Corrosion Current Density Values Research Articles

EFFECT OF BURNISHING ON THE CORROSION PROPERTIES OF Ni-5%Al AND Ni-5%Al-15%Al2O3 COATINGS OBTAINED BY PLASMA SPRAYING

The Ni-5%Al alloy coatings and Ni-5% Al-15%Al2O3 composite coatings were obtained by plasma spraying method. The PN120 gun was used. The coatings onto a shaft made of austenitic stainless steel (X5CrNi 18-10) were sprayed. The coatings were subjected to turning, burnishing. The evaluation of corrosion properties were based on the measurements of corrosion current density and corrosion potential (polarization method), the charge transfer resistance and exponent of constant phase element impedance (electrochemical impedance spectroscopy method). Corrosion tests were performed in replacement seawater (3.5% sodium chloride solution). On the basis of studies, the effect of finishing type on the corrosion properties of plasma sprayed coatings has been demonstrated. The lowest corrosion current density was found for Ni-5% Al coatings after burnishing, icorr value equal to 0.96 A/cm 2 , and the charge transfer resistance was 27007 Ωcm 2 . The lowest resistance to corrosion of turned Ni-5%Al-15%Al2O3 composite coatings was observed. These coatings were characterized by the following parameters of corrosion process: icorr = 17.64 A/cm 2 , Rct = 2137 Ωcm2. Burnishing caused increased corrosion resistance of coatings. Due to reduced roughness and waviness are obtained reduction of the area of the actual burnished coatings compared to turned coatings. Thus, it is resulting in reduced values of corrosion current density. After finishing treatment, the plasma sprayed Ni-5%Al-15%Al2O3 coatings characterized by lower corrosion resistance compared to the alloy coating. The presence of the reinforcing phase in the coating promotes the increase of the porosity. The plasma sprayed coatings on nickel matrix had a tendency to localized corrosion in sodium chloride solution.

Experimental investigation on durability performance of rubberized concrete

The study presented herein aims to investigate the durability related properties of rubberized concrete. Two types of waste scrap tire rubber were used as fine and coarse aggregate, respectively. The rubber was replaced with aggregate by three crumb rubber and tire chips levels of 5, 15, and 25% for the rubberized concrete productions. In order to improve the transport properties and corrosion resistance of rubberized concretes, SF was replaced with cement at 10% replacement level by weight of total binder content. The transport properties of the rubberized concretes were investigated through water absorption, gas permeability, and water permeability tests. The corrosion behavior of reinforcing bars embedded in plain and silica fume based rubberized concretes was investigated by linear polarization resistance (LPR) test. The results indicated that the utilization of SF in the rubberized concrete production enhanced the corrosion behavior and decreased corrosion current density values. Moreover, the reduction in the water and gas permeability coefficients was observed by the incorporation of SF in plain and especially rubberized concretes.

Protective properties of cataphoretic epoxy coating on aluminium alloy AA6060 modified with electrodeposited Ce-based coatings: Effect of post-treatment

Abstract Ce-based conversion coatings (CeCCs) are a promising alternative to toxic chromate coatings on the metal substrates. In this work the CeCCs were electrodeposited on aluminium alloy AA6060 from aqueous solution of Ce(NO3)3 at different potentials (−0.95 V, −1.2 V and −1.4 V). Effect of deposition potential and post-treatment in the phosphate solution on morphology and protective properties of CeCCs with top cataphoretic epoxy coating was studied. To assess the differences between the protective systems, originating from the different CeCCs pre-treatments, electrochemical impedance spectroscopy (EIS), polarization measurements, AFM and SEM/EDS analysis were used. The EIS study was undertaken to follow the evolution of corrosion behaviour of epoxy coating/CeCCs protective systems over prolonged time of exposure to the chloride environment (3 wt.% NaCl). Results suggest significantly improved corrosion stability of epoxy coating on AA6060 with as-deposited CeCCs sub-layers with respect to the same epoxy coatings with phosphate post-treated CeCCs. The far best protective properties, i.e., the greatest value of pore resistance and the lowest value of corrosion current density were provided by the epoxy coating/CeCC protective system with CeCC deposited at −1.2 V and without post-treatment.

