•FeCrCuTiV HEA prepared by vacuum arc melting and LMD both form FCC+BCC soild solution structure.•Grain size and Cu-rich (FCC) phase volume fraction of HEA prepared by LMD is smaller.•HEA prepared by ...LMD shows better corrosion resistance due to the reduction of Cu-rich segregation phase.
The microstructure and corrosion resistance of FeCrCuTiV high entropy alloy prepared by vacuum arc melting and laser melting deposition were studied. The microstructure and phase composition of FeCrCuTiV high entropy alloy were characterized by SEM, XRD, EBSD, etc. It is found that both of them are composed of the FCC Cu-rich phase, BCC Fe-rich phase and, BCC V-rich phase. Comparing with FeCrCuTiV high entropy alloy prepared by vacuum arc melting, the grain size of FeCrCuTiV high entropy alloy prepared by the laser melting deposition reduces from 29.48 µm to 1.85 µm. Meanwhile, the Cu-rich phase volume fraction decreases from 44.7 % to 31.5 %. Two reasons contribute to this phenomenon: On the one hand, the higher cooling rate of high entropy alloy makes the grain growth limited and the grain size reduced. On the other hand, the higher cooling rate reduces the volume fraction of intergranular segregation Cu-rich phase formed under non-uniform solidification due to the lack of long-range migration of Cu element, which makes the solidification state of FeCrCuTiV high entropy alloy prepared by laser melting deposition deviate from the ideal thermodynamic equilibrium. In addition, the corrosion resistance test of FeCrCuTiV high entropy alloy prepared by two processes indicates: FeCrCuTiV high entropy alloy prepared by laser melting deposition shows better corrosion resistance under the electrochemical corrosion of salt solution. This result is caused by the reduction of the Cu-rich phase, which weakens its corrosion effect as the anode of galvanic cell. Laser melting deposition technology provides new ideas and methods for controlling the phase structure of complex solid solution high entropy alloys to improve their physical properties.
Nano-TiC powders were doped to increase the corrosion resistance of hot-deformed NdFeB magnets. Effects of the dopant content on their electrochemical corrosion behavior in sulphuric acid solutions ...were studied by various measurement techniques including potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron microscopy and X-ray photoelectron spectrometer. Results showed that low additions of nano-TiC especially at the optimum content of 0.5 wt% can obviously increase the resistances and reduce the corrosion current density. It is ascribed to the dopant hindrance effects on the dissolution of Nd-rich phases and the coverage increase of intermediate products on NdFeB substrate induced by nano-TiC that acted as the favorable sites for adsorption reactions. Maximum increase in inductive resistance and the corresponding reduction in current density were found to be 60.6% and 36.1%, respectively. In addition, the effect mechanism of nano-TiC on corrosion behaviors was discussed based on experimental results.
•Low additions of nano-TiC can increase corrosion resistance of NdFeB in sulphuric acid solutions.•Nano-TiC hinders Nd-rich phase dissolution and increases intermediates coverage on NdFeB substrate.•Effect mechanism of nano-TiC on corrosion behaviors of NdFeB was clarified.
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•The cathodic oxygen reduction reaction of NAB alloys is under kinetic control.•The anodic copper dissolution reaction is under mixed transport-kinetic control.•The cathodic standard ...rate constant decreases with Ni content.•The corrosion resistance under flowing condition is improved via Ni addition.•The improved corrosion resistance is analysed based on the microstructures.
The open circuit potential, cathodic and anodic polarisation characteristics of nickel-aluminium bronze (NAB) with different nickel contents in 3.5 wt.% NaCl solution were investigated under well-defined hydrodynamic conditions. The results showed that irreversible cathodic oxygen reduction reaction was under kinetic control, whereas the reversible anodic copper dissolution reaction was under mixed transport-kinetic control. The increase in Ni content decreased the total amounts of α phase and β' phase in the microstructures of NAB alloys, resulting in the decrease in both cathodic kinetic current and anodic current, and thus improved the corrosion resistance of NAB alloys under flowing conditions.
