Electrochemical properties of microarc oxidation films on a magnesium alloy modified by high-intensity pulsed ion beam

Microarc oxidation (MAO) films on AZ31 magnesium alloy were treated by high-intensity pulsed ion beam (HIPIB) irradiation with ion energy of 300 keV at ion current density of 200 A/cm². A remelted layer of a few micrometers was produced on irradiated MAO films. The corrosion resistance of MAO films was characterized by potentiodynamic electrochemical test in 3.5% NaCl solution. The anodic polarization behavior of MAO samples exhibited a transition from the active anodic dissolution for the original one to the passivation-pitting breakdown for the modified films. The passivation-pitting breakdown voltage of modified films increased with multi-shot irradiation, i.e. from a value of − 1420 mV(SCE) at 1 shot to − 800 mV(SCE) at 5 shots, and the corresponding passivation current density decreased by two orders of magnitude. The irradiated MAO films have a higher corrosion potential than the original one, reaching a maximal value of − 1350 mV(SCE) at 5 shots from the original − 1580 mV(SCE). The electrochemical impedance spectrum (EIS) of modified MAO films was measured with varying the immersion time in 3.5% NaCl solution. The Nyquist impedance plots from modified films may show only a capacitive loop at the immersion time of 5 h, and the inductive loop occur at longer immersion time, whereas original films presenting both capacitive and inductive loops at all the immersion time. Bode plots of MAO films before and after irradiation were obviously distinguished in shape at low frequency range, especially at short immersion time. The evolution of Nyquist and Bode plots with immersion time was discussed in association with the processes of electrolyte penetration into the MAO structure and resultant reaction at the film-substrate interface. It is concluded that the improvement in the continuity and compaction of MAO films accounts for the enhanced corrosion resistance of the films irradiated by HIPIB.     

Composition and structure of Al ions implanted Fe at elevated temperatures

Al ions with ion energy of 120 keV are implanted into Fe under ion current density of 3.18 μA/cm² to implantation doses of 5 × 10¹⁶ and 1 × 10¹⁷ ions/cm² at room temperature and elevated temperatures of 250 and 500 °C, respectively. At 250 °C, the distribution depth of implanted Al reaches 160 nm with a peak concentration of 6 at.% at the dose of 5 × 10¹⁶ ions/cm², and 180 nm with 10 at.% at 1 × 10¹⁷ ions/cm², analyzed by Rutherford backscattering spectroscopy, respectively. At 500 °C, the implantation depth is 200 nm and the maximum concentration of Al is 10 at.% at the dose of 1 × 10¹⁷ ions/cm². With 5 × 10¹⁶ ions/cm², the intermetallics Al₁₃Fe₄ is formed in the Fe samples at 500 °C, revealed by X-ray diffraction. With 1 × 10¹⁷ ions/cm², the phase is also detected at 250 °C. The concentration-depth profiles of implanted Al in Fe samples at the room temperature, 250 °C and 500 °C are calculated by a mass transfer model that is built based on the transport of ions in matter and the irradiation enhanced diffusion. The calculated concentration-depth profiles are in reasonable agreement with those obtained from the experiments.     

Improving wear resistance and corrosion resistance of AZ31 magnesium alloy by DLC/AlN/Al coating

A novel protective coating, consisting of three layers (top: diamond-like carbon, middle: aluminum nitride, bottom: aluminum), was deposited on the surface of AZ31 magnesium alloy layer by layer. Nano-indenter, electrochemical system and tribological tester were performed to investigate the hardness, wear resistance and corrosion resistance of the coated AZ31 magnesium alloy, respectively. The DLC/AlN/Al coating improved the magnesium alloy's surface hardness and reduced its friction coefficient, which consequently induced a great improvement of the magnesium alloy's wear resistance. Furthermore, the corrosion resistance of the AZ31 magnesium alloy with the DLC/AlN/Al coating was also enhanced with the corrosion current density decreasing from 2.25 × 10⁻⁵ A/cm² to 1.28 × 10⁻⁶ A/cm² in a 3.5 wt.% NaCl solution.     