Designing a toxic-element-free Ti-based amorphous alloy with remarkable supercooled liquid region for biomedical application

A series of toxic-element-free Ti–Zr–Ta–Si amorphous alloy ribbons have been successfully prepared by melt-spinning. The differential scanning carlorimetry (DSC), X-ray diffraction analysis, bending test and microhardness test are conducted for studying the thermal and mechanical properties. The results show that the Ti42Zr40Ta3Si15 metallic glass ribbon present excellent ductile behavior by the bending testing, without any fracture cracking after bending over 180 degree. In addition, this amorphous alloy possesses a very high glass transition and crystallization temperature of 799 and 898 K, respectively, as well as a very wide supercooled liquid region of 99 K. This amorphous alloy exhibits promising thermal stability during isothermal annealing at the middle temperature of its supercooled region, with more than 3000 s incubation time for isothermal annealing at 823 K (550 °C). This amorphous alloy also shows much lower value of corrosion current density (2.27 × 10−9 A/m2) than the 304 stainless steel in the 0.3 mass% sodium cloride solutions. This Ti42Zr40Ta3Si15 alloy is believed to be a promising based alloy for fabricating the bulk metallic glass foam by the spacer technique in the application of biomedical implants.

Effect of Al/Cu ratios on the optical, electrical, and electrochemical properties of Cu–Al–Ca–O thin films

This study systematically investigated the effect of various Al/Cu ratios on the optical, electrical, and electrochemical properties of sputter-deposited CuAlx−0.2Ca0.2O (x=1, 1.25, 1.5, 1.75, 2) thin films. The as-sputtered Cu–Al–Ca–O films were all amorphous regardless of Al/Cu ratio. Both the transmittance and resistivity of the Cu–Al–Ca–O films increased with increasing Al/Cu ratios. Heterojunction diodes fabricated using Al-doped ZnO, ZnO, and Cu–Al–Ca–O thin films of various Al/Cu ratios exhibited high breakdown-voltage values when Cu–Al–Ca–O thin films with high Al/Cu ratios. Optimal rectification ratio and electrical properties were determined in diodes that had CuAl1.3Ca0.2O as their p-layer deposited film. Cu–Al–Ca–O films with high Al/Cu ratios exhibited low average corrosion current density (icorr) values and high breakdown-voltages (Ebr) values, indicating that the corrosion resistance of Cu–Al–Ca–O film increases with increasing Al/Cu ratios.

Effect of different cooling methods on the corrosion behaviour at welded area of aluminium alloy

The effect of different cooling methods on the corrosion behaviour at welded area of aluminium alloy 5083 was investigated by using weight loss study, potendynamic polarization study and morphology study. All samples were cooled by using air cooling method and quenching method. There was an increase of weight loss for both cooling methods where samples with air cooling method showed lower percentage of weight loss as compared to samples with quenching methods. The corrosion rate gained from this study revealed that samples with air cooling method showed lower corrosion rate compared to samples with quenching method. In potentiodynamic polarization study, the value of corrosion current density, Icorr increased with respect to immersion period. This behaviour signifies the occurrence of porosity where the air cooled samples show lower value of Icorr compared to quenched samples. The increase in Icorr causes the value of polarization resistance, Rp to decrease and corrosion rate to increase. The morphology study conducted revealed the existence of porosity and caused pitting corrosion on quenched samples which proved the samples with quenching method was more corroded as compared to samples with air cooling method.

Effect of solution pH on electrochemical and stress corrosion cracking behaviour of a 7150 Al–Zn–Mg–Cu alloy

Potentidynamic polarization test and slow strain rate test (SSRT) have been carried out on a 7150 alloy of various tempers in 3.5wt% NaCl solution at pH 7, pH 1 and pH 12. The measured corrosion current density (icorr) values determined from the polarization curves are higher in solution pH 1 and pH 12 compared to that in solution pH 7. Slow strain rate test (SSRT) results exhibited that highly over-aged temper has higher resistance to stress corrosion cracking (SCC) compared to that of under aged (T4) and peak aged (T6) tempers. Further, for all the alloy tempers, the SCC susceptibility was the most severe in solution pH 1, intermediate in solution pH 12 and least in solution pH 7. The observed SCC behaviour of the alloy tempers has been explained with the TEM micrographs, SEM fractographs and optical micrographs of crack morphology. Local anodic dissolution (LAD) of grain boundary precipitates exacerbated by stress and accompanied by hydrogen induced cracking (HIC) are the probable mechanisms to induce SCC in the 7150 alloy of T4 and T6 tempers.

