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Flash butt welding is a resistance welding process that offers great advantages due to its high thermal efficiency, simplicity and high speed, makes it ideal for welding mooring chains. Despite its advantages, numerous corrosion problems are still being found in practice, both in the heat-affected zone and the weld line. Literature is scarce about it, limiting mostly to state the problem. The majority of the studies attribute this preferential corrosion to local changes in the microstructure that induce a galvanic coupling effect. Mooring chain R3 grade steel with preferential corrosion along the weld line has been studied from both metallographic examinations and electrochemical methods. Small differences were found in the microstructure of the heat-affected zone and base material (mainly composed of tempered martensite) but nevertheless, significant with respect to its corrosion behaviour. The corrosion mechanisms are discussed with particular attention to the electrochemical differences around the welding line., The authors acknowledge the financial support from VICINAY MARINE INNOVACIÓN A.I.E.

Alloy hardened steels offer excellent combination of mechanical properties, hardenability and corrosion resistance. 34CrMo4 is a medium carbon, low alloy steel widely used due to a good combination of high-strength, toughness and wear resistance. However, this steel experiences hydrogen embrittlement (HE), a complex phenomenon depending on the composition and microstructure. This work estimates de loss of the mechanical properties caused by hydrogen in electrochemically H-charged specimens in absence of mechanical stress but also, at low strain rate and constant load. H-charging for 2 and 6 h induce YS losses of about 40% and 71% and UTS losses of 39% and 59%, respectively. The synergistic effect of the stress and the H-charging process leads to a higher loss, 91%, and a faster brittle fracture even though hydrogen content is similar to those firstly H-charged and then tested in air.

Objectives Implant-related infection is one of the most devastating complications in orthopaedic surgery. Many surface and/or material modifications have been developed in order to minimise this problem; however, most of the in vitro studies did not evaluate bacterial adhesion in the presence of eukaryotic cells, as stated by the ‘race for the surface’ theory. Moreover, the adherence of numerous clinical strains with different initial concentrations has not been studied. Methods We describe a method for the study of bacterial adherence in the presence of preosteoblastic cells. For this purpose we mixed different concentrations of bacterial cells from collection and clinical strains of staphylococci isolated from implant-related infections with preosteoblastic cells, and analysed the minimal concentration of bacteria able to colonise the surface of the material with image analysis. Results Our results show that clinical strains adhere to the material surface at lower concentrations than collection strains. A destructive effect of bacteria on preosteoblastic cells was also detected, especially with higher concentrations of bacteria. Conclusions The method described herein can be used to evaluate the effect of surface modifications on bacterial adherence more accurately than conventional monoculture studies. Clinical strains behave differently than collection strains with respect to bacterial adherence. Cite this article: M. Martinez-Perez, C. Perez-Jorge, D. Lozano, S. Portal-Nuñez, R. Perez-Tanoira, A. Conde, M. A. Arenas, J. M. Hernandez-Lopez, J. J. de Damborenea, E. Gomez-Barrena, P. Esbrit, J. Esteban. Evaluation of bacterial adherence of clinical isolates of Staphylococcus sp. using a competitive model: An in vitro approach to the “race for the surface” theory. Bone Joint Res 2017;6:315–322. DOI: 10.1302/2046-3758.65.BJR-2016-0226.R2.

The investigated slow sliding speeds presented in this work enable the understanding of the wear behavior on aluminum alloys and could possibly facilitate the completion of the previously proposed wear mechanism map for aluminum at this slow sliding speed range. Dry sliding block-on-ring wear tests were carried out on aluminum alloys, AA5754 (Al-Mg), AA6082 (Al-Mg-Si), and AA7075 (Al-Zn-Cu), at a very slow sliding speed range (0.01 m/s), the specimens exhibited a wear process placed at the mild wear regime, characterized by oxidation and delamination mechanisms of both the aluminum specimen and the steel ring. However, at very slow speed range (

Nanoporous, dual and nanotubular anodic layers were grown on Ti6Al4V. Impedance spectra for nanoporous and dual revealed a response controlled by the barrier layer. Conversely, the response of the nanotubular layers depends on size of the intertubular space and immersion time. At immersion times ≥24 h, the spectra of the nanotubular layers with intertubular spaces ≤20 nm show the response of the barrier layer and the oxide covering the substrate. While for the nanotubular with intertubular spaces of ∼30 nm, the spectra show only the contribution of the substrate at the bottom of the intertubular spaces., This work was supported by Spanish Ministry of Science and Innovation under the Consolider-Ingenio 2010-CSD-2008-0023-FUNCOAT Project and under the MAT2013-48224-C2-1-R-MUNSUTI Project. Hernández-López J.M. is receptor of the JAE-predoc grant funded by the CSIC.