Influence of N ion implantation on the corrosion and nano-structure of Ti samples

Nitrogen ions of 30 keV with different fluxes ranging from 5 × 10¹⁶ to 8 × 10¹⁷ ions/cm² were implanted in Ti foil of 1.8 mm thickness. X-ray diffraction (XRD) was used to obtain the structural characteristics, while atomic force microscope (AFM) was employed to obtain the surface morphology of the samples. The potentiodynamic method was employed to obtain corrosion resistance of the samples in NaCl (3.5%) solution. Titanium nitride formation was enhanced with increasing the nitrogen ion flux, while grain size and surface roughness of the samples were also increased. Optimum corrosion resistance was obtained for 5 × 10¹⁶ (N⁺ ions/cm²).     

Electrochemical studies of stainless steel implanted with nitrogen and oxygen by plasma immersion ion implantation

Plasma Immersion Ion Implantation (PIII) of stainless steel with nitrogen at temperatures lower than 400 °C has been reported to increase the hardness of the material by several times. However, expectations that the corrosion resistance will remain unaffected after implantation were not found to be so. In the present study the influence of post-oxygen implantation on the corrosion resistance of nitrogen implanted stainless steel is presented. Stainless steel samples were subjected to oxygen, nitrogen and post-oxygen ion implantation at different temperatures. GIXRD and microRaman studies of the implanted samples showed that oxygen implantation leads to the formation of an oxide layer consisting of corundum and spinel structures. The corrosion properties of the implanted samples were studied by potentiodynamic polarization and electrochemical impedance techniques in 3.5% NaCl solution. After nitrogen implantation the corrosion current increased and the corrosion potential shifted to the less noble side to − 0.486 V as compared to − 0.284 V for the substrate. Oxygen implantation at 400 °C shifted the corrosion potential to the nobler side to − 0.2 V with decrease of corrosion current. For post-oxygen ion implantation at temperatures lower than 400 °C, the corrosion current was higher than the substrate and the corrosion potential was also on the less noble side. However, post-oxygen ion implantation at 400 °C after nitrogen ion implantation resulted in improved corrosion resistance as the corrosion potential shifted to nobler side and the corrosion current was lower than that of substrate.     

Properties of the TiN coatings on previously Ti ion-implanted magnesium alloy substrate

To enhance the mechanical properties of TiN coating on magnesium alloy, metal vapor vacuum arc (MEVVA) ion implantation was performed to modify magnesium alloy substrate before TiN film deposition. Implantation energy was fixed at 45 keV and dose was at 9 × 10¹⁷ cm^− 2. TiN coatings were deposited by magnetically filtered vacuum-arc plasma source on unimplanted and implanted substrate. The microstructure composition distribution and phase structure were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The chemical states of some typical elements of the TiN coating were analyzed by means of X-ray photoelectron spectroscopy (XPS). The properties of corrosion resistance of TiN coatings were studied by CS300P electrochemical-corrosion workstation, and the mechanism of the corrosion resistance was also discussed.     

Electrochemical behaviour of chromium-implanted magnesium in hydroxide, chloride and sulphate solutions

Despite the development and subsequent improvement of new Mg-based alloys, their vulnerability to oxidation and corrosion continues to pose a major obstacle to their more generalized use. The possibility of blocking high diffusivity paths, such as grain boundaries, by ion implantation may help to improve their oxidation and corrosion resistance, because mass transport through these short circuiting paths is reduced.Electrochemical techniques were used to investigate the effect of Cr ion implantation in the electrochemical behaviour of Mg in aqueous solutions. In particular ion implanted fluences of 5 × 10¹⁶ and 5 × 10¹⁷ at./cm² have been evaluated in solutions of NaCl, NaOH and Na₂SO₄.The corroded surfaces and products were analysed by ion beam analysis, scanning electron microscopy and X-ray diffraction. A model of the corrosion mechanism is proposed to explain the obtained results.     