Effect of heat treatment on structures and corrosion characteristics of electroless Ni–P–SiC nanocomposite coatings

Ni–P–SiC nanocomposite coatings were successfully deposited onto mild steel substrates. The coating process was performed by sealing the specimens in an evacuated tempered glass tube and heated at various temperatures of 200°C for 2h, 400°C for 1h, and 600°C for 10min. The effect of heat treatment on the structures and corrosion characteristics of the electroless Ni–P–SiC nanocomposite coatings was investigated by atomic force microscopy (AFM), X-ray diffraction (XRD), Vickers hardness, cyclic polarization, and electrochemical impedance spectroscopy (EIS) analyses. AFM and XRD results indicate that the optimum grain diameters of Ni and SiC in the as-plated Ni–P–SiC nanocomposite coatings are approximately 96.8 and 49.1nm, respectively. The maximum microhardness for the as-plated Ni–P–SiC nanocomposite coatings is 968.3HV. The highest microhardness is achieved for the samples heat treated at 600°C for 10min because of the precipitation of NixPy phases and the formation of an inter-diffusional layer at the substrate-coating interface. The lowest corrosion current density value is obtained for the coatings heat treated at 400°C for 1h. EIS data confirm these results.

Linear Polarization Method Research of Quantitative Detection Based on Concrete Reinforcement Corrosion

In order to achieve internal reinforcement of concrete bridges quantitative nondestructive testing, this paper has adopted linear polarization method to test reinforcement passivation in the pore solution of simulated concrete and corrosion current density value in the corrosion process under different external environments and has built calculation model for amount of reinforcement corrosion based on detection signal. That is to say a new idea, which makes the evaluation results more effective, has been put forward to efficiently correspond with reinforcement corrosion ratio with potential signal, and the quantification evaluation for damage of reinforced concrete can be carried directly. It has modified theoretical model and analyzed the error through weightlessness tests. The research result shows that the calculation model after modified can significantly improve the detection accuracy for the actual rate of reinforcement corrosion. CLC: TU528.33 Document code:

Physical deposition of carbon doped titanium nitride film by DC magnetron sputtering for metallic implant coating use

Alloys exposed to tissue environment are at risk to corrosive breakdown. The corrosion behaviour of carbon doped titanium nitride films was studied. The C-TiN films were deposited by DC magnetron sputtering. The obtained films were investigated to be used as protective layers for medical implants. The films were analysed using XRD, SEM with EDX, FTIR, Raman, UV-vis and potentiodynamic polarization. Analysis indicated that doping with carbon in low concentration led to form titanium carbide. The measured values of corrosion current densities (Icorr, substrate=2.020μA/cm2, Icorr, coating=0.175μA/cm2) indicate that the deposited films improved the corrosion resistance of the pure titanium. Comparison between the corrosion current densities of two samples (uncoated and coated pure titanium) showed a reduction of 91% in corrosion current density for coated Ti compared to the uncoated one.

Effect of Grain Size on the Corrosion Resistance of Friction Stir Welded Mg Alloy AZ31B Joints

The objective of this study was to clarify the effect of grain size on the corrosion rate across friction stir welded AZ31B joints when exposed in aqueous NaCl solutions. Grain size variations were achieved by preparing welded joints using AZ31B in different tempers. Single potentiodynamic polarization measurements made on the isolated base metal and stir zone in 0.6 M NaCl solution revealed no significant difference between the anodic kinetics, but revealed an apparent difference between the cathodic kinetics. The attempt to correlate extracted corrosion current density (icorr) values to grain size (d−0.5) revealed that the slope coefficient was insignificantly different from zero, meaning that no meaningful correlation exists (albeit during the corrosion propagation stage). Scanning vibrating electrode technique (SVET) measurements across an intact AZ31B-O welded joint revealed that grain size had a more complex effect on the anodic and cathodic kinetics of the filiform-like corrosion exhibited in 0.86 M NaCl solution. Grain size had an effect on filament initiation as it consistently occurred on the surface of the base alloy (coarser-grained structure). In contrast, grain size had no effect on filament propagation as the anodic and cathodic kinetics were unaffected when moving from the base metal (coarser-grained surface) across the stir zone (finer-grained surface).

Effect of different cooling methods on the corrosion behavior at welded area of aluminium alloy

The effect of different cooling methods on the corrosion behaviour at welded area of aluminium alloy 5083 was investigated by using weight loss study, potendynamic polarization study and morphology study. All samples were cooled by using air cooling method and quenching method. There was an increase of weight loss for both cooling methods where samples with air cooling method showed lower percentage of weight loss as compared to samples with quenching methods. The corrosion rate gained from this study revealed that samples with air cooling method showed lower corrosion rate compared to samples with quenching method. In potentiodynamic polarization study, the value of corrosion current density, Icorr increased with respect to immersion period. This behaviour signifies the occurrence of porosity where the air cooled samples show lower value of Icorr compared to quenched samples. The increase in Icorr causes the value of polarization resistance, Rp to decrease and corrosion rate to increase. The morphology study conducted revealed the existence of porosity and caused pitting corrosion on quenched samples which proved the samples with quenching method was more corroded as compared to samples with air cooling method.