Laser texturing can be used for surface modification of metallic alloys in order to improve their properties under service conditions. The generation of textures is determined by the relationship between the laser processing parameters and the physicochemical properties of the alloy to be modified. In the present work the basic mechanism of dimple generation is studied in two alloys of technological interest, titanium alloy Ti6Al4V and aluminium alloy AA2024-T3. Laser treatment was performed using a pulsed solid state Nd: Vanadate (Nd: YVO) laser with a pulse duration of 10 ps, operating at a wavelength of 1064 nm and 5 kHz repetition rate. Dimpled surface geometries were generated through ultrafast laser ablation while varying pulse energy between 1 µJ and 20 µJ/pulse and with pulse numbers from 10 to 200 pulses per spot. In addition, the generation of Laser Induced Periodic Surface Structures (LIPSS) nanostructures in both alloys, as well as the formation of random nanostructures in the impact zones are discussed., This work was supported by the Spanish Ministry of Science and Innovation [SMOTI MAT2009-13751] and the Spanish Ministry of Economy and Competitiveness [MAT2013-48224-C2-1-R-MUNSUTI]. Authors also acknowledge to Professor G. Dearden from the Laser Engineering Group, University of Liverpool, for his support for this study.

Ti-6Al-4V alloy was laser textured with cross groove patterns and then coated with graphene or MoS2, evaluating its tribological behaviour. The samples were textured by a solid state Nd:Vanadate (Nd:YVO4) laser, making crossed grooves with two different crossing angles, 45°and 60° shaping a rhombus-like pattern. The percentage of surface area textured was 18, 40 and 64%. Solid lubricants were deposited by the cloth burnishing technique. Bidirectional sliding wear tests were performed to evaluate the tribological behaviour of the alloy. Lubricant working lifetimes were longer on textured and coated surfaces than on polished surfaces. Graphene presented longer lifetime than the MoS2 for 18 and 40% of textured density but rather similar for the 64%., This work was supported by the Spanish Ministry of Economy and Competitiveness [MAT2013-48224-C2-1-R-MUNSUTI]. Authors also acknowledge Prof. José Vicente García Ramos from IEM-CSIC for his insightful comments on Raman spectroscopy and Prof. G. Dearden and Dr. W. Perrie from the Laser Engineering Group, University of Liverpool, for their support in this study.

© 2015 Elsevier B.V. Friction and wear rate behaviour of dual phase steel plate specimens (DP600) sliding against corundum balls, as a function of sliding speed (0.01-0.25. m/s) and contact frequency (1-16. Hz), has been performed under bidirectional ball-on-plate (reciprocating motion) dry sliding wear tests where the plate specimen is studied. The wear mechanism is mainly oxidative. The coefficient of friction and the wear rate show not only a high dependence on the sliding speed, but also on the contact frequency which appears to be the key factor in determining the wear behaviour of DP600 even at a constant sliding speed. A thorough assesment of the wear damage as a result of energy dissipation due to friction at the interface is also carried out., The authors gratefully acknowledge the funding by Ministerio de Economía y Competitividad (MINECO) under project Innpacto IPT-020000-2010-020 and project CONSOLIDER-INGENIO 2010 CSD 2008-0023 FUNCOAT.

© 2015 Elsevier Ltd. TiO2 layers on Ti13Nb13Zr were fabricated by anodizing in acidic fluorine solution, to determine the nanostructure and electrochemical stability in a PBS solution. The anodization process showed higher growth efficiency. The morphology of nanostructured layer is more homogenous and thicker layers are obtained in shorter times regarding to organic electrolytes. Additionally, nanostructured oxide films were electrochemically studied to correlate the protective properties of the anodic films with the morphology and nanostructure developed in each anodizing condition. The anodic layers grown at short times present nanoporous structure and higher corrosion resistance than those fabricated at longer times, which possess nanotubular structure.

The effects of laser texturing on the corrosion and wettability of AA2024-T3 using an IR Nd:Vanadate picosecond (ps) laser was studied. Three types of texture patterns were generated: dimples with 5% and 50% area density (percentage of surface area textured); cross groove patterns with an area density of 64%; and concentric ring patterns with an area density of 70%. For the higher area densities, the surface character changed from hydrophilic to hydrophobic. The evolution of the open circuit potential over time, potentiodynamic polarization curves and electrochemical impedance spectroscopy were then investigated and analysed. The results revealed that ultrashort ps laser surface texturing did not modify the corrosion behaviour of AA 2024-T3 in the test solution., This work was supported by the Spanish Ministry of Science and Innovation [SMOTI MAT2009-13751] and the Spanish Ministry of Economy and Competitiveness [MAT2013-48224-C2-1-R-MUNSUTI].