Biodegradable implants can be used in order to avoid removal surgery. Mg-Zn alloys are considered interesting alternatives for biomedical applications, however, studies concerning the effects of ...microstructural features in the as-solidified condition and segregation aspects on the resulting electrochemical behavior are scarce. This investigation is focused on the evaluation of the electrochemical corrosion of an as-solidified Mg-25 wt.% Zn alloy in a 0.15 M NaCl solution at 25 °C. EIS plots, potentiodynamic polarization curves and equivalent circuits are used. It is shown that Zn segregation affects both the galvanic couple and the cathode-to-anode area ratio. It was found that finer and homogeneously distributed Mg-rich six-fold branched equiaxed dendritic grains induce lower corrosion current density and higher polarization resistance when compared with equivalent results of coarser ones.
•Zn segregation affects the galvanic couple formed by the Mg-rich/eutectic phases.•Finer dendritic grains shown lower corrosion current density and higher polarization resistance.•Coarser microstructure induces to osseointegration in implantation due to microcavities.
•Magnesium (Mg)-based nanocomposites was developed using a novel route.•Hydroxyapatite (HA) nanoparticles was used as the reinforcement.•We investigated the effect of HA nanoparticles shape on the ...Mg’s biodegradation.
This work was carried out to investigate the effect of HA nanoparticle shape on the biodegradation behaviour of a magnesium-hydroxyapatite (Mg-2Zn-0.2Mn-0.5Ca/1HA, wt%) nanocomposite fabricated by a novel route which combines high shear solidification (HSS) and equal channel angular extrusion (ECAE) techniques. Two common shapes of HA nanoparticles, i.e. spherical and needle-like were selected with an average equivalent diameter of 40 nm. The biodegradation rate of the nanocomposite in HBSS Hanks’ Balanced Salt Solution was assessed using electrochemical corrosion and immersion test. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to characterize the surface microstructure, biodegradation morphology and biodegradation products. Experimental results showed that Mg/HA composite with spherical HA nanoparticles exhibited a significantly smaller biodegradation rate of 0.6 ± 0.05 mm/year, compared to 9.41 ± 2.53 mm/year for the nanocomposite with needle HA nanoparticles.
A nanocrystalline TiZrN graded coating was deposited on biomedical titanium alloy by DC reactive magnetron sputtering process. The microstructure and compositions of the coating were characterized by ...XRD, TEM and EPMA. The electrochemical corrosion and bio-tribocorrosion behavior of the coated titanium alloy under open circuit potential (OCP) and applied potentials (−0.15 V ~ +0.25 V) were investigated in Hank's solution with and without 25% calf serum. Compared with TiN coating, the hardness of TiZrN coating is greatly increased due to the Zr solid solution strengthening and nanocrystalline strengthening. Under the conditions of OCP and applied anodic potentials, the TiZrN coated Ti alloy exhibits significantly improved anti-tribocorrosion and anti-friction performances, which are attributed to that the stable Ti and Zr oxide or oxynitride passive film on coating near surface and the increased mechanical properties of the coating decrease the synergistic effect of corrosion and wear. 25% calf serum in Hank's solution enhances the chemical stability of the TiZrN coating through adsorption and bio-lubrication mechanism, and therefore further improves the tribocorrosion performance of the coated Ti alloy.
•Nanograin TiN and TiZrN coating are deposited on Ti alloy by PVD method.•TiZrN coating has better anti-tribocorrosion performance than TiN coating.•Synergistic effect of corrosion and wear promotes the damage of TiZrN coating.•Calf serum improves friction and wear performances of the coated Ti alloy.
Long-term stability in contact with water of organosilane layers formed by octadecyltrimethoxysilane (ODTMS) on polished aluminum alloy (AA2024) through dip-coating was studied by combining SEM, ...water contact angle measurements, and X-ray photoelectron spectroscopy. Similar organosilane layers were formed on AA2024 coated with permanganate conversion coating, 1,2-bis(triethoxysilyl)ethane (BTSE) and hydrated SiO
as under-layers, after which their long-term durability was also tested. During immersion in water for about one month, all the samples exhibited a decrease in hydrophobicity, implying the prepared organosilane layer was not stable over time, gradually hydrolyzing and letting water interact with the underlying layer. In parallel, SEM images of one-layer samples taken after immersion showed clear signs of local electrochemical corrosion, while XPS analysis confirmed a loss of silicon from the surface layer. The highest stability over time was demonstrated by a one-layer sample prepared in an ethanol/water bath for 5 min and by a similar ODTMS layer prepared on hydrated MnO
as an under-layer.
