Potentiodynamic Polarization Corrosion Tests Research Articles

Laser powder bed fusion of pure copper electrodes

This study explores the fabrication and characterization of a pure copper electrode for an EDM equipment using laser powder bed fusion (LPBF) and comparing its performance with an original cast sample. The microstructural, mechanical, electrical, thermal, and corrosion characteristics of the samples were analyzed. The microstructure of the additively manufactured (AM) sample exhibited superior mechanical properties, with an 18 % increase in ultimate tensile strength and more than two times greater elongation in comparison with those of the cast sample. Moreover, the electrical and thermal conductivity coefficients of the AM sample were found to be consistent with industry standards as 5.52 × 107 S/m and 361 W/mK, respectively. Additionally, the potentiodynamic polarization corrosion test results of the AM sample further exhibited superior corrosion resistance in terms of the corrosion potential particularly in a 3.5 % NaCl environment. Advanced electron microscopy techniques were used to investigate the differences in the properties of the AM and cast samples and further shed light on the superior properties of the LPBF counterpart. Despite challenges in manufacturing pure copper components through LPBF, this study demonstrates the feasibility of producing a functional part that competes effectively with cast counterparts and excels in certain aspects.

Corrosion behavior of the AlSi5Cu2Mg alloy with varying Zr addition

The aim of this paper was to analyze the impact of varying zirconium additions (0.05; 0.10; 0.15 and 0.20 wt. % Zr) on corrosion behavior of the AlSi5Cu2Mg aluminum alloy. Potentiodynamic polarization corrosion tests in 3.5 % NaCl solution demonstrated that the addition of Zr improved the thermodynamic corrosion stability of the AlSi5Cu2Mg alloy by shifting the corrosion potential to more positive values for all as-cast samples. The addition of Zr to the as-cast alloys also improved corrosion kinetics by lowering the corrosion current density.

Effect of carbon addition on dissolution behavior of aluminum alloy sacrificial anode

Using potentiodynamic polarization and immersion corrosion and sacrificial anode material discharge performance testing methods studied the dissolution behavior of aluminum anode material in the working condition of simulated Northwest oilfield corrosion conditions. The research results show that carbon can reduce the corrosion potential of aluminum anode material and anode current density increase, which can improve the material corrosion dissolution performance. Immersion corrosion test results show that with the carbon content in ascension, to enhance the anode material of aluminum anode material of uniform dissolving ability, passivation phenomenon was significantly suppressed. Adding carbon anode materials to add up the uniform’s ability to dissolve, eliminate the phenomenon of local corrosion of anode material and the discharge efficiency is greatly increased, effectively solve the aluminum anode material in high temperature environment to serve the current efficiency degradation of field engineering problems.

Role of dew points and Fe pre-coats on the galvanizing and galvannealing of dual phase steel

In this study, the galvanizing and galvannealing ability of dual phase steel sheet (DP 590), with and without Fe pre-coatings, is investigated with varying dew points using a hot dip process simulator (HDPS). Good quality defect free adherent galvanized coating on the substrate surface is obtained by appropriate selection of the inter-critical annealing atmosphere consists of N2-5%H2 gas mixture with +10 °C dew point without substrate pre-coating. However, the production of defect-free coating on DP 590 substrates is highly challenging when the substrates are without any pre-coating. It is observed that the selective oxidation of manganese on the substrate surface during intercritical annealing is primarily responsible for the appearance of bare spots on the galvanized surface in case of the coated specimen produced without pre-coating. A significant improvement in the reactive wetting behaviour between the liquid zinc alloy and pure Fe results in defect free adherent coatings (both galvanized and galvannealed) with electrodeposited Fe pre-coating on the substrate surface irrespective of dew points. Both the galvannealed specimens prepared with and without iron pre-coatings, exhibit partial passive-active metal characteristics in potentiodynamic polarization corrosion test. Iron pre-coating on the substrate surface is observed to improve the quality of galvannealed coatings by reducing defects and enhancing the formation of more compact and dense delta (δ) phase compared to galvannealed coatings produced without pre-coating under identical conditions. This leads to the improvement in corrosion resistance of galvannealed coating produced with pre-coating by lowering the corrosion potential and corrosion current density compared to that of galvannealed specimens produced without iron pre-coating.

