Potentiodynamic Polarization Corrosion Tests Research Articles

A new approach to combating corrosion of metallic materials

In this study a new approach that is based on creating surface patterns on metallic surfaces has been used to decrease corrosion in nickel. Patterns of holes with specific diameters (D) and inter-hole spacings (L) were created by laser ablation on nickel and potentiodynamic polarization corrosion tests were carried out in a 0.5M H2SO4 solution. The corrosion potential, ECorr, and current density (ICorr) were determined and compared for different ratios of (D/L). Energy dispersive spectroscopy (EDS) was performed on the surface of the samples to investigate the chemical composition, specifically the oxygen content of different regions of the patterned area before and after corrosion testing. By creating such patterns we are able to produce a surface with heterogeneous wetting properties, to decrease the surface energy and to decrease the contact area between the liquid and the substrate. As a result of the surface patterning a significant improvement of corrosion properties of nickel surface has been achieved. Patterned surfaces showed better corrosion resistance compared to the polished reference samples. In addition, it has been shown that for a few specific patterns the corrosion resistance can be increased by orders of magnitude.

Deposition and properties of zirconia coatings on a zirconium alloy produced by pulsed DC plasma electrolytic oxidation

In this study, zirconium oxide coatings were produced on Zr–2.5wt.% Nb alloy by a plasma electrolytic oxidation (PEO) process using a pulsed DC power source with various frequencies 1000, 2000 and 4000Hz. When a relatively low termination voltage (i.e. 400V) was set, the thickness of the coatings was in a range of 7–15μm and the treatment time to reach the preset voltage was less than 5min. The coatings' phase structure, tribological and corrosion properties were characterized by X-ray diffraction (XRD), pin-on-plate sliding wear test and potentiodynamic polarization corrosion test, respectively. The results indicate that the thickest coating of 15μm can be obtained by adopting the highest frequency pulsed DC, i.e., 4000Hz and the coating has almost the same surface roughness as other two coatings. In spite of the difference in thickness, all the coatings showed a similar phase structure with the main phase of monoclinic ZrO2 and less tetragonal ZrO2 phase. Furthermore, all the PEO coated samples can improve wear and corrosion protection of the Zr alloy, among which the coating produced by the highest frequency (4000Hz) achieved the highest corrosion polarization resistance, wear resistance and lowest friction coefficient under the testing conditions in this study.

The role of Cu-based intermetallics on the pitting corrosion behavior of Sn–Cu, Ti–Cu and Al–Cu alloys

The aim of this study is to evaluate the effect of three different intermetallics; Cu6Sn5, Ti2Cu and Al2Cu, on pitting corrosion of Sn–2.8wt.% Cu, Ti–5wt.% Cu and Al–5wt.% Cu as-cast alloys, respectively. Chill-cast and centrifuged-cast samples were subjected to potentiodynamic polarization corrosion tests in a sodium chloride solution at 25°C. It was found that the intermetallic particles play an important role in the process of pitting corrosion. The results have shown that the pitting potentials (EPit) of all three alloys experimentally examined have been displaced about 10mV (SCE) toward the nobler-side potential when compared with the corresponding corrosion potentials (ECorr). It was also found that the lamellar morphology formed by alternated solvent-rich/intermetallics phases, which characterizes the microstructure of any alloy examined, provides an enveloping effect giving rise to a protective barrier against corrosion. Other microstructural features associated with the ratio of anode/cathode areas for each alloy examined are also discussed.

Corrosion properties and contact resistance of TiN, TiAlN and CrN coatings in simulated proton exchange membrane fuel cell environments

In this study, the contact resistance (CR) and electrochemical properties of TiN, CrN and TiAlN electron beam physical vapor deposition (EBPVD) coatings and their stainless steel 316L (SS316L) substrate were investigated in a simulated proton exchange membrane (PEM) fuel cell environment. The potentiodynamic polarization corrosion tests were conducted at 70 °C in 1 M H 2SO 4 purged with either O 2 or H 2, and the potentiostatic corrosion tests were performed under both simulated cathodic (+0.6 V vs. Ag/AgCl reference electrode purged with O 2) and anodic conditions (−0.1 V vs. Ag/AgCl reference electrode purged with H 2) for a long period (4 h). SEM was used to observe the surface morphologies of the samples after corrosion testing. All the TiN-, TiAlN- and CrN-coated SS316L showed a lower CR than the uncoated SS316L. While the corrosion performance of the coatings was dependent on the cathodic and anodic conditions, the CrN coating exhibited a higher (in the anodic environment) or similar (in the cathodic environment) corrosion resistance to the uncoated SS316L. Thus, the CrN-coated SS316L could potentially be used as a bipolar plate material in the PEM fuel cell environment. Although the EBPVD process greatly reduced number of pinholes in the coatings compared to other plasma enhanced reactive evaporations, future research efforts should be directed to eliminate the pinholes in the coatings for long-term durability in fuel cell applications.