X-ray photoelectron spectroscopy study of the corrosion behaviour of galvanised steel implanted with rare earths

The present paper studies the effect of ion implantation of 2 × 10¹⁶ ions/cm² of Ce⁺ and 2 × 10¹⁶ ions/cm² of La⁺ at 150 keV on the corrosion behaviour of hot-dip galvanised steel. After implantation, galvanised steel was characterised by means of XPS previous to and following immersion in the medium. The results revealed incorporation of cerium and lanthanum on the surface as Ce₂O₃ and La₂O₃, respectively. Electrochemical impedance spectroscopy was carried out in order to evaluate its corrosion behaviour in 0.6 M NaCl during 1 month of immersion. The corrosion resistance was improved by an increase in the charge transfer resistance of the implanted specimens in the medium. This effect could be associated with changes in the morphology/microstructure of the corrosion products layer rather than in its composition variations.     

Optical properties of antimony-implanted ZnO epilayers

Antimony ions were implanted into ZnO films grown on c-plane sapphire by pulsed-laser deposition. Raman scattering modes of the Sb-implanted samples were found to be influenced by the implantation dose. A characteristic peak at 576 cm^− 1 was observed with an asymmetric shape due to ion damage to the lattice of the implanted ZnO films. When the implant dose was low, the height of the peak was reduced by rapid thermal annealing at 400-600 °C and the symmetry of the spectra was recovered. However, when the Sb dose exceeded 1 × 10¹⁵ cm^− 2, the peak maintained unchanged after rapid thermal annealing at temperatures up to 600 °C. A broad and low Raman peak was observed at 437 cm^− 1, which is related to the surface damage caused by the energetic ion bombarding. Photoluminescence measurement showed a decrease of the bandedge emission at 3.36 eV, a clear effect of defects induced by the implantation, and confirmed partial recovery of the crystal by rapid annealing.     

Parametric study of nitrided AISI 304 austenite stainless steel prepared by plasma immersion ion implantation

This paper investigates the characteristics of plasma immersion nitrogen-ion implanted AISI 304 austenite stainless steel against such processing parameters as bias voltage (5-20 kV), substrate temperature (300-500 °C), and implantation fluence (1.4 × 10¹⁸-4.2 × 10¹⁸ cm^− 2). Characteristics of the as-implanted specimens under investigation included elemental depth profile, hardness depth profile, crystallographic structure, and corrosion behavior and were determined using glow discharge spectrometry (GDS), the Vickers hardness tester, X-ray diffractometry (XRD), and the potentiodynamic polarization test, respectively. The results show that nitrogen depth profiles strongly depend on these processing parameters and closely relate to the corresponding chromium depth profiles. The hardness depth profiles increase and widen as substrate temperature, bias voltage, and implantation fluence increase. In particular, an improvement in hardness is accompanied by a reduction in corrosion resistance when substrate temperature reaches 500 °C. The corrosion-resistance degrader, CrN, precipitates as substrate temperature exceeds 450 °C, a phenomenon which is clearly evident in the chromium depth profiles as well as the XRD results.     

Corrosion behaviour of nitrogen ion implanted AISI type 304L stainless steel in nitric acid medium

The effects of nitrogen ion implantation on corrosion behaviour of 304L stainless steel in 1 N HNO₃ medium were investigated using surface analytical and electrochemical techniques. Nitrogen ion was implanted at 70 keV in the dose range of 1 × 10¹⁵, 1 × 10¹⁶, 1 × 10¹⁷ and 2.5 × 10¹⁷ N⁺/cm², respectively. Grazing incidence X-ray diffraction results for unimplanted and up to dose of 1 × 10¹⁶ N⁺/cm² showed co-existence of γ-Fe and α′-Fe and, at higher doses (1 × 10¹⁷ and 2.5 × 10¹⁷) preferential formation of chromium nitride was observed. X-ray photoelectron spectroscopy investigation confirmed the formation of chromium nitride at higher doses. Electrochemical corrosion investigation revealed nobler open circuit potential, decrease in corrosion current densities, passive current densities and increase in polarization resistance with increase in dose rate. Surface morphology analysis after polarization study using atomic force microscope showed grain boundary dissolution for unimplanted specimens and resistance to surface dissolution with increase in dose rate for implanted specimens.     