Corrosion resistance of thermal-pulsed Inconel 625 MIG/MAG weld overlays

The deposition of Inconel 625 can be performed by MIG/MAG (Metal Inert Gas/Metal Active Gas) welding process. Despite resulting in larger dilution than other welding methods, MIG/MAG has the advantage of a high production capacity. The present work aimed to study the use of a variant of the MIG/MAG process known as MIG/MAG Double Pulse (MIG/MAG-DP), where the variation of the welding current in the form of pulses can alter the microstructure of the deposits. The effects on corrosion resistance of the macrogeometry and microstrucure of Inconel 625 weld overlays onto low carbon steel substrates were evaluated via cyclic potentiodynamic polarization corrosion tests under two test temperatures (25 °C and 60 °C). The results showed that the MIG/MAG-DP process produced weld overlays with higher dilution (almost twice of that observed for conventional MIG/MAG). Moreover, MIG/MAG-DP resulted in more refined microstructure; the spacing between the dendritic secondary arms was around 49% smaller than for conventional MIG/MAG. This had a negative impact on the corrosion resistance of the deposits at both temperatures and increased the susceptibility of the deposits to crevice corrosion. Therefore, the use of MIG/MAG-DP, although often a positive strategy in welding operations, is not a good route for depositing high corrosion resistance deposits.

In vitro corrosion-fatigue behavior of biodegradable Mg/HA composite in simulated body fluid

Magnesium and its composites as biodegradable materials offer especial capabilities to be used as bio-absorbable implants. However, their poor corrosion and fatigue properties in the physiological environment can restrict their applications. In this study, corrosion-fatigue tests have been performed on the extruded magnesium and magnesium/hydroxyapatite (Mg/HA) composites in a high cycle regime. To produce the composites, pure magnesium was reinforced by 2.5 wt.% and 5 wt.% of hydroxyapatite submicron particles using an electromagnetic-mechanical stirring method and hot extrusion process. The experimental density measurement exhibits that the porosity increases in the extruded samples with more hydroxyapatite particles. To investigate the corrosion and corrosion-fatigue behavior of the specimens, simulated body fluid (SBF) was used during in vitro tests. The results of the potentiodynamic polarization corrosion test show that the composite with 2.5 wt.% of hydroxyapatite (Mg/2.5 wt.% HA) and the pure magnesium specimen exhibit the highest and the lowest corrosion resistance, respectively. Regarding the elemental mapping analysis of the corroded samples, this behavior could be due to the formation of strong phosphorus-calcium based layers on the composite surface. The results obtained from the mechanical tests indicate that Mg/5 wt.% HA offered the highest tensile and compressive yield strengths, as well as the most promising high cycle fatigue behavior. During the corrosion-fatigue test, the simultaneous effects of fatigue and corrosion damages led to a similar corrosion-fatigue behavior in both composites. The fracture surfaces of the corrosion-fatigue samples suggest that the cracks are initiated in the corroded regions of the samples surface, which reduces the crack initiation step and subsequently decreases the fatigue life. In comparison with the pure magnesium, both composites exhibit more promising corrosion and corrosion-fatigue behaviors with a significant fatigue life improvement in the physiological environment.

Interfacial Investigation of St13/Molten Zn–5% Al and Corrosion Behavior of Formed Layer via Hot-Dip Process

In the present study, the effect of temperature and duration of hot-dipping on structural properties, hardness, and corrosion resistance of Zn–5% Al coatings on ST13 low-carbon steel has been investigated. The samples were dipped in a molten metal bath at temperatures of 440, 480 and 520°C, during 20, 50 and 70 seconds. To investigate the microstructure and properties of samples, scanning electron microscopy, energy dispersive X-ray spectrometry, microhardness measurements, and potentiodynamic polarization corrosion tests were used. The results showed that the coating structure is an eutectic layer at 440°C, and at the interface of the substrate and the coating a thin inhibitory layer is formed that prevents the diffusion of the substrate atoms into the coating and from the molten bath into the substrate. With an increase of temperature to 480 and 520°C, with the diffusion of iron atoms of the substrate and of the molten bath, a triple metallic layer of Al–Fe–Zn forms, and the thickness of the coating increases. As the dipping time increases, the number of intermetallic particles in the coating also increases. At higher temperatures, the hardness went up from 86 to 121.73 Hv and the corrosion rate—from 7.381 to 37.53 Mpy. hot dip, Zn–5% Al coating, microstructure, intermetallic, corrosion

Development of Nanostructured Ni–Fe Alloy Coatings; Characterisation and Corrosion Analysis

The present investigation deals with the electrofabrication of nanostructured Ni-Fe alloy coatings on a mild steel using sulfate bath. The electrolytic bath composition and the current density of the coatings were optimized. Composition analysis by energy dispersive X-ray spectroscopy revealed that the Ni–Fe alloy coatings are of anomalous type. Potentiodynamic polarization corrosion test and electrochemical impedance spectroscopy methods in 3.5% NaCl solution direct towards the lowest corrosion rate at 4 A dm–2. Hardness and roughness of the coatings were evaluated using Vickers hardness test and atomic force microscopy, respectively. The surface morphological analysis of the coatings was characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy. The phase structure, the texture coefficient, and the crystallite grain size of the coatings were calculated and studied using X-ray diffraction.