Direct Metal Laser Sintering (DMLS) technique allows the manufacturing a wide variety of medical devices for any type of prosthetic surgery (HIP, dental, cranial, maxillofacial) as well as for internal fixation devices (K-Wires or Steinmann Pins). There are a large number of research studies on DMLS, including microstructural characterization, mechanical properties and those based on production quality assurance but the influence of porosity in the corrosion behavior of these materials not been sufficiently considered. In the present paper, surgical pins of Ti6Al4V have been produced by DMLS. After testing in a phosphate buffered saline solution, the surface of the titanium alloy appeared locally covered by a voluminous white oxide. This unexpected behavior was presumably due to the existence of internal defects in the pins as result of the manufacturing process. The importance of these defects—that might act as crevice nucleation sites- has been revealed by electrochemical techniques and confirmed by computed tomography., Authors wish to thank to the National Council for Scientific and Technological Development of the Ministry of Science, Technology and Innovation (CNPq/MCTI) program Ciência Sem Fronteira (400613/2013-1) and the Project 201560E004 funded by CSIC for supporting this research. X-ray tomography was done by Ms Cristina Paradela at the MNCN-CSIC.

Objectives Implant-related infection is one of the most devastating complications in orthopaedic surgery. Many surface and/or material modifications have been developed in order to minimise this problem; however, most of the in vitro studies did not evaluate bacterial adhesion in the presence of eukaryotic cells, as stated by the ‘race for the surface’ theory. Moreover, the adherence of numerous clinical strains with different initial concentrations has not been studied. Methods We describe a method for the study of bacterial adherence in the presence of preosteoblastic cells. For this purpose we mixed different concentrations of bacterial cells from collection and clinical strains of staphylococci isolated from implant-related infections with preosteoblastic cells, and analysed the minimal concentration of bacteria able to colonise the surface of the material with image analysis. Results Our results show that clinical strains adhere to the material surface at lower concentrations than collection strains. A destructive effect of bacteria on preosteoblastic cells was also detected, especially with higher concentrations of bacteria. Conclusions The method described herein can be used to evaluate the effect of surface modifications on bacterial adherence more accurately than conventional monoculture studies. Clinical strains behave differently than collection strains with respect to bacterial adherence. Cite this article: M. Martinez-Perez, C. Perez-Jorge, D. Lozano, S. Portal-Nuñez, R. Perez-Tanoira, A. Conde, M. A. Arenas, J. M. Hernandez-Lopez, J. J. de Damborenea, E. Gomez-Barrena, P. Esbrit, J. Esteban. Evaluation of bacterial adherence of clinical isolates of Staphylococcus sp. using a competitive model: An in vitro approach to the “race for the surface” theory. Bone Joint Res 2017;6:315–322. DOI: 10.1302/2046-3758.65.BJR-2016-0226.R2.

The possibility of tailoring titania nanotube films on Ti-6Al-4V alloy is investigated using electrolytes based on NH4H2PO 4 with the addition of different concentrations of NH4F. Several morphologies from high aspect ratio nanotubes to barrier layers are achieved by the control of the electrolyte composition, regarding its pH and fluoride concentrations. The morphology and composition of the anodic layers were evaluated by scanning and transmission electron microscopy, Rutherford backscattering spectroscopy (RBS) and Wavelength dispersive X-ray fluorescence spectroscopy. The formation efficiency and the fluoride ions content in the nanotubes depend on the F concentration in the electrolyte. The higher concentration of fluoride ions in the electrolyte promotes an increase of the F incorporated in the nanotubes, about 12 at.% but, reduces the nanotube formation efficiency. However, no significant presence of phosphorus was detected into the films by means of the above-mentioned analytical techniques. © 2011 Elsevier Ltd. All rights reserved.

Durante la pasada década se han empleado diferentes técnicas de modificación superficial para mejorar la biocompatibilidad de la aleación de NiTi con memoria de forma. Este trabajo se centra en el estudio de la influencia del N implantado con una energía de 150 keV y con dosis nominales comprendidas entre 0.5x1017 to 8x1017 ion cm–2, en el comportamiento frente a la corrosión del NiTi en solución de Hank. Se han realizado medidas de nanodurezas y de resistencia a la corrosión mediante curvas de polarización potencio-dinámicas y espectroscopía de impedancia electroquímica, así como los cambios en composición promovidos en la superficie se evaluaron mediante XPS. Los resultados de dichos ensayos revelaron una mejora en la resistencia a corrosión del comportamiento para las muestras implantadas con una dosis de N de 2x10–17 ion•cm–2 y un aumento de la nanodureza y de la rigidez superficial con la dosis implantada

Polypyrrole coating was successfully deposited on anodized 2024 unclad aluminum alloy showing that the presence of the anodic film is the key factor to ensure better adhesion to the polymer coating. Corrosion resistance of the conductive polymer layers grown for three and five cycles were evaluated in a 3 wt.% NaCl solution using polarization curves and impedance spectroscopy. It was found that the thermally treated polymer coating with higher thickness (five cycles) exhibited the best corrosion performance. This best coating shifts the corrosion potential towards nobler values, about 650 mV, and the exchange current density decreases two orders of magnitude regarding the anodic layer. The partial reduction of the structure of the polymer promoted by the thermal treatment plays a key role in the corrosion resistance of the coating allowing to the thermally treated polymer layer to act as a physical barrier against corrosion. © 2007 Elsevier B.V. All rights reserved.