Surface characterization of passive film formed on nitrogen ion implanted Ti-6Al-4V and Ti-6Al-7Nb alloys using SIMS

The aim of this paper is to study the effect of N⁺ ion implantation on corrosion and phase formation on the implanted surfaces of Ti-6Al-4V and Ti-6Al-7Nb alloys. Nitrogen ion was implanted on Ti-6Al-4V and Ti-6Al-7Nb alloys at an energy of 70 and 100 keV, respectively using a 150 keV accelerator at different doses ranging from 5 × 10¹⁵ to 2.5 × 10¹⁷ ions/cm². Electrochemical studies have been carried out in Ringer’s solution in order to determine the optimum dose that can give good corrosion resistance in a simulated body fluid condition. The implanted surfaces of such modified doses were electrochemically passivated at 1.0 V for an hour. Secondary ion mass spectroscopy was used to study and characterize titanium oxide and titanium nitride layers produced on implanted surface and to correlate them with the corrosion resistance. The nature of the passive film of the implanted-passivated specimen was compared with the unimplanted-passivated as well as as-implanted specimens.     

Corrosion resistance of TiO2 films grown on stainless steel by atomic layer deposition

Titanium dioxide (TiO₂) films have been deposited onto stainless steel substrates using atomic layer deposition (ALD) technique. Composition analysis shows that the films shield the substrates entirely. The TiO₂ films are amorphous in structure as characterized by X-ray diffraction. The electrochemical measurements show that the equilibrium corrosion potential positively shifts from − 0.96 eV for bare stainless steel to − 0.63 eV for TiO₂ coated stainless steel, and the corrosion current density decreases from 7.0 × 10^− 7 A/cm² to 6.3 × 10^− 8 A/cm². The corrosion resistance obtained by fitting the impedance spectra also reveals that the TiO₂ films provide good protection for stainless steel against corrosion in sodium chloride solution. The above results indicate that TiO₂ films deposited by ALD are effective in protecting stainless steel from corrosion.     

Influence of fluoride ion on the electrochemical behaviour of β-Ti alloy for dental implant application

The corrosion behaviour of Ti-15Mo alloy in 0.15 M NaCl containing 0.01, 0.03, 0.06 and 0.5 M NaF is evaluated and its protective ability is compared with that of CP-Ti and Ti-6Al-4V alloy, to ascertain their suitability for dental implant application. The steady state current density of CP-Ti and, Ti-15Mo and Ti-6Al-4V alloys in 0.15 M NaCl containing 0.03 M NaF at 200 mV vs. SCE is found to be 1, 2 and 6 μA/cm², respectively, which indicate that all of them could offer a better corrosion resistance in the potential range that could exists in the oral environment.     

Evaluation of metastable pitting on titanium by charge integration of current transients

The metastable pitting of titanium has been studied under potentiostatic control in solutions containing chloride ions. An approach based on the charge integration of current transients was proposed for a quantitative determination of metastable pitting. A pit density (d_mpit) was defined as the number of metastable pits per unit area per unit time (cm⁻² h⁻¹) with a typical size, instead of a size distribution. The calculated d_mpit of titanium at 0.5 V_SCE in 0.6 M NaCl was about 1.0 × 10³ cm⁻² h⁻¹ with a typical radius of 0.12 μm. An exponential potential dependence of d_mpit was obtained through the integration approach.     

The beneficial role of Y-implantation on the aqueous corrosion of stainless steel

The corrosion behaviour of Y-implanted austenitic stainless steel AISI 321 samples was investigated in 0.5 M H₂SO₄ at ambient temperature using potentiodynamic polarization and cyclic voltammetry. The implantation of 1 × 10¹⁶ Y-ions/cm² of 40 keV energy did not lead to an improvement of the corrosion resistance of the material because of sputtering effects. On the other hand, a significant improvement of the corrosion resistance was observed by increasing of the dose (2 × 10¹⁷ Y-ions/cm² implanted in the presence of oxygen) and the implantation energy (55 and 80 keV). The elemental composition of the near-surface layers of the implanted steel samples prior and after the corrosion attack was determined by Rutherford backscattering spectrometry (RBS) and Nuclear Reaction Analysis (NRA) using alpha particles, protons and deuterons as projectiles. The surface morphology and microstructure of the non-corroded and corroded samples were examined by Scanning Electron Microscopy (SEM). The corrosion resistance of the implanted materials was found to be related with the thickness and the composition of the implanted layer.     