Effect of Mechanical Properties and Corrosion Behaviour of Martensitic Stainless Steel 410 1.6mm Butt Welded by Plasma Arc Welding

Plasma Arc Welding (PAW) is one of the important arc welding processes used in electronics, medical, automotive and aerospace industries due its high accuracy and ability of welding any hard materials which is more tolerant to joint misalignment than Laser Beam Welding (LBW) at a lower cost. Thickness of 1.6mm plates were used to obtain full penetration and a strong joint with a very narrow Heat Affected Zone. The present study deals with the effect of mechanical and corrosion resistance properties of butt welded 1.6 mm thick martensitic stainless steel-similar (SS410 and SS410) joints made by plasma arc welding technique. Similar butt Welded joints were analyzed by using mechanical (Bend test, Erichsen cup test, Tensile test) characterization methods. Their corresponding corrosion resistance properties were also investigated by potentiodynamic polarization corrosion testing technique. The tensile strength was found to be 341 MPa for similar SS410 weld. During tensile test the failure occurred on the base metal on both similar joints Keywords: SS304; SS410; PAW; Butt weld; Erichsen Cup Test; Microstructure.

Effect of cold rolling on the microstructural, magnetic, mechanical, and corrosion properties of AISI 316L austenitic stainless steel

This study has evaluated the effect of different levels of cold rolling (from 0 to 50%) on the microstructural, magnetic, and mechanical properties and the corrosion behavior of 316L austenitic stainless steel in NaCl (1 mol/L) + H2SO4 (0.5 mol/L) solution. Microstructural examinations using optical microscopy revealed the development of a morphological texture from coaxial to elongated grains during the cold-rolling process. Phase analysis carried out on the basis of X-ray diffraction confirmed the formation of the ferromagnetic α′-martensite phase under the stresses applied during cold rolling. This finding is in agreement with magnetic measurements using a vibrating sample magnetometer. Mechanical properties determined by tensile and Vickers microhardness tests demonstrated an upward trend in the hardness-to-yield strength ratio with increasing cold-rolling percentage, representing a reduction in the material’s work-hardening ability. Uniform and localized corrosion parameters were estimated via potentiodynamic polarization corrosion tests and electrochemical impedance spectroscopy. In contrast to the uniform corrosion, wherein the corrosion current density increased with increasing cold-working degree because of the high density of microstructural defects, the passive potential range and breakdown potential increased by cold working, showing greater resistance to pit nucleation. Although pits were formed, the cold-rolled material repassivation tendency decreased because of the broader hysteresis anodic loop, as confirmed experimentally by observation of the microscopic features after electrochemical cyclic polarization evaluations.

Evaluation of the Influence of Surface Finishing on the Corrosion Resistance of HVOF Applied Inconel 625 Coatings on Steel

In this work, the corrosion resistance of Inconel 625 coatings applied to AISI 4140 steel plates was evaluated. Coatings were produced by High Velocity Oxygen Fuel (HVOF) by use of two different equipment which use either kerosene (liquid) or propane (gas) as fuel. The resulting coatings were evaluated in two conditions: as-deposited and after a surface finishing process by grinding. Residual stress distributions in the coatings were characterized by X-ray diffraction and their morphology was verified through metallography and roughness measurements. Potentiodynamic polarization corrosion testing complemented their analysis. The results show a strong influence of the surface finishing process on the corrosion performance of the coatings.