The preparation and properties of protective sol-gel coatings on metallic substrates are reviewed. Control of the coating microstructure is critical to obtain the desired properties and this requires optimisation of processing parameters that include sol composition, synthesis and processing conditions, deposition method and post-deposition sintering or curing. Current knowledge in these areas, e.g. structure-property-processing relationships, and the characterisation of the coatings produced are discussed. SiO2 layers have been found to confer good oxidation resistance, but for electrochemical corrosion resistance, mixed oxide layers or hybrid organicinorganic layers are required. Incorporation of alkylalkoxides with polymerisable groups attached has allowed synthesis of hybrid nanostructured coatings consisting of interpenetrating, chemically bonded organic and inorganic networks. Doping of hybrid sol-gel coatings with environmentally friendly inhibitors is also a promising approach combining barrier properties with active inhibition of corrosion. The potential to control functional properties such as biocompatibility is also briefly considered. It is concluded that both fundamental work on new coating compositions and the development of improved industrial technologies are priorities for future research. © 2007 Institute of Materials, Minerals and Mining and ASM International.

The meat casing industry works with highly fibrous materials and low pH conditions. The pumps propelling the gel must therefore be highly corrosion-erosion resistant. In fact, the most common failure in this medium is corrosion, erosion or, most commonly, a combination of both. Coatings are thus required to protect the pump surface and maintain the operational conditions. TiN-PVD coatings seemed to be an attractive alternative amongst the range of options to extend pump lifetime. However, despite the greater chemical inertia expected of TiN, the combined effect of corrosion and erosion can induce a fast attack on the material. The present paper analyses failure of a TiN coating with a single-layer configuration in contact with an edible slurry of collagen used in the meat casing industry. The degradation mechanism comprises two different steps. Firstly, the acidic components reach the base steel through the pores, promoting severe dissolution of the steel substrate and leaving the TiN coating without support. Secondly, the coating detaches under working conditions and merges with the casing solution. Finally, the fibres together with the hard particles erode the pump walls, leading to fast deterioration. © 2006 Elsevier B.V. All rights reserved.

© 2015 Elsevier Ltd. All rights reserved. Friction and wear rate behaviour of dual phase steel discs (DP600) have been studied as a function of sliding speed (0.5-1.25 m/s) and contact frequency (3.5-8.5 Hz) under unidirectional and bidirectional (reversal motion) ball-on-disc dry sliding wear tests. The wear rate is found to be higher under unidirectional sliding. The Bauschinger effect - BE-appears to take place during the bidirectional sliding processes. However, it is only evident when the sliding direction is reversed for some limited times, where the mass loss decreases accompanied a weakened strain-hardening effect. Moreover, the BE in the DP600 steel discs is also affected by both the sliding speed and the contact frequency, but its effect is clearly different., The authors gratefully acknowledge the funding by Ministerio de Economía y Competitividad (MINECO) under project Innpacto grant number IPT-020000-2010-020 and project CONSOLIDER-INGENIO 2010 grant number CSD 2008-0023 FUNCOAT.

© 2015 Elsevier B.V. All rights reserved. The use of osteoarticular implants has improved the quality of life of millions of patients. In this work nanotubular structures tailored made on Ti6Al4 V substrates was used as drug delivery system of ibuprofen as a proof of concept. Three different nanotubular films with different sizes and forms (NT, NT+ and NTb) were analysed. Samples were soaked in a solution of 660 mg ibuprofen/20 mL n-pentane. The ibuprofen release in aqueous medium was evaluated by liquid chromatography reversed-phase (RP-HPLC). To calculate the observed constant k, the amount of ibuprofen released was plotted versus the time using linear regression according to the zero-order, first-order, second-order and Higuchi model. The release of ibuprofen was constant and independent of the concentration. The kinetic constant obtained was 0.021 (NT), 0.022 (NT+) and 0.013 (NTb) being the correlation factor of 0.98 (zero-order) where the maximum correlation factor was reached. These results indicate that the delivery process from NT and NT+ is similar and slower that NTb. In all the cases was inside the therapeutically range. These results showed the potential of these modifications in order to develop implants that can carry different molecules of medical importance., This work was funded by the grants from the Spanish MICINN (CS02010-11384-E, MAT2012-35556) and MINECO (MAT2013-48224-C2-2-R and MAT2013-48224-C2-1-R).

