Lower Corrosion Potential Research Articles

Facile synthesis of nano silica-based coating on API5L-x80 steel to achieve ultra non-wetting surface and its corrosion resistance

A facile and acceptable way for arrangement of non-wetting ultra-hydrophobic silica coatings is proposed in this work. The X80 steel samples with the dimension of 10 × 10 × 2 mm were used as the base metal. Commercially silica nanoparticles were modified using alkoxide organosilane as an active modifying agent. The ultra-hydrophobic silica coatings with a water contact angle of 142° were achieved (ultra-high degree of contact angle). The prepared silica coatings exhibit ultra-hydrophobicity and excellent corrosion behaviors under 3.5 wt% NaCl immersion testing conditions, which surfaces with 2.0% and 2.5% of hydrophobic silica specimens show a low corrosion potential and current, significantly. The corrosion resistance of the samples was evaluated by the electrochemical impedance spectroscopy technique also the microstructure, and surface topography of the samples was evaluated with scanning electron microscopy and Fourier transform infrared, respectively. This coating method is expected such a convincing process technology against fabricating self-cleaning coatings for the encouraging industrial implementation.

Studies on corrosion behavior of AISI 316L cold metal transfer weldments in physiological solutions

Evaluating the mechanical integrity and corrosion performance of welded joints is vital to replace the malfunctioning parts in human body. This research aims to study the effect of Cold Metal Transfer (CMT) process on the corrosion behavior of austenitic stainless steel (AISI 316L) weldments in physiological solution. ER316L filler wire is used to weld thin sheets of 2mm to butt joint configuration. Optical microscopy and Scanning electron microscopy (SEM) are used to study the microstructural evolution in base metal (BM), heat affected zone (HAZ) and weld metal (WM). For determining the phases in BM and WM, X-ray diffraction (XRD) spectrums are captured. WM microstructure illustrated the presence of equiaxed grains while columnar dendrites were observed at HAZ. Energy Dispersive X-Ray Spectroscopy (EDS) analysis highlighted the increase in wt. % of Fe and Cr in WM due to the thermal variations. EDS elemental mapping revealed uniform distribution of Cr, Mo and Fe elements in the WM. AISI 316L WM exhibited higher tensile strength and reduced ductility compared to BM. Micro-hardness measurements showed higher hardness at the WM as result of the increased ferrite content and ductile mode of fracture was characterized with dimples and micro voids. During Corrosion test, the WM and the BM revealed lower corrosion potential and the pitting tendency is relatively less than HAZ. The delta ferrite (δ) formation in the HAZ and WM did not affect the corrosion behavior significantly as confirmed from Tafel scans and Nyquist plots. The corrosion rate is within the acceptable range, ie. First level for WM (<1 mpy) and second level for BM and HAZ (1-5 mpy), respectively.

Bone Tissue Properties after Lanthanum Zirconate Ceramics Implantation: Experimental Study

Background. The ceramic based on lanthanum zirconate is characterized by optimal mechanical characteristics, low corrosion potential and the absence of cytotoxicity. Thus, the possibility of its use as bone substituting material is currently studied. The purpose of the study was to determine the mechanical, morphological and x-ray spectral characteristics of bone tissue after implantation of ceramic material based on lanthanum zirconate. Materials and methods. The experiment was conducted on 27 female guinea pigs of a single line, divided into 3 groups of 9 animals each. In the main group (LZ), lanthanum zirconate rods were implanted. In the comparison group (b-TCP), fixation was performed with b-tricalcium phosphate rods. In the native control group (NC) no surgical procedures were performed. A fracture was created in distal metadiaphysis area of femur using open osteoclasia. Animals were hatched 4, 10, and 25 weeks after the start of the experiment. Bone tissue features were studied in the perifocal region. The following methods were used: uniaxial compression, scanning electron microscopy (SEM), energy dispersive x-ray microanalysis (EDxMA). The statistical analysis was performed using the Mann-Whitney test. Results. The architectonics of the newly formed bone in the LZ group appeared as a developed lacunar tubular network. The structural components of the extracellular matrix were oriented along the bone functional load vectors. The Ca/P ratio in the periimplant region of the bone in the LZ group was significantly higher than in the b-TCP and NC groups. This may indicate a high strength of the newly formed bone. Mechanical testing showed that the strength and performance of the system of “lanthanum zirconate – bone” under uniaxial compression exceeded the similar indicators in the b-TCP group. Conclusion. The synthesized new material based on lanthanum zirconate seems promising for use in traumatology and orthopedics. Although, additional studies are needed to optimize these implants integration into bone tissue.

