Improved Hardness and Tribocorrosion Properties of Nickel Coatings by Co-Depositing ZrO2 MicroSized Dispersed Phase During Electroplating Process

The tribocorrosion properties of ZrO2 – nickel microstrucured composite coatings have been studied in the following conditions: - Solution: 0.5 M K2SO4; - Tribo corrosimeter: pin on disc connected with electrochemical cell; - Normal Force: 10 N; - Rotation Speed: 120 tours/min. The objectives of our study in principal are to fully understanding the tribocorrosion process kinetic and mechanism of composite coatings materials. The samples with coating on a top of a cylinder were installed in a cell, containing the electrolyte and electrodes, and mounted on a pin-on-disc tribometer, with the working surface of the specimen facing upwards. The counterbody (pin) was a corrundum cylinder (7 mm in diameter), mounted vertically on a rotating head, above the specimen. The lower spherical end (radius = 100 mm) of the pin, was then applied against the composite surface (disc) with an adjustable normal force. When rotation was applied, the end of the pin draws a circular wear track (16 mm in diameter) on the working composite surface. Both continuous and intermittent friction tests were carried out. In the intermittent tests, friction was applied periodically: during each cycle, friction was first applied for 2 seconds at 120 rpm (sliding speed 100 mm/second) under 10 N (average pressure 120 MPa for hertzian contact conditions) and then stopped during a latency time (20 or 200 s.). This mechanical solicitation was repeated over 2500 cycles. Some features of these tests reproduce the wear conditions of composite coatings in the intermittent friction, K2SO4 0.5 M was used as corrosive and passivating electrolyte for tribocorrosion tests

Study of Zro2/Co-Deposition with Cobalt from Chloride Electrolyte

The metal-matrix composites are materials in which the properties of a metallic host material are modified with addition of a second phase (ceramics) by electrodeposition process. The second phase can be hard oxides or carbides particles or diamond, or solid lubricants or even liquid containing microcapsules. Most composite coatings contain micron-sized particles. The major challenges with the codeposition of second phase particles are the achievement of a high level of codeposition and avoiding the agglomeration of particles suspended in the electrolytes. The poorly homogeneous distribution of second phase particles in the metallic matrix can be detrimental to the mechanical properties. This work shows the most recent results regarding the influence of ZrO2 bioceramic dispersed in the cobalt matrix during electroplating process from a chloride cobalt electrolyte. The ZrO2/Co composite coatings were electrodeposited from a suspension of ZrO2 particles (mean diameter 10 μm) in aqueous cobalt chloride electrolyte. Suspension was prepared by adding 20 g/L ZrO2 particles into solution. Co-deposition of dispersed micro sized particles with cobalt during electroplating process influences the structure and surface morphology of composite coatings obtained. The pure cobalt coating has a rather regular surface, whereas the composite coatings surface has fine different disturbed structure. The composite coating thickness increases with increasing the current density, whereas the content of ZrO2 particles inside the cobalt matrix decreases with current density

Corrosion behaviour of titanium in the presence of Streptococcus mutans

Objective The main aim of this in vitro study was to evaluate the influence of Streptococcus mutans on the corrosion of titanium. Methods S. mutans biofilms were formed on commercially pure titanium (CP-Ti) square samples (10 mm × 10 mm × 1 mm) using a culture medium enriched with sucrose. Open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements were used to evaluate the corrosion behaviour of CP-Ti in the presence of S. mutans in Fusayama's artificial saliva. The corrosion of biofilm-free CP-Ti samples was also evaluated in artificial saliva. Biofilms biomass was measured by spectrophotometry, using crystal violet staining, after 1, 2 and 7 days. Results The OCP values recorded on CP-Ti in the presence of S. mutans (−0.3 ± 0.02 V vs. SCE) was lower than those on biofilm-free CP-Ti (−0.1 ± 0.01 V vs. SCE) after 2 h of immersion in artificial saliva (p < 0.05). That reveals a high reactivity of titanium in presence of S. mutans. Impedance spectra revealed the formation of a compact passive film on titanium in artificial saliva or in the presence of a 2 days old S. mutans biofilm even though the corrosion resistance of CP-Ti has decreased in presence of a S. mutans biofilm. Conclusion The presence of bacterial colonies, such as S. mutans, negatively affected the corrosion resistance of the titanium.The authors acknowledge the financial support provided by Alban Programme (cod. E06D103407BR), the Erasmus Student Exchange Programme of the CEC, FCT (PTDC/CTM/67500/2006) and the Scientific Research Community on Surface Modification of Materials funded by the Flemish Science Foundation (WOG-FWO-Vlaanderen)

Tribocorrosion: Material behavior under combined conditions of corrosion and mechanical loading

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Synergism in tribocorrosion: state-of-the-art, recent approaches, and assessment on stainless steel and complex metallic alloys

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Tribo-electrochemical impedance: A new technique for mechanistic study in tribocorrosion

International audienceOn the basis of a classical model of triboelectrochemistry, a new approach is proposed based on an impedance ratio of a mechanical perturbation and an electrochemical response. Theoretical derivation, experimental setup and application to a passive stainless steel in a borate solution are presented. Transient characteristics yielded by the technique, associated to a permanent tribological regime, are found to obey a two-time-constant law. They are discussed and compared to the global repassivation transients of the material after switching off the abrasive friction

Nanotribology on individual phases of duplex steel: combining roughness, material effects, and friction

International audienceIn this study, lateral force microscopy (LFM) technique was used to investigate local friction and wear behaviour on individual phases of dual phase steel. Important factors influencing friction interpretation at nanoscale are investigated. A nanoprobe made of silicon nitride (20 nm tip radius) was used for this investigation. The difference in phases is clearly apparent when the surface is smooth but with a slight increase in surface roughness, the frictional difference between the phases got masked. A clear direct dependence of friction force on normal force was observed at nanoscale as predicted by Derjaguin's friction model. This model appeared to be valid irrespective of the surface roughness modifications on different phases of the material. The tip wear phenomenon was detected through adhesion force measurements before and after the test. Even at nanoscales, the wear resistance was found to be directly dependent on the hardness of the phases