© 2015, Copyright © Society of Tribologists and Lubrication Engineers. The investigated slow sliding speeds presented in this work enable the understanding of the wear behavior on aluminum alloys and could possibly facilitate the completion of the previously proposed wear mechanism map for aluminum at this slow sliding speed range. Dry sliding block-on-ring wear tests were carried out on aluminum alloys, AA5754 (Al-Mg), AA6082 (Al-Mg-Si), and AA7075 (Al-Zn-Cu), at a very slow sliding speed range (0.01 m/s), the specimens exhibited a wear process placed at the mild wear regime, characterized by oxidation and delamination mechanisms of both the aluminum specimen and the steel ring. However, at very slow speed range (, The authors gratefully acknowledge funding from the Ministerio de Economıa y Competitividad and Fondo Europeo de Desarrollo Regional (FEDER) under project Innpacto IPT-020000-2010-020 and project CONSOLIDER-INGENIO 2010 CSD 2008-0023 FUNCOAT.

Corrosion and tribocorrosion studies of a TiBxCy/a-C coating deposited on AISI 316L steel have been performed in an aqueous solution of 0.26 vol.% acetic, 0.16 vol.% peracetic and 0.18 vol.% hydrogen peroxide (commercial product Oxonia 1 vol.%). The corrosion current density of the TiBxCy/a-C coating ranges on the same order as bare steel but with a significantly decreasing friction (0.1 vs. 0.6) and wear rate (~ 10 times lower). The compact microstructure of the coating hinders the access of the aggressive electrolyte to the substrate, preventing the onset of the corrosion attack, while maintaining an excellent tribological behavior in strong oxidant solutions.

© 2015 Elsevier Ltd. All rights reserved. Friction and wear rate behaviour of dual phase steel discs (DP600) as a function of sliding speed (0.05-3.75 m/s), and contact frequency (0.6-16.5 Hz) have been studied under unidirectional ball-on-disc dry sliding conditions. The coefficient of friction (COF) and wear rate exhibit not only a highly dependence on the sliding speed, but also on the contact frequency which appears to be the key factor determining the wear behaviour of the DP600 even at constant sliding speed. The wear mechanism is mainly oxidative. The validity of Garcia-Ramil-Celis model is demonstrated for discontinuous sliding contacts at contact frequencies below 7 Hz. However, above 7 Hz, the disc behaves as if it were subjected to a continuous sliding contact., The authors gratefully acknowledge the funding by Ministerio de Economía y Competitividad (MINECO) under project Innpacto IPT-020000-2010-020 and project CONSOLIDER-INGENIO 2010CSD 2008-0023 FUNCOAT.

CrN multilayer coatings are possible replacements for hard chromium because of their good mechanical and chemical properties. This paper focuses on X-ray photoelectron spectroscopy (XPS) to study the mechanism of electrochemical stripping of multilayered Cr-N based coatings. The samples were produced by electron beam (e-beam) physical vapour deposition (PVD), on mirror polished M2 steel. Multilayers constituted three separate layers of CrN with intermediate interlayers of Cr (0.1 μm). The total coating thickness was in the range 4.5-5.5 μm. Under galvanostatic conditions, anodic oxidation of CrN leads to replacement of nitrogen in the CrN coating by oxygen, forming oxy-nitrides on the samples surface. Contrary to findings described by some authors, we have not detected Cr6+ in this research. © 2006 Elsevier B.V. All rights reserved.

The present paper analyses the performance of CrN single-layers produced by electron beam PAPVD (EBPAPVD), finding that both corrosion and wear resistance are directly dependant on the structure and stoichiometry of the nitride. The nanolayer structure of the coatings is formed by periodically varying the nitrogen pressure during deposition resulting in layers with higher and lower N-content. This fact, which has not been described in the literature, causes different structure and morphology of the individual films providing excellent properties to the coating. For corrosion resistance, the CrN layer's greater compactness impedes penetration of the electrolyte and thus prevents the formation of a galvanic couple between the coating and the substrate. Moreover, a good wear resistance is obtained, retarding its delamination. © 2006 Elsevier B.V. All rights reserved.

The corrosion mechanism of commercially galvanised steel (containing Pb) in sodium chloride solution was evaluated using electrochemical impedance spectroscopy and polarisation curves. The behaviour of the system was simulated by an equivalent circuit with two time constants, including a Warburg element to consider the diffusion process at longer immersion times. To begin with, the impedance measurements indicated a non-stationary system with two time constants which could be related to the charge transfer resistance and the adsorption of the intermediate species. With increasing immersion time, the impedance spectra showed a corrosion mechanism that is under activation control. With immersion times of up to one month, the influence of diffusion processes on the overall corrosion mechanism increases significantly.