Nanocrystalline soft ferromagnetic Ni–Co–P thin film on Al alloy by low temperature electroless deposition

Soft ferromagnetic ternary Ni–Co–P films were deposited onto Al 6061 alloy from low temperature Ni–Co–P electroless plating bath. The effect of deposition parameters, such as time and pH, on the plating rate of the deposit were examined. The results showed that the plating rate is a function of pH bath and the highest coating thickness can be obtained at pH value from 8 to10. The surface morphology, phase structure and the magnetic properties of the prepared films have been investigated using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and vibrating magnetometer device (VMD), respectively. The deposit obtained at optimum conditions showed compact and smooth with nodular grains structure and exhibited high magnetic moments and low coercivety. Potentiodynamic polarization corrosion tests were used to study the general corrosion behavior of Al alloys, Ni–P and Ni–Co–P coatings in 3.5% NaCl solution. It was found that Ni–Co–P coated alloy demonstrated higher corrosion resistance than Ni–P coating containing same percent of P due to the Co addition. The Ni–Co–P coating with a combination of high corrosion resistance, high hardness and excellent magnetic properties would be expected to enlarge the applications of the aluminum alloys.

Corrosion behaviour of highly alloyed stainless steels in mixed chloride and fluoride aqueous solutions

AbstractLaboratory weight loss and cyclic potentiodynamic polarization corrosion tests were performed on two types of corrosion resistant alloys, a duplex alloy (ferritic‐austenitic stainless steel) and two austenitic stainless steels, in mixtures of chloride (3000, 9000 and 15000 ppm) and fluoride (4800 and 15000 ppm) ions at pH 3. Two temperatures were tested, 60 and 70°C. The electrochemical results indicate that the duplex stainless steel presents high corrosion resistance. Weight loss results show low corrosion rates of the two types of stainless steels after 60 days exposure. Sonic pits‐crevices were found under the corrosion crust deposits on the duplex stainless steel.

Corrosion testing by potentiodynamic polarization in various electrolytes

The effect of different electrolytes on the results from potentiodynamic polarization corrosion testing was studied for nine different dental alloys. In general, the difference in the results was greater between certain alloys using the same electrolyte than between the electrolytes with the same alloy. However, there were some differences between the electrolytes, most pronounced when testing dental amalgams. The electrolyte consisting of 1% NaCl seemed to offer the most corrosive environment. Darvell's and Fusayama's solutions were much less corrosive, at least for dental amalgam specimens. With regard to the ranking by corrosion sensitivity of the amalgams, only the results obtained by using Fusayama's solution were consistent with the clinical experience of the materials.

Use of potentiodynamic polarization technique for corrosion testing of dental alloys

The number and in particular the diversity in types and composition of alloys used in dentistry are increasing, thus enhancing the need for predictive corrosion testing. No corrosion test is generally accepted as being both applicable to and relevant for all dental alloys. However, some methods have gained a certain recognition, and among these are the potentiodynamic polarization techniques. The purpose of the present work was to study the application, the reproducibility and the influence of some methodological variables on the results of potentiodynamic polarization corrosion testing. Embedded specimens of 18 different dental alloys, representing all major types, were subjected to anodic polarization scan within the potential range of -700 mV to 1000 mV (SCE). Artificial saliva, with and without organic compounds, and sodium sulfide solution were used as electrolytes. The results were processed on a microcomputer using locally developed software. The curves of current density versus potential showed fair reproducibility, with great differences between some of the alloys, showing a clear relationship to nobility or passivity of the alloy. There were marked differences between the results obtained in artificial saliva and in sodium sulfide solution, while addition of organic components to the artificial saliva only had a minor effect. The potentiodynamic polarization corrosion test supplies detailed information such as anodic charge, and open circuit, rupture, and passivation potential. Furthermore, it indicates the passive range and sensitivity to pitting corrosion. These are all useful when evaluating the corrosion properties of a dental alloy. An analysis of variance of the results in this study showed that possible differences between the alloys were clearly detectable with this method. However, for alloys releasing non-ionic products during corrosion/degradation, the method may be inappropriate. It is thus concluded that the method appears applicable as an in vitro corrosion test for most dental alloys, with the possible exception of amalgams.