One-step fabrication of oriented Mg/Al-layered double hydroxide film on magnesium substrate with urea hydrolysis and its corrosion resistance

This work presents a simple and direct method for synthesizing Mg/Al-layered double hydroxides (MgAl-LDHs) film on an Mg sheet by in situ hydrothermal crystallization with urea hydrolysis, and protecting the Mg sheet from corrosion. The morphology and structure of the LDHs film were characterized by scanning electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy, respectively. A uniform and compact thin film was formed, of which the LDHs platelets were highly oriented with their ab-face perpendicular to the Mg substrate. XRD pattern and FT-IR spectrum show that MgAl-LDHs film was formed accompanied with Mg(OH)2. Polarization measurements showed that the LDHs film exhibited a low corrosion current density value of 10−6 A/cm2. The strong adhesion between the film and the substrate was observed by cross-cutting method. These results indicated that the LDHs film can effectively protect Mg sheet from corrosion.

Pulse electrodeposition and characterization of nano Ni–W alloy deposits

Pulse plating was employed to obtain Ni–W alloy nanodeposits from ammonical citrate bath. Effects of peak current density, pH, tungstate ion concentration and temperature on the cathodic current efficiency were studied. Ni-32.8 weight (wt)% of W alloy coating was obtained using optimized bath composition. Ni–W solid solution was found in the alloy deposit. Surface morphology studies revealed that the alloy surface was covered by long needle like crystals. XRD patterns of the electrodeposits showed only fcc (nickel) peaks. The hardness of the deposits obeyed Hall–Petch relation. Electrochemical polarization studies revealed that the corrosion potentials of nickel became nobler with W addition and corrosion current density values decreased. Electrochemical impedance studies found that, the increased charge transfer resistances suggesting decreased corrosion current density values. The capacitance values of the double layer decreased with W additions.

Effect of Nano Zirconia on Microstructure and Electrochemical Behavior of Aluminium-Zinc Sacrificial Anodes

In this study, nano ZrO2 powders were incorporated into Al-5 wt% Zn sacrificial anode and the effect of ZrO2 contents (wt% =0.1, 0.2) on microstructures and electrochemical properties were investigated. The results show that the addition of nano ZrO2 was effective on improving metallurgical and electrochemical properties. With the increase of ZrO2 content, the dendritic structure is fined gradually and the corrosion current density values is also increased. The incorporation of ZrO2 also can result in a moderate efficiency value. When the ZrO2 content in the alloy was 0.2 wt%, the optimal microstructure, electrochemical properties and as high as 70% the efficiency value was obtained.

The surface and electrochemical analysis of permanganate based conversion coating on alclad and unclad 2024 alloy

In the present investigation permanganate based conversion coating (PCC) was developed on AA 2024 alloy using alkaline bath containing Mn/Mo oxyanions. Conversion coating was formed on alclad (APCC) and unclad (UPCC) aluminium alloys by simple immersion method. Surface morphology of the APCC and UPCC specimens exhibited smooth and mud-crack patterns respectively. Elemental analysis showed the presence of higher amounts of Mn (5–6wt.%) and Mo (0.3wt.%) on UPCC. Raman and XPS analysis showed the presence of compounds such as MnOx (Mn3O4 and Mn2O3), MnO2, KMnO4, MoOx, MoO2, MoO3/polymolybdate on both coating surfaces. The corrosion current density (icorr) values obtained for both coated surfaces were less than 1μA/cm2. However, APCC specimen showed the lowest icorr value of about 0.05μA/cm2 after 168h of immersion in 3.5% NaCl. EIS studies revealed the higher charge transfer resistance (Rct) values for APCC specimen after 1 and 168h immersion compared to UPCC. Coated specimens were also tested by continuous salt spray exposure (ASTM B117) with and without cross-hatch mark (‘X’) for about 750h. Coating discoloration along with the presence of few corrosion products had been noticed on UPCC specimen after continuous salt spray exposure.