In this work, the influence of the processing conditions on the microstructure and abrasive wear behaviour of a NiCrBSi hardfacing alloy is analysed. The hardfacing alloy was applied in the form of coatings onto a mild steel substrate (Fe-0.15%C) by different techniques: laser cladding (LC) and flame spraying (FS) combined with surface flame melting (SFM). In both cases, the appropriate selection of the process parameters enabled high-quality, defect-free NiCrBSi coatings to be obtained. The microstructure of the coatings was analysed by scanning electron microscopy (SEM), with attached energy dispersive spectroscopy (EDS) microprobe, and by X-ray diffraction (XRD). Their tribological properties were evaluated by micro-scale ball cratering abrasive wear tests using different abrasives: diamond, SiC and WC. Microstructural characterisation showed that both coatings exhibit similar phases in their microstructure, but the phases present differ in morphology, size distribution and relative proportions from one coating to another. Wear tests showed that in three-body abrasive conditions, despite these microstructural differences, the wear behaviour is comparable for both coatings. Conversely, in two-body wear conditions with diamond particles as the abrasive, it was observed that the specific wear rate of the material is sensitive to microstructural changes. This fact is particularly apparent in LC coatings, in which the zones of the layers with higher proportions of very small hard particles present a lower wear resistance. These results indicate that it is important to have good microstructural control of this material, in order to obtain coatings with an optimized and homogeneous tribological behaviour. © 2005 Elsevier B.V. All rights reserved.

The corrosion mechanism of galvannealed in 0,6 M NaCl has been evaluated by means of electrochemical impedance spectroscopy (EIS). After 48 hours and for longer immersion time, up to 1 month, in sodium chloride, the system is controlled by a diffusion process at finite layer. Moreover, the effectiveness of cerium salts as inhibitor added in the electrolyte has been studied. Inhibition percentages of about 85% for 500 and 1000 ppm at 24 hours have been found. On the hand, changes in the corrosion mechanism due to the cerium presence were shown.Se ha estudiado el mecanismo de corrosión de un acero galvanorrecocido, en 0,6 M de cloruro sódico, mediante espectroscopia de impedancia electroquímica. Los resultados revelan que el sistema, para tiempos mayores de 48 h de inmersión y hasta 1 mes en NaCl, está controlado por un proceso de difusión en capa finita. A su vez, se ha estudiado la efectividad de sales de cerio como inhibidor añadido en el medio agresivo, obteniéndose porcentajes de inhibición del 85% para concentraciones de 500 y 1.000 ppm a las 24 h de exposición. Además, los espectros de impedancia electroquímica revelan un cambio en el mecanismo de corrosión del galvanorrecocido por la adición del cerio en el medio.

Galvanized reinforcing steel with a cerium conversion coating have been studied in Ca(OH)2 saturated solution with and without chlorides. Electrochemical results reveal that cerium conversion coating provides an effective corrosion resistance compared to galvanized steel at short immersion times, 5 days without Cl- ions and 2 days with Cl- in the solution. The results suggest that cerium layer inhibits hydrogen evolution on the galvanized coating at early stages. At longer immersion times, galvanized steel with cerium conversion coating and galvanized steel describe similar corrosion behaviour in both electrolytes. There is not significant differences in the corrosion current density, about 5 μA/cm2, due to the presence of chlorides ions in the Ca(OH)2 saturated solution up to approximately 17 days of immersion. At longer immersion times, from 30 to 50 days, specimens in the chlorides containing solution exhibit higher corrosion activity than that recorded in the free Cl- solution revealing that cerium layer cannot inhibit the localized attack promoted by chloride ions. © 2006 Elsevier Ltd. All rights reserved.

The laser cladding of diesel engine exhaust valves is an emerging technology that provides excellent results in terms of the wear and corrosion resistance of the repaired materials. This work focuses on the deposition by laser cladding of Stellite 6 alloy coatings on two different base materials: an AISI 1045 carbon steel and an AISI 304 stainless steel. Following a process optimisation criterion, several of the fundamental laser treatment parameters were varied in order to obtain defect-free coatings with good adherence and minimal dilution. The metallographic structure of the clad material, irrespective of the substrate used, consists of a typical dendritic microstructure in a solid solution of Co. The mechanical strength of the layers was analysed by measuring HV0·1 microhardness and sliding wear behaviour. Laser coatings achieved hardness greater than 500 HV0·1, and presented excellent dry sliding wear behaviour, with a dimensional wear coefficient k one and a half orders of magnitude lower than that of the substrates. A combined oxidation and abrasion mechanism dominated the wear of the Stellite 6 layers, while in the case of AISI 1045 steel substrate, the wear was caused mainly by a surface oxidation mechanism. For the AISI 304 steel, the wear resulted from a combined adhesion, abrasion and plastic deformation mechanism. © 2006 Institute of Materials, Minerals and Mining.

The present paper investigates the inhibition mechanisms of CeCl3·7H2O in a range of concentrations, 100-1000 ppm, on hot dip galvanised steel in 3.5 wt.% NaCl solution. Following 4 h immersion in the studied solution, galvanised steel develops a yellow layer on the surface. X-ray photoelectron spectroscopy (XPS) revealed that the layer is composed of two regions: a surface region, which is a mixture of a hydrated oxide/hydroxide of cerium (III) and ZnO, and an internal region, which is a mixture of ZnO and cerium (III) oxide. © 2004 Elsevier B.V. All rights reserved.