Enhancement of mechanical properties and corrosion resistance of friction stir welded joint of AA2014 using water cooling

An investigation on the microstructure, mechanical properties, and corrosion behavior of friction stir welded joint of AA2014 in natural cooled (NC) and water cooled (WC) conditions have been reported. Optical microscopy, field emission scanning electron microscopy (FESEM) with Energy dispersive X-ray spectroscopy (EDS), Vicker's microhardness, tensile testing, X-ray diffraction (XRD), and electrochemical potentiodynamic polarization corrosion test (Tafel curve) were carried out to characterize the friction stir weld joints in both the cooling conditions. Water cooling resulted in higher strength and microhardness of friction stir weld joint compared to the natural cooling. The width of heat affected zone was reduced by the use of water cooling during friction stir welding (FSW) and minimum hardness zone was shifted towards weld center. The corrosion test was performed in 3.5% NaCl solution. Corrosion resistance of water cooled joint was found higher than natural cooled FSW joint. The precipitation behavior of weld nugget and heat affected zone impacts the corrosion resistance of FSW joint of AA 2014. Hardness, tensile, and corrosion properties of FSW joints produced under NC and WC conditions have been discussed in the light of microstructure.

Mechanical properties, wear and corrosion behavior of copper matrix composites reinforced with steel machining chips

The mechanical properties, wear and corrosion behavior of copper matrix composites reinforced with steel machining chips was investigated in this research. Steel machining chips with chip size range of 105μm and below were utilized to develop stir cast copper matrix composites having 5, 7.5 and 10wt% of the chips as reinforcement. Unreinforced copper and 10wt% alumina reinforced copper matrix composites were also prepared for control experimentation. Hardness and tensile properties evaluation, wear test, potentiodynamic polarization corrosion tests, and optical microscopy; were used as basis to characterize the composites produced. The results show that the addition of steel machining chips in copper resulted in significantly low porosity levels in the copper matrix composites compared with the use of alumina as reinforcement. The mechanical properties (hardness and tensile properties) and wear resistance were also observed to improve with the use of the steel machining chips as reinforcement. The corrosion susceptibility in 3.5wt% NaCl solution were observed to be more intense for the unreinforced copper and the alumina reinforced composite grade compared with the steel chips reinforced copper matrix composites. But in 0.3M H2SO4 solution, no consistent corrosion trend was observed although the corrosion resistances of all the composite grades produced were superior to the unreinforced copper. The results demonstrate the capacity of steel machining chips to serve as a reliable cost effective and technically efficient reinforcement material for the development of copper matrix composites.

PEO Ceramic Coating on Mg-10%wt. Zn for Potential Biological Application

Magnesium-zinc (Mg-Zn) alloys are strong candidates as medical implant materials due to their good biocompatibility and relatively high strengths. To manipulate the degradation of Mg-Zn alloy in the human body, a plasma electrolytic oxidation (PEO) treatment was applied to Mg-10%wt. Zn in this study because it produces a coating that is non-harmful to the human body and the process is inexpensive and environmentally friendly. Potentiodynamic polarization corrosion tests, performed in a simulated body fluid (Hanks’ Balanced Salt Solution) were applied to the coated and uncoated Mg-Zn samples. The results of the testing showed that the coated Mg-Zn exhibited higher corrosion resistance than the substrate. With the PEO coating thickness of 7.2 microns, the corrosion current density was reduced by 1.00 μA/cm2 from the uncoated Mg-Zn respectively, indicating a significant reduction in the degradation rate between pure Mg-Zn and coated Mg-Zn from 7.0 to 3.7 kg/year. A pin-on-disc tribometer was employed to measure the coefficient of friction (COF) for the coated and uncoated Mg-Zn samples, lubricated with and without Hanks’ solution. The measured COF of the coated sample was very low (averaging to be about 0.22 under the lubricated condition) and comparable to that of the substrate which exhibited an averaged COF of 0.13 under the lubricated condition.

Internal passivation of Al-based microchannel devices by electrochemical anodization

Metal-based microchannel devices have wide-ranging applications. We report here a method to electrochemically anodize the internal surfaces of Al microchannels, with the purpose of forming a uniform and dense anodic aluminum oxide (AAO) layer on microchannel internal surfaces for chemical passivation and corrosion resistance. A pulsed electrolyte flow was utilized to emulate conventional anodization processes while replenishing depleted ionic species within Al microtubes and microchannels. After anodization, the AAO film was sealed in hot water to close the nanopores. Focused ion beam (FIB) sectioning, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) were utilized to characterize the AAO morphology and composition. Potentiodynamic polarization corrosion testing of anodized Al microtube half-sections in a NaCl solution showed an order of magnitude decrease in anodic corrosion current when compared to an unanodized tube. The surface passivation process was repeated for Al-based microchannel heat exchangers. A corrosion testing method based on the anodization process showed higher resistance to ion transport through the anodized specimens than unanodized specimens, thus verifying the internal anodization and sealing process as a viable method for surface passivation of Al microchannel devices.