Applied mechanical stress could accelerate the chemical or electrochemical process of metal corrosion in weak acid solution. Series of experimental tests were conducted in this research. The results ...show that there is no obvious correlation between OCP (open circuit potential) values and applied stresses. However, The LPR (linear polarization resistance)corrosion rate increased intensively under the applied stress of 400 MPa. Correspondingly, the EIS (electrochemical impedance spectroscopy) Nyquist diagrams show that all of the plots contain a semicircle over the whole frequency range and the semicircle size decreased with increasing applied stress. The real-time corrosion current square waves triggered by the mechanical stress were successfully monitored by using the potentiostatic method in CO2 saturated brine under 200 mv (above OCP), flow and lower pH condition. This result is significant for many research fields, such as petrochemistry, aerospace and nuclear industries, which suffer weak acid corrosive environment.
In this work, the effects of Hg and Ga additions on the microstructure and electrochemical properties of as-rolled Mg-Hg-Ga alloys are investigated. It can be concluded that the Mg-Hg-Ga alloys are ...composed of α-Mg and Mg5Ga2 phases. The addition of the Hg element not only facilitates the precipitation of Mg5Ga2 phases, but also facilitates the distribution of the Ga element in second phases. During rolling, the main soft mechanism in the Mg-1.5Hg-1.5Ga alloy is dynamic recovery, while that of the Mg-1.5Hg-2.0Ga alloy is dynamic recrystallization. The electrochemical tests reveal that the Mg-1.5Hg-2.0Ga alloy has the best corrosion resistance with the smallest corrosion current density of 0.057 mA cm−2. The Mg-2.0Hg-2.0Ga alloy is discovered to exhibit the most negative discharge potential of − 1.976 V and − 1.967 V (vs. SCE) at current densities of 80 mA cm−2 and 180 mA cm−2, respectively. It can be attributed to the fact that the increasing Hg content greatly increases the proportion of deformed grains as well as the volume fraction of Mg5Ga2 phases in the grains, improving the discharge activity of the Mg-2.0Hg-2.0Ga alloy. It also refines the grains of the alloy and forms many anodic dissolution areas, further promoting the discharge activity of the Mg-2.0Hg-2.0Ga alloy.
•The Hg addition facilitates the precipitation of the Mg5Ga2 phase.•The high proportion of deformed grains deteriorate the corrosion resistance of the Mg-Hg-Ga alloys.•The Mg-2.0%Hg-2.0%Ga alloy has the best discharge performance than the other three alloys.
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•A novel gold metallosurfactant (AuCTAB) has been dip coated over galvanised steel(GS).•SEM and XPS have been used to check the surface composition.•Water Contact Angle confirmed the ...hydrophobic character of the AuCTAB film.•Anti biofouling and anti corrosive ability of the coating has been assessed.•AuCTAB film minimised the halophilic bacterial adhesion to GS.
In order to grow a novel kind of antibacterial Au containing bioactive film with good bio corrosion resistance capability for galvanised steel (GS) we targeted a greener approach towards the synthesis of novel bishexadecyltrimethylammoniumaurate(III)bromide metallosurfactant and assessed its inhibitive action towards biofilm formation and corrosion in artificial sea water salts broth. The synthesized complex was characterised by spectroscopic tools like FTIR (near and far regions), and 1H NMR. Also, the thermo gravimetric measurements and elemental analysis were done to find out the metal content in the metallosurfactant. The successful fabrication of coatings and the changes in the surface chemistry of the substrate made by these coatings during biofilm formation was monitored by X-Ray Photoelectron Spectroscopy (XPS). Further, the hydrophobic nature of the coating was checked by the static water contact angle measurement. The antibacterial efficacy of the fabricated coating against Halobacterium salinarium and Halococcus morrhuae was assessed by Confocal Laser Scanning Microscopy (CLSM) and Scanning Electron Microscopy (SEM). The Electrochemical Impedance Spectroscopy data and Tafel plots marked the coating as an efficient electrochemical corrosion inhibitor. The inhibition efficiency of coatings increases with the increase in the concentration of metallosurfactant solution because of the rise in the hydrophobicity due to the formation of metallomicelles and antibacterial activity of AuCTAB with which higher surface coverage of the films was formed (at higher concentration).
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