[ES] El presente trabajo se centra en la obtención de capas de aleación base Cobalto (Tribaloy T-800) sobre un sustrato de acero inoxidable 18/8 (AISI 304) mediante la técnica de plaqueado láser. Tras los tratamientos, se caracterizaron las probetas mediante microscopía óptica y electrónica de barrido con microanálisis (EDS). La composición elemental del recubrimiento se determinó en un espectrómetro de emisión óptica con fuente de excitación (GDL). El estudio de la interfase reveló una perfecta adherencia entre el recubrimiento y el material base, sin defectos apreciables. La microestructura de las capas depositadas es dendrítica con un alto grado de refinamiento y una homogeneidad química a lo largo del cordón y con valores muy próximos a los del polvo de partida. En las zonas de solape entre cordones, se observó un crecimiento del grano debido al segundo tratamiento térmico recibido. La microdureza de las capas alcanza los 750 HV, valor considerablemente superior al del sustrato (200 HV). Asimismo, se obtuvo una mejora significativa de la resistencia a la corrosión del recubrimiento en medios salinos., [EN] The present work is based on obtaining Co based coatings (Tribaloy T-800) on plates of 18/8 stainless steel (AISI 304) by laser cladding technique. After the treatment, samples were characterized by optical and scanning electron microscopy with EDS analysis. The elemental composition of the coating was determined with a glow discharge lamp spectrometer (GDL). The study of the interface revealed a good adherence between the substrate and coating without substantial defects. For the laser cladded coatings, the microstructure was dendritic with a high degree of refinement and chemical homogeneity close to the original powder. The grain coarsening was observed in the overlapping zones due to the second heat treatment. Microhardness of the coatings reached 750 HV, a considerably higher value than the substrate hardness (200 HV). Also, the coating corrosion resistance in saline solutions had a great improvement., Al Proyecto del Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica 2000-2003, de referencia: MAT2001-3528-C03-02 de título: Optimización frente al desgaste y la corrosión de recubrimientos de NiCrBSi depositados por flame spray y láser.

In recent times, a good deal of research efforts have been devoted to develop new environmentally friendly corrosion inhibitors as an alternative to the classic systems based on chromates. In this way, rare earth salts have demonstrated a high efficiency in different metal/corrosive systems. Lanthanide salts are classified as cathodic inhibitors, although, it is not clarified the species which contribute to the formation, in the cathodic areas, of the oxide/hydroxide of the lanthanide ion. In this work, the inhibitor behaviour of CeCl3 for galvanised steel in aerated NaCl solutions has been investigated. SEM and EDS studies showed that Ce is initially stochastically dispersed onto the metallic surface, forming a continuous film on its surface after prolonged immersion time. Electrochemical calculations seem to indicate that, under experimental conditions only Ce3+ is expected on the metallic surface and this is consistent with experimental findings. © 2003 Elsevier Ltd. All rights reserved.

Surface hardening thermo-chemical treatments provide metallic alloys with very hard corrosion and wear resistant coatings. As the layers obtained are so thin that dissuade from any machining operation after the treatment, it is useful to evaluate possible dimensional changes. This work studies the dimensional stability of alloy Ti6A14V after gas nitriding at 1100 °C and of superalloy MA956 after surface oxidation at the same temperature. For reference purposes, an analysis is also made of the deformations that appear on steel after conventional pack carburising treatment. In this study flat test specimens of 3 mm thickness were used, each of which had central drilled holes surrounded by six smaller outlying drilled holes. A calculation program allows the determination of changes in the drilled hole diameters and in the position of their centres as a consequence of the treatment. © 2002 Elsevier Science Ltd. All rights reserved.

Ti-Al intermetallic coatings on titanium have been produced by laser surface alloying. A 5-kW CO2 laser was employed to melt the surface of the titanium specimens and to alloy it with aluminium powder in a nitrogen atmosphere. The combination of titanium, aluminium and nitrogen and the specific characteristics of the high-power laser allow a new coating structure of titanium aluminides and nitrides to be produced. These coatings present a surface Al-TiAl3 composition that gradually evolves to Ti3Al close to the titanium base. A dendrite structure of titanium nitrides (TiN and Ti2N) and titanium aluminium nitrides (Ti2AlN) is formed throughout the laser track. The different structures obtained are described as a function of laser energy input during the process. © 2002 Elsevier Science B.V. All rights reserved.

Stellite layers produced for protective coatings in a direct process by laser remelting of the powder SF6 on plates of a high-temperature resistive alloy in Ar environment are investigated experimentally. Microphotographs and EDS analysis reveal a metallurgical bond between the substrate and coating as well as the structural homogeneity along the depth of the layer which is characterised by a chemical composition close to that of the powder. The laser-clad layers show a dendritic and fine-grained structure with a minor presence of impurities. For the coatings an improvement of mechanical properties in comparison to the base material such as the behaviour in wear resistance comparable to that of TiN and values of microhardness up to approximately 1000 HV are observed. On the other hand, corrosion properties depended on the defects and appeared on the surface as a result of the laser process parameters. © 2002 Elsevier Science Ltd. All rights reserved.

Inhibitors are probably the oldest method of corrosion protection. In the late 1980s, legislation forced research into environmentally friendly corrosion inhibitors combining low toxicity with high efficiency. Rare earth metal (REM) compounds are a promising type of environmentally friendly inhibitors. The mechanism of action of the lanthanide salts for different materials is a consequence of blocking the cathodic areas by precipitation of a film of lanthanide oxide/hydroxide. The trivalent ions of rare earths in an aqueous solution undergo progressive hydrolysis to form complex hydroxylated ions. The composition depends on the lanthanide cation and the particular anion of the solution.

© The Royal Society of Chemistry 2014. Titanium anodic oxide layers with a bottle shaped nanotubular structure have been grown in an electrolyte containing NH4F, applying voltage steps. The grown layers were analyzed using scanning and transmission electron microscopy (SEM and TEM), and Rutherford backscattering spectroscopy (RBS). The results show that a concentration of 0.15 M of NH4F in the anodizing bath, and a step of 10 to 20 V produces an oxide with a double morphology comprised of nanotubes at the oxide/metal interface and nanopores at the oxide/electrolyte interface of the anodic layer. Higher concentration of F- in the bath, 0.3 and 0.45 M NH4F, enhanced the chemical dissolution of the anodic layer resulting in nanotubular structures along the oxide layer. Therefore, the bottle shaped nanotubular structures that show a well defined morphology are obtained in a bath containing a concentration of 0.3 M NH4F and applying a voltage step of 10-20 V.

© 2014 Elsevier B.V. Functionalization of the Ti6Al4V alloy by combining laser texturing and anodizing has been performed. The laser texturing was carried out with a Q-switched Nd:YAG laser using 1064nm and an energy of 90mJ/pulse. After the laser treatment, nanostructured titanium anodic oxide layers have been grown in an aqueous electrolyte (H2SO4+HF). The topography and the surface morphology of the laser textured alloy without and after anodizing were characterized using an optical imaging profiler and a scanning electron microscopy (SEM), respectively. Changes in wettability and the electrochemical stability of the modified surfaces have been also analyzed. The results show that the consecutive use of both processes allows changing the topological pattern thus developing a micro-nano topography that could selectively promote tissue cell attachment. While laser texturing promotes an important increase in the roughness due to the generation of dimples on the surface, the anodizing process fabricates a homogeneous nanoporous titanium oxide layer that it turns the surface hydrophilic. Moreover, corrosion resistance of the laser textured surface can also be improved due to the better chemical stability of the nanostructured oxide layer formed on the surface.

Electrochemical noise has been used to study the tribocorrosion behaviour of austenitic stainless steel AISI 316 in two different simulated body fluid solutions [phosphate buffer solution (PBS) and PBS plus bovine serum albumin). The analysis of potential and current transients permits not only the determination of the contribution of the aggressive medium to the total volume loss due to synergism between wear and corrosion but also the detection of changes in the mechanism produced by the mechanical/electrochemical attack. © 2014 Institute of Materials, Minerals and Mining.

Mediante nitruración gaseosa a elevada temperatura de la aleación Ti6Al4V se han obtenido capas de nitruro de titanio que mejoran sus características superficiales. Con vistas a la aplicación como biomaterial se ha estudiado el incremento de dureza, la resistencia al desgaste y la adherencia de dichas capas al substrato. Se ha diseñado un sistema de medida de la adherencia de la capa nitrurada al metal base mediante flexión controlada en puente de carga. La caracterización de los constituyentes de las capas obtenidas se ha realizado mediante difracción de rayos X, metalografía óptica y SEM. Se ha logrado obtener unas capas de nitruro de titanio con durezas superiores a los 700 Vickers, que confieren al material una buena resistencia al desgaste.

Exfoliation is a type of attack that appears in rolled and extruded products, causing great losses of surface material due to the effect of delamination. Until now, the surface inhomogeneity promoted by this attack has been analysed using microscopic observation techniques. In this work, the electrochemical impedance spectroscopy technique has been used to characterise the exfoliation corrosion susceptibility of two light aluminium alloys. Some correlation between changes in the specimen's surface morphology and variations in the shape of Nyquist and Bode diagrams were found, making it possible to determine the stage of attack promoted on the material. (C) 2000 Elsevier Science Ltd. All rights reserved. | Exfoliation is a type of attack that appears in rolled and extruded products, causing great losses of surface material due to the effect of delamination. Until now, the surface inhomogeneity promoted by this attack has been analyzed using microscopic observation techniques. In this work, the electrochemical impedance spectroscopy technique has been used to characterize the exfoliation corrosion susceptibility of two light aluminum alloys. Some correlation between changes in the specimen's surface morphology and variations in the shape of Nyquist and Bode diagrams were found, making it possible to determine the stage of attack promoted on the material.