Effects of polydopamine coating on the bioactivity of titanium for dental implants

The effect of polydopamine coated titanium such as surface roughness, wettability, cell growth and toxicity, and corrosion resistance. The polydopamine-coated titanium was successfully prepared from dopamine solution and bright polydopamine granules were randomly distributed on titanium surface after coating process. The surface roughness was not significantly decreased in the pure titanium (P>0.05), but significantly decreased (P<0.05) in the spark anodized titanium after the dopamine coating treatment. The contact angle of polydopamine-coated titanium surface was found to be lower than that of the untreated titanium surface. At the potentiodynamic polarization corrosion test, polydopamine-coated titanium has better corrosion-resistance than untreated titanium. The resistance of cytotoxicity is decreased by dopamine coating surface treatment (P<0.05). Findings from this research suggested that polydopamine coating offer a versatile approach for the titanium surface modification.

Characterization of Oxide Film by Vanadium Based Anodic Oxidation Coating

An oxide film was prepared on AZ91D magnesium alloy by anodizing in solution containing sodium metavanadate (NaVO3). The corrosion resistance of the AZ91D magnesium alloy was investigated at fixed current density 10 mA/cm2for 5 min with different concentration of solution in the range of 0 1.0 g/l. The surface morphology, cross section morphology, phase structure, and surface roughness of oxide film were studied by optical microscope, scanning electron microscope (SEM) and energy dispersive spectrometry (EDS), atomic force microscope (AFM) and potentiodynamic polarization technique and corrosion test, respectively.

Corrosion Resistance by Sodium Metavanadate for AZ91D Magnesium Alloy

An oxide film was prepared on AZ91D magnesium alloy by anodizing in solution containing sodium metavanadate (NaVO3). The corrosion resistance of the substrate was investigated at a fixed current density 10 mA/cm2for 5 mins with different concentration of solution in the range of 0 – 1.0 g/l. The surface morphology, phase structure and corrosion resistance of oxide film were studied by optical microscope, scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) and X-ray diffractometer (XRD), potentiodynamic polarization technique and corrosion test.

Titanium-Aluminum Oxide Coating on Aluminized Steel

In this study, a plasma electrolytic oxidation (PEO) process was used to form titanium-aluminum oxide coating on aluminized steel. The present work was mainly to study the effects of treatment time of PEO process on properties of the titanium coating. A potentiodynamic polarization corrosion test was employed to investigate the corrosion resistance of the coating. The friction coefficient and wear resistance of the coating were studied by using pin-on-disc test. The thermal transfer behaviors of uncoated and PEO-coated aluminized steels were also studied. It could be seen that treatment time of PEO process significantly influenced the properties of the titanium oxide coating. Samples with a longer treatment time had a better performance for corrosion and wear protection. This paper demonstrated different treatment time could alter the surface behavior of the coating material. Keywords—Corrosion, plasma electrolytic oxidation, thermal property, titanium-aluminum oxide.

Surface characteristics of mussel-inspired polydopamine coating on titanium substrates

Mussel adhesive proteins are non-toxic, biodegradable and have low immunogenic qualities that make them highly attractive for medical purposes compared with man-made materials. 3,4-DOPA, which is a dopamine precursor, is a critical element for achieving mussel-like adhesive properties. In present study, polydopamine was coated onto the titanium surfaces by dipping in a 2 mg/mL dopamine solution in 10 mM Tris-HCl buffer at pH 8.5. EDX element analysis and Raman spectroscopic analysis of the surface were conducted to verify the formation of polydopamine. The surface characteristics of polydopamine-coated titanium plates were observed by SEM and AFM. Hydrophilicity and corrosion-resistance were also evaluated by static contact angle measurements and potentiodynamic polarization corrosion tests. The absorption intensity for pH-induced polymerization rapidly increased for the initial four hours and thereafter smoothly increased. EDX element analyses revealed that the content of carbon and oxygen increased and the content of titanium decreased after the coating process. In the Raman spectra, polydopamine resulted in two new peaks at approximately 1 370 and 1 570 cm−1 resulting from the stretching and deformation of catechol. Microstructural features revealed that nanometer-sized bright granules were randomly distributed after coating, and these nanoparticles grew with increased coating time. The Ra values of polydopamine-coated titanium plates were showed to increase with coating time. Compared to the pure titanium curve, the inflection point of polydopamine-coated titanium was located at a higher corrosion potential and lower corrosion current density. Findings from our research suggested that polydopamine coatings offer a versatile approach for titanium surface modification.