Characterisation of high pressure torsion processed 7150 Al–Zn–Mg–Cu alloy

Solution treated 7150 Al–Zn–Mg–Cu alloy samples were subjected to high pressure torsion (HPT) at room temperature and artificial ageing. Microhardness of HPT processed samples increases with distance from the centre, saturating near the edge of the disk. The hardness obtained through HPT processing is higher compared to that obtained by conventional solution treatment and artificially ageing of this high strength aluminium alloy. Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) revealed the sequence of solid state reactions occurring in the Al–Zn–Mg–Cu system, and the presence of β′ (Al3Zr), η′ (MgZn2) and η (MgZn2) phases, respectively. TEM of HPT processed samples revealed that the grains near the edge of the disk are finer compared to that near the centre of the disk. Electrochemical polarisation studies of the HPT processed 7150 alloy indicated open circuit potential (OCP) and corrosion potential (Ecorr) values are more negative (i.e. anodic), and corrosion current density (icorr) values are about one order higher than the values of artificially aged tempers.

Study of different aluminum alloy substrates coated with Ni–Co–P as metallic bipolar plates for PEM fuel cell applications

Pure Al and some of its alloys [Al alloy 6061 (AA6061), Al alloy 3004 (AA3004) and Al alloy 1050 (AA1050)] were coated with Ni–Co–P using electroplating power supply technique. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques were applied to study the surface morphology and chemical composition of coated aluminum substrates. Their performance against corrosion was examined using potentiodynamic polarization technique in (0.5 M H2SO4 + 2 ppm HF) solution. Corrosion potential values were shifted in the positive direction at all aluminum substrates after their coating with Ni–Co–P. Corrosion current density values at coated pure Al and AA1050 were decreased by ∼18.6 times, compared to those at bare substrates. The stability of coated aluminum alloys was investigated during long-time operation under cathodic environment in PEMFCs using potentiostatic polarization test at +160 mV (MMS) in air-saturated solution. Ni–Co–P/AA3004 substrate showed a high corrosion rate after short time, while coated AA6061 one slowly corroded. Interfacial contact resistance (ICR) values between metallic bipolar plates and gas diffusion layer were measured. Coating AA1050 with Ni–Co–P reduces its ICR value by 13 times. Accordingly, electroplated Ni–Co–P/AA1050 substrate can be chosen as an efficient bipolar plate material in PEMFCs.

STUDY ON Al--BASED AMORPHOUS AND NANOCRYSTALLINE COMPOSITE COATING

An Al-Ni-Y-Co amorphous and nanocrystalline composite coating was prepared on the surface of the AZ91 Mg alloy by using an automatic high velocity arc spraying system.Its microstructures were analyzed by scanning electron microscope(SEM),X-ray diffraction(XRD) and transmission electron microscope(TEM).The results show that the coatings compose of amorphous,nanocrystalline and microcrystalline phases,which has a compact structure with low porosity about 1.8%.The average Vickers microhardness and bond strength of this coating are 311.7 HVo.i and 26.8 MPa.Its relative wear resistance is about 10 times than that of Al coating and 6 times than that of AZ91 magnesium alloy.The corrosion potential of this coating is more positive than that of Al coating and AZ91 magnesium alloy,and the corresponding corrosion current density value is about 1/2 the same as that of Al coating and 1/5 as that of AZ91 Mg alloy.Especially,compared with the surface on corroded Al coating and AZ91 Mg alloy,the corroded Al-Ni-Y-Co coating has a more flattered surface with less corrosive piting than Al coating.It is confirmed that the Al-Ni-Y-Co coating is an excellent coatinig with higher wear-resistance and corrosion resistance.

Effect of heat treatment on the properties of electroless Ni–P–carbon nanotube composite coatings

Electroless Ni–P–carbon nanotube composite coatings were deposited on API-5L X65 steel substrates. The coatings were vacuum heat treated at temperatures of 200°C for 2 h, 400°C for 1 h and 600°C for 15 min. Microhardness measurement, X-ray diffraction (XRD) technique, scanning electron microscopy, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) were used to study the effect of heat treatment on the properties of the coatings. XRD results indicated that the as-plated coating had either nanocrystalline or a mixture of amorphous and nanocrystalline structure. Heat treatment of the coatings above 400°C produced a mixture of polycrystalline phases. The highest microhardness was achieved for the samples heat treated at 600°C for 15 min because of the precipitation of NixPy phases and formation of an inter-diffusional layer at the substrate/coating interface. The lowest corrosion current density value was obtained for the coatings heat treated at 400°C for 1 h. EIS experiments confirmed the results.