A discussion on evaluation criteria for crevice corrosion of various stainless steels

In this study, crevice corrosion performances of a newly developed LDSS 2002 and three commercial stainless steels (AISI 304, AISI 316L and DSS 2205) were investigated and discussed. Crevice repassivation potential (ER,CREV), which was measured by the potentiodynamic-galvanostatic-potentiodynamic (PD-GS-PD) test, was applicable to crevice corrosion evaluation of 304 and 316L stainless steels. However, much lower ER,CREV values were obtained for DSS 2205 and LDSS 2002. These abnormal ER,CREV values for duplex stainless steels may be related to the selective attack of the less corrosion-resistant phase, the lower corrosion potential in the crevice-like solution, and more crevice corrosion sites in the PD-GS-PD test. A critical chloride concentration of crevice corrosion (CCCCREV) measurement was introduced for crevice corrosion evaluation of various stainless steels. The derived CCCCREV was proved to be a valid criterion for crevice corrosion evaluation of both the austenitic and duplex stainless steels. An order of crevice corrosion resistance of AISI 304 ≈ LDSS 2002 < AISI 316L < DSS 2205 was suggested, which agreed well with the orders of pitting resistance equivalent number and critical crevice index of the less corrosion-resistant phase in each material.

Two-dimensional numerical analysis of differential concentration corrosion in seawater pipeline

PurposeThe purpose of this paper is to develop a new two-dimensional differential concentration corrosion mathematical model based on the knowledge that oxygen distribution on the surface of the seawater pipe is two-dimensional.Design/methodology/approachThe ionic conductive layer element near the pipeline wall is regarded as the research object, and the finite element method is adopted to obtain the oxygen distribution in the layers and the natural corrosion potential and natural corrosion current of each element. Then, these element sets are regarded as a whole circuit and each element as a node on the circuit; the equation is satisfied by the corrosion potential after polarization is derived for each element according to Kirchhoff’s second law.FindingsMatlab is used to solve the equation sets, and the overall corrosion current is calculated. The results are quite different from those considered without the differential concentration corrosion. If the differential concentration corrosion is not considered, the location with high oxygen concentration on the pipeline wall has a large corrosion potential and current. If corrosion is considered, the potential will cause polarization and the positions with original higher corrosion potential will produce anodic polarization. Meanwhile, the speed of corrosion also decreases. At the same time, the position with original lower corrosion potential will produce cathodic polarization, and the corrosion current is also increased, namely, the corrosion current and the potential will be homogenized.Originality/valueA two-dimensional model for the study of concentration corrosion is proposed creatively. Based on the knowledge of electricity, a discrete equation of corrosion potential after polarization is derived. The distribution of corrosion potential and corrosion current is obtained by solving the equation, and the mechanism of concentration corrosion is analyzed. The law of concentration polarization corrosion is also obtained.

Corrosion Behavior and Passive Film Characterization of Fe50Mn30Co10Cr10 Dual-Phase High-Entropy Alloy in Sulfuric Acid Solution

This study investigated the corrosion properties of a Fe50Mn30Co10Cr10 dual-phase high-entropy alloy (DP-HEA) in 0.1 M H2SO4 aqueous solution. The observed corrosion properties of the DP-HEA were compared with those of an equiatomic CoCrFeMnNi high-entropy alloy (HEA). Moreover, a passive film formed on the surface of the DP-HEA in an acidic environment was directly imaged and characterized for the first time through high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Both alloys exhibited typical active–passive behaviors in the potentiodynamic polarization test and presented similar passive current densities. The HR-TEM results revealed that the anodic passive films formed on the surfaces of the two alloys had similar thicknesses (3–5 nm). However, potentiodynamic polarization measurements showed that the DP-HEA had a higher corrosion current density and lower corrosion potential than did the HEA. XPS revealed that the anodic passive film formed on the DP-HEA contained a lower ratio of Cr2O3/Cr(OH)3, which led to poor corrosion resistance properties, as demonstrated by the potentiodynamic polarization measurements and electrochemical impedance spectroscopy.

Microstructure, mechanical and corrosion properties of cryorolled-AA5052 at various solution treatment temperatures

Initial solution treatment (ST) of aluminium alloys prior cryorolling (CR) enhances the ultrafine grain structure formation hence, improving their mechanical and corrosion properties. However, determining the appropriate ST temperature is crucial to obtain the optimum properties. In this work, ST followed by cryorolling of AA 5052 alloy was performed at varying temperatures; 480 °C, 510 °C and 540 °C. Mechanical and microstructural characterization of the cryorolled samples with and without ST and the base metal were performed using Vickers hardness tester, universal tensile testing machine, FESEM, EBSD and HRTEM. All the ST cryorolled samples showed the finer structure and better mechanical and corrosion performances than those without ST and the base metal. The smallest crystallite size and lattice strain achieved were 24.88 nm and 3.86 × 10−3 respectively at 540 °C. The hardness, yield and tensile strength increased with increasing the ST temperature with the highest values of 85.2 Hv, 254.82 MPa and 303.35 MPa, respectively, at 540 °C. Cryorolled sample solution treated at 540 °C also showed the highest corrosion resistance based on low corrosion current and high corrosion potential. The work gives the appropriate ST temperature at which improved microstructure, mechanical and corrosion properties of the cryorolled AA5052 can be obtained.

Effect of heat treatment on erosion–corrosion of Fe-based amorphous alloy coating under slurry impingement

In order to investigate the effect of vacuum heat-treatment (VHT) on the erosion−corrosion performance of Fe-based amorphous alloy coating (Fe-AAC) under alkaline sand-containing NaCl slurry impingement, Fe48Cr15Mo14C15B6Y2 at.% amorphous alloy coatings were first prepared via a high-velocity air fuel (HVAF) spraying process and then vacuum heat-treated at several different temperatures. Experimental results show that the fraction of the amorphous phase in the coating decreases with increasing VHT temperature. The heat-treated coatings exhibit a higher hardness of ∼994 HV0.1 with good wear resistance but lower corrosion potentials of ∼ -0.607 V and a larger corrosion current density of ∼7.98 × 10−6 A. Erosion−corrosion tests show that the mass loss increases as the temperature of the heat-treatment increases under the same conditions of slurry pH. However, as the slurry pH values increase, the mass loss of the sample treated at the same VHT temperature tends to decrease. The mechanism of erosion−corrosion failure of the Fe-AAC is the synergy of wear by fluidity particles on coatings and corrosion of corrosive media during erosion.

Corrosion and tribocorrosion behaviours of AISI 321, AISI 431 and FDMA borided and non-borided steels

Corrosion and tribocorrosion behaviours of non-borided and borided steel materials were evaluated under sliding contact in a 3.5 wt% NaCl solution, using an alternative tribometer integrated with a potentiostat for electrochemical control. Alloy-steel samples were borided by a powder-pack boriding process during 1 h at 950 °C. Microstructural examinations and phase analysis were performed employing Scanning Electron Microscopy (SEM) and x-ray diffraction. The surface profiles of wear tracks were obtained using a high resolution surface profilometer. Under corrosion conditions, it was found that a negative effect of boriding treatment was observed in the corrosion resistance of the investigated steels due to the presence of porosity and microcracks within FeB and Fe2B coating layers. On the other hand, the tribocorrosion tests indicated the positive effect of boride coating which induced a shift of the polarization curves of the borided steels to higher corrosion potentials contrary to the Tafel polarization curves of the non-borided steel materials which shifted to lower corrosion potentials. Moreover, even though the borided steels presented lower corrosion performances, the synergistic effect between corrosion and wear acting together resulted in a decrease of their coefficient of friction (COF) values and material losses with respect to the non-borided steel materials. In addition, the line profile of their surfaces exhibited less pronounced wear behaviour showing shallowed wear depth leading subsequently to a lower wear volume and loss compared to the non-borided steel materials. Microscopic observations revealed that wear-induced corrosion was more dominant in the corrosion-wear synergism.

Corrosion Resistance of Zn-Al-Mg Alloys with Hypoeutectic Microstructure

Zn-Al-Mg alloys with hypoeutectic microstructure were melted through a high frequency induction furnace. The content of aluminum and magnesium in the alloys were between 1% to 2%. Scanning electron microscopy (SEM) was utilized to analyze microstructure and phase, respectively. Effect of alloying element contents on corrosion resistance was studied. Results show that the Zn-Al-Mg alloys are almost covered by primarily solidified Zn rich block phase and fine lamellar binary and ternary eutectic microstructure exist between the Zn rich phase. The corrosion resistance was characterized through electrochemical test which indicates that increasing Al and Mg content in the Zn-Al-Mg alloys decline corrosion current density. For alloys with 1% Al, more magnesium means lower corrosion potential. For alloys with 2% Al, however, more magnesium suggests higher corrosion potential. In Nyquist curves of electrochemical impedance spectroscopy (EIS) test, Warburg impedance portion could be found for all alloys. With increasing alloying elements content in the Zn-Al-Mg alloys, charge transfer resistance in higher frequency remarkably increase, which implies higher corrosion resistance.

A reactive-sputter-deposited TiSiN nanocomposite coating for the protection of metallic bipolar plates in proton exchange membrane fuel cells

To meet the needs of corrosion resistance and electrically conductivity for metallic bipolar plates that are employed in proton exchange membrane fuel cells (PEMFCs), a TiSiN nanocomposite coating was fabricated on to a Ti–6Al–4V substrate using reactive sputter-deposition through the double cathode glow discharge plasma technique. The microstructure of the TiSiN coating comprised nanocrystallite TiN grains embedded in an amorphous Si3N4 matrix. Electrochemical measurements were employed to investigate the corrosion behavior of the TiSiN coating in the simulated operating environments of a PEMFC, specifically 0.5 M H2SO4 solution containing different HF concentrations (namely 2, 4 and 6 ppm) at 70 °C pumped with H2 at the anode and air at the cathode. With increasing HF concentration, a higher corrosion current density and lower corrosion potential were observed from both the coating and the uncoated substrate, indicating that the addition of HF accelerated their corrosion rates under these conditions. Compared to the uncoated substrate, the TiSiN coating showed a markedly higher corrosion resistance at all HF concentrations. The passive film that formed on the TiSiN coating, with a resistance of the order of magnitude of ~107 Ω cm2, displayed good electrochemical stability and was less affected by changes in HF concentration. For the TiSiN coating, the values of interfacial contact resistance (ICR) were 14.7 mΩ cm−2 and 18.3 mΩ cm−2, respectively, before and after 2.5 h potentiostatic polarization with 6 ppm HF under cathodic conditions under a compaction pressure of 140 N cm−2. Both values are much lower than those for the bare substrate. Moreover, the TiSiN coating was shown to improve the hydrophobicity of Ti–6Al–4V that would help facilitate water management in the PEMFC operating environment. This coating, which exhibited excellent corrosion resistance, electro-conductivity and hydrophobicity, is therefore a promising material for protecting metallic bipolar plates from corrosive attack.

The removal of phosphates using electrocoagulation with Al−Mg anodes

The removal of phosphates, to levels below the detection limit, was achieved over a 30 to 60min period, depending on the initial phosphate concentration, with Al−Mg anodes in an electrocoagulation cell at 11.0mAcm−2 with a surface area to volume ratio of 11.7m−1. The Al−Mg alloy performed well in low chloride concentrations of 4.2mM NaCl and the complete removal of phosphates from two real water samples was achieved after a 15−min period. The removal efficiency, although depending on the initial pH, appears to depend on the evolution of pH during electrocoagulation with more efficient removal at a final pH of 7.5. Using the Freundlich adsorption model, the adsorption capacity, kF, was computed as 146mgg−1, corresponding to the adsorption of 146mg of phosphate per gram of the aluminium−hydroxy coagulant. The efficient removal of the phosphates was attributed to the low corrosion potentials and the lack of a passive region observed using polarisation and cyclic polarisation experiments, which in turn facilitate dissolution of the anode.

Contributions of corrosion and erosion in the erosion-corrosion of Sanicro28

Corrosion, erosion and synergism behaviors of Sanicro28 (UNS–N08028) stainless steel have been studied during erosion-corrosion using a slurry impingement rig. The erosive-corrosive slurry solution consisted of 3.5% NaCl saline water and 30 g/l SiO2 erodent particles. The erosion and erosion-corrosion tests were performed at jet velocities of 4, 6, 7.5, and 9 m/s under two impingement angles of 40 and 90°. The corrosion behavior of the alloy in both stagnant and erosion-corrosion conditions was studied by electrochemical impedance spectroscopy and polarization techniques and the synergy was calculated. The results showed that corrosion, erosion, erosion-corrosion, and synergy rates of the alloy increased as the impact velocity increased. An increase up to 104 times was observed in the corrosion rate during erosion-corrosion as compared with the stagnant condition. There were about 28 times increase in the corrosion rate and 25% decrease in the corrosion potential as the impact velocity increased from 4 to 9 m/s during the erosion-corrosion. A higher corrosion rate and a lower corrosion potential were also obtained at the normal incident compared with impingement angle of 40°. The removal rates showed a critical velocity of 6 m/s in both the erosion and erosion-corrosion conditions, however, the transition was not clear in the electrochemical results. It was found that the change of erosion wear due to corrosion was higher than the change of corrosion due to erosion under various conditions indicating that the synergy rate was highly dependent on the effect of corrosion on erosion.

Effectiveness of an intercritical heat-treatment on localized corrosion resistance at the microstructural boundaries of medium-carbon steels

The localized corrosion resistance at the microstructural boundaries of AISI 1045 carbon steels was accessed. Under KFM measurements, regions with low corrosion potentials were found at the pearlite colony boundary in the ferrite-pearlite structure and the prior austenite grain boundary in the martensite structure, and phosphorus was segregated in these regions. The localized corrosion resistance at these boundaries was improved via intercritical heat-treatment at 1023 K (the two-phase region of austenite and ferrite) after austenitizing, which may be attributable to the apparently homogenous dissolution of ferrite forming elements, such as phosphorus, in the ferrite phase during the treatment.

The role of bacterial biofilm and mechanical forces in modulating dental implant failures

Currently many assume that bacteria are the primary etiological factor associated with failure of titanium dental implants. However, emerging data indicates a possible role for mechanical forces in implant failure. This study is based on the hypothesis that the synergistic effect of mechanical forces and bacterial biofilm can lead to surface damage resulting in in vivo release of metallic particles. The primary aim of the study was to develop a dynamic fatigue test method for dental implants immersed in wet environments such as; (i) 0.01 M phosphate buffer saline (PBS); (ii) lactic acid (pH = 5); (iii) bacterial polyculture. Four dental implants each were subjected to fatigue loading from 45 N to 450 N at 4 Hz for 2 million cycles while immersed in (i) PBS (negative control); (ii) bacterial culture (test); and (iii) lactic acid (positive control). Post-testing, optical microscopy, x-ray photoelectron spectroscopy, and electrochemical corrosion tests were performed to evaluate the surface morphology, chemistry, and potential, respectively, of titanium implants. Post-testing, surface discoloration was evident in all three groups. However, the surface damage was further established in XPS analyses of test specimens, which showed that the interplay of bacterial biofilm and mechanical forces resulted in thinning of the TiO2. Lower corrosion potential (Ecorr) of the test specimens compared to positive and negative controls also illustrated damage to the oxide layer. However, other electrochemical parameters such as linear polarization resistance (LPR) and corrosion rate (CR) were comparable among the groups indicating the corrosion resistance post-testing. The synergistic effect of cyclic occlusal loading and bacteria biofilm could negatively affect the surface of titanium dental implants.

Corrosion Behavior of Boiler Tube under Circulation Water Conditions in District Heating System

In this study, corrosion behavior of a SA178-A alloy used in the boiler tube of a district heating system was investigated in different environments where it was exposed to pure water, district heating (DH) water, and filtered district heating (FDH) water. After the corrosion test, the surface morphology was examined for observation of the number of pitting sites and pitting area fraction, using a scanning electron microscope. The DH water and FDH water conditions resulted in a lower corrosion potential and pitting potential, and revealed a significantly higher corrosion rate than the pure water condition. The pitting sites in the DH water (pH 9.6) were approximately eighteen times larger than those in the pure water (pH 9.6). Compared to the DH water, the corrosion potential became more noble in the FDH water condition, where iron ions were reduced through filtration. However, the corrosion rate increased in the FDH water due to an increased concentration of chloride ions, which deteriorated the stability of passive film.

Effect of hot rolling on the corrosion behavior of AZ31 magnesium alloy

The aim of the present study is to investigate the effect of deformation conditions on the corrosion behavior of AZ31 (Mg-3Al-1Zn, % wt.) in 0.9% NaCl (wt.%) solution. The AZ31 alloy was hot rolled at 360 °C to 20 and 50% of thickness reduction. Electrochemical measurements were used to study the corrosion behavior of AZ31 alloy. Analysis of corrosion products after immersion test was performed using optical microscopy, X-ray diffraction and Raman spectroscopy. The mechanical properties of corroded samples were investigated using tensile test at room temperature. Results indicated that the corrosion rate was strongly affected by the hot rolling level. A lower corrosion potential and reduced polarization resistance was observed after hot rolling compared to the as received AZ31 alloy. The corrosion product was evidenced mainly as Mg(OH)2 compound exhibiting a filiform-like morphology. Apparently, the corrosion improved the room temperature ductility of AZ31 alloy.

Hydrogen generation from hydrolysis of activated magnesium/low-melting-point metals alloys

A series of activated Mg-based alloys with low-melting-point metals (Zn, Sn, Bi, and In) are prepared by ball milling and characterized by scanning electron microscope and X-ray diffraction. Their hydrogen generation properties are systematically investigated in seawater and methanol. The results demonstrate that the addition of low-melting-point metals can significantly accelerate the reaction of magnesium with seawater and methanol. The alloy Mg-10%In exhibits the excellent hydrolysis properties among all the samples with the maximum hydrogen generation rate of 7.4 mL g−1 s−1 and the hydrogen conversion yield of 93% at 30 °C in seawater. The excellent hydrolysis performance of Mg-10%In can be attributed to its lower activation energy, lower corrosion potential, and higher corrosion current density. Moreover, the active preservation method of activated Mg alloys by coating dioctyl sebacate is studied.

Corrosion Resistance of 2060 Aluminum⁻Lithium Alloy LBW Welds Filled with Al-5.6Cu Wire.

Alloy sheets of type 2060 aluminum–lithium were welded by laser beam welding (LBW) filled with ER2319 Al-5.6Cu wire. Microstructural observations showed the uneven distribution of columnar grains, equiaxed grains and equiaxed dendrite grains in the weld. The θ′(Al2Cu) phase and other phases precipitated in the weld. The θ′(Al2Cu) phase centrally distributed at the grain boundaries. During the immersion corrosion, the pitting corrosion first occurred and then gradually expanded and transformed to intergranular corrosion and exfoliation corrosion. The electrochemical corrosion test showed a higher corrosion tendency of the base metal and heat-affected zone for the lower corrosion potential, but the corrosion current density of the weld was relatively larger. The segregation of Cu, Mg and other elements at the grain boundary aggravated the occurrence of intergranular corrosion.

Nanosecond Laser Fabrication of Hydrophobic Stainless Steel Surfaces: The Impact on Microstructure and Corrosion Resistance.

Creation of hydrophobic and superhydrophobic surfaces has attracted broad attention as a promising solution for protection of metal surfaces from corrosive environments. This work investigates the capability of nanosecond fiber laser surface texturing followed by a low energy coating in the fabrication of hydrophobic 17-4 PