metal-electrolyte system. A supplement to the most broadly accepted electropolishing solid film theory by Hoar, namely the enhanced oxidation-dissolution equilibrium theory, is proposed. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the paper is to present the surface film composition formed on AISI 316L SS and its surface microhardeness after electropolishing (EP) and magnetoelectropolishing (MEP) in a wide range of the process conditions. The electropolishing EP process has been performed under natural convection (in still electrolyte), and under a forced convection (moderate stirring below 0.1m/s), both on the polarization plateaux and much above it. Another series of experiments was carried out on AISI 316L SS samples prepared by MEP at 350mT. The samples prepared by mechanical abrasive polishing, with the grit size up to 1000, served as a reference. First of all, concerning the surface film composition, a big difference in iron contents was observed between the samples after mechanical polishing and electropolishing. On the other hand, there were much less differentiations of chromium contents in surface film formed on 316L SS samples after each of the studied electropolishing conditions, and even mechanical polishing. The total Cr:Fe ratio was also studied, with quite promising results obtained. At the end the conclusions concerning the selection of proper electropolishing conditions have been formulated. [Copyright &y& Elsevier]

Abstract: The aim of the paper is to present the surface film composition formed on AISI 316L stainless steel after electropolishing (EP) and magnetoelectropolishing (MEP) for a wide range of the process conditions. The electropolishing EP process has been performed under natural convection (in still electrolyte), and under a forced convection (moderate stirring below 0.1m/s), both at the polarization plateaux and much above it. Another series of experiments were carried out on AISI 316L SS samples prepared by MEP at 350mT. The samples prepared by mechanical abrasive polishing, with the grit size of 1000 served as a reference. The Cr:Fe ratio was also studied for the differently prepared samples and it was found that this ratio was significantly higher for the EP and MEP samples than the mechanically polished one. Based on the results, the selection of proper electropolishing conditions have been formulated. [Copyright &y& Elsevier]

The goal of this study was to investigate the pitting corrosion resistance of AISI 316L (UNS S31603) stainless steel in Ringer's solution after electrochemical polishing of the samples in a magnetic field induced by a permanent magnet under varying induction. For the studies, the complete statistical program of investigation was adopted on the basis of the five-level compositive rotary plan. The analysis of the results obtained in this work shows that the magnetic field considerably affects the corrosion resistance of austenitic stainless steel of Type AISI 316L electropolished under varied conditions. The magnetic field introduced during electropolishing has a big influence on the pitting corrosion resistance of stainless steels. A mathematical model has been found to be an exponential regression formula Upit =f(i, B), where Upit (mV) is the pitting potential, i (A/dm2) is the current density, and B (ml) is the magnetic induction. [ABSTRACT FROM AUTHOR]

Abstract: The paper deals with the titanium biomaterial characterization after electrolytic polishing in a magnetic field in comparison with a conventional electropolishing. Both surface roughness characteristics and corrosion behaviour of Ti biomaterial wire in a physiological body fluid, Ringer''s solution, were studied. Comparison results are presented concerning surface after abrasive polishing (using the paper of grit size up to 1000) MP, standard electropolishing EP, and magnetoelectropolishing MEP. All obtained results concerning generally the titanium biomaterial surface roughness, and corrosion resistance in halide media have been considerably improved in the process of MEP and are much better than after a conventional EP. To underline the advantage of MEP process against up-to-date surface treatments, a mechanical bending test was carried out revealing much better resistance to fracture. At the end, this fatigue test has been supported by scanning electron microscopy SEM images of Ti wire biomaterial fracture. A considerable difference in fracture pattern may be observed indicating more plastic behaviour of sample after MEP. [Copyright &y& Elsevier]

Abstract: The thermodynamic stability and corrosion resistance of surface oxide layer are the most important features of stainless steels. Electrochemical polishing (EP) is the most extensively used surface technology for austenitic stainless steels. We have modified this surface technology by introducing a magnetic field to the system. With this new process called the magnetoelectropolishing (MEP) we can improve metal surface properties by making the stainless steel more resistant to halides encountered in a variety of environments. In this paper, the corrosion research results are presented on the behaviour of the most commonly used material – medical grade AISI 316L stainless steel. The corrosion investigations have been concerned on the open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and polarisation curves studies in the Ringer’s body fluid under room temperature (25°C). The X-ray photoelectron spectroscopy (XPS) was performed on 316L samples after three treatments: MP – abrasive polishing (800 grit size), EP – conventional electrolytic polishing, and MEP – magnetoelectropolishing. The comparison of the corrosion behaviour of the stainless steel’s surface after these processes was also carried out. The purpose of XPS studies was to reveal the surface film composition and the reason of this modified corrosion behaviour. It has been found that the proposed MEP process modifies considerably the composition of the surface film and improves the corrosion resistance of the same 316L SS studied. [Copyright &y& Elsevier]

A new advanced technology is proposed to obtain bare metal surfaces for peripheral stents, endodontic files and another medical devices. The effect of an externally applied magnetic field during electropolishing (magnetoelectropolishing) of Nitinol on its surface properties was investigated. The results are compared with standard electropolished Nitinol in the same electrolyte under the same process conditions. To evaluate surface properties, the following techniques were used: SEM and EDX, AFM, contact angle measurement, Auger electron spectroscopy, electrochemical impedance spectroscopy and fatigue resistance testing. All of the above analyses showed significant differences between magnetoelectropolished and conventional electropolished Nitinol surfaces. The two most prominent differences, which are likely to have the most profound implications on increased use of this intermetallic material in medical application are improved wettability and fatigue resistance. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical characteristics of L605 alloy, with various surface finishes obtained after electrolytic polishing, were investigated. This Co–Cr alloy has a clinical history in dental and orthopaedic implants and more recently in cardiovascular stent applications, where its high elastic modulus and radiopacity are desirable properties. Radiopaque materials are advantageous as they allow for better visual navigation in minimal invasive implantation procedures. For applications in the human body, surface corrosion resistance is the most important characteristic to evaluate the biocompatibility. Several studies of the corrosion resistance of Co–Cr alloy biomaterials in simulated human body fluids have been reported. The paper presents recent achievements in increasing corrosion resistance of L605 alloy after the process of electrolytic polishing in the presence of a magnetic field (MEP). [Copyright &y& Elsevier]

Abstract: The paper deals with comparison of the results obtained by electropolishing AISI 316L surfaces in an externally applied magnetic field with those of a standard electropolishing process. All electrochemical investigation methods, electrochemical impedance spectroscopy (EIS), polarization curve measurements, and surface analytical methods such as surface roughness measurements and scanning electron microscopy were carried out to determine the efficacy of electropolishing in a magnetic field. [Copyright &y& Elsevier]

This paper aims to present the preliminary results of magnetoelectropolishing, a process derived and named by application of an external magnetic field coupled with the process being controlled and maintained under oxygen evolution to achieve an electropolished surface of a workpiece. The obtained surfaces exhibit reduced microroughness, better surface wetting resulting from increased surface energy, reduced and more uniform corrosion resistance, minimisation of external surface soiling and improved cleanability. The externally applied magnetic force for use with the enhanced electropolishing process may be selected from a group consisting of either permanent magnetic or electromagnetic devices. It has been shown that the enhanced electropolishing process results in better surface performance. In the present paper, for comparison purposes, results of surface roughness, hydrophilicity and corrosion behaviour are presented. Further studies, concerning the corrosion characteristics, the morphology and surface film chemistry, are in progress. [ABSTRACT FROM AUTHOR]