Corrosion behavior of Cu–Al–Be shape memory alloys with different compositions and microstructures

The corrosion behavior of Cu–Al–Be shape memory alloys with different microstructures and Be content in a 3.5% NaCl solution was studied by weight loss, cyclic anodic polarization and chronoamperometric measurements. The beryllium has a beneficial effect in β alloys. A pitting potential of −100 mV/SCE was found by anodic polarization tests for all the studied alloys, corresponding to the formation of pits produced by severe dealuminization. Samples with precipitates were more susceptible to pit formation. The corrosion behavior is strongly affected by the alloy microstructural conditions, and the β samples present higher pitting resistance and repassivation ability.     

Determination of electrochemical parameters and corrosion rate for carbon steel in un-buffered sodium chloride solutions using a superposition model

Corrosion of carbon steel in un-buffered NaCl solutions was studied applying linear potential sweep technique to a rotating disk electrode. Current-potential curves were obtained from linear potential sweep at a rate of 1 mV s⁻¹ in solution with concentrations in the range 0.02-1 M NaCl and rotation rates in the range 170-370 rad s⁻¹, at 22 °C. Potential sweeps, which were conducted in the potential range −700 to −100 mV/SHE, were started from the cathodic limit in order to approach the measurement of corrosion under rust-free conditions. Polarization curves were analyzed with a superimposition model developed ad hoc and implemented in a computer program, which enabled determining the corrosion rate and kinetics parameters of the underlying anodic and cathodic sub-processes. The anodic sub-process, dissolution of iron, was well described in terms of a pure charge transfer controlled reaction, while the cathodic sub-process, oxygen reduction on iron, was well described in terms of mixed mass transfer and charge transfer control. Increase of electrode rotation rate increases the limiting current of oxygen reduction, which results in an enhanced corrosion rate of carbon steel. Increase of NaCl concentration has a dual effect: the limiting current of oxygen reduction decreases as a result of the influence of NaCl concentration on solution viscosity and the anodic dissolution of iron increases due to the influence of NaCl on pitting formation. However, this last mechanism predominates and a net increase in carbon steel corrosion rate is observed in this case.     

The corrosion of Fe3Al alloy in liquid zinc

A systematic study of the isothermal corrosion testing and microscopic examination of Fe₃Al alloy in liquid zinc containing small amounts of aluminum (less than 0.2 wt.%) at 450 °C was carried out in this work. The results showed the corrosion of Fe₃Al alloy in molten zinc was controlled by the dissolution mechanism. The alloy exhibited a regular corrosion layer, constituted of small metallic particles (diameter: 2-5 μm) separated by channels filled with liquid zinc, which represented a porosity of about 29%. The XRD result of the corrosion layer formed at the interface confirmed the presence of Zn and FeZn_6.67. The corrosion rate of Fe₃Al alloy in molten zinc was calculated to be approximately 1.5 × 10⁻⁷ g cm⁻² s⁻¹. Three steps could occur in the whole process: the superficial dissolution of metallic Cr in the corrosion layer, the new phase formation of FeZn_6.67 and the diffusion of the dissolved species in the channels of the corrosion layer.     

Corrosion behaviour of aluminium in copper containing environment

Corrosion behaviour of pure aluminium galvanically connected to metallic copper or in the presence of Cu²⁺ ions was investigated by electrochemical measurements in Na₂SO₄ and Na₂SO₄ + NaCl test solutions. It has been found that in aerated Cl⁻ ion containing solutions pitting corrosion of aluminium emerged immediately, while in the absence of oxygen this process was less violent. Effect of passivating pre-treatment of aluminium surface on corrosion behaviour Cu-Al bimetallic system is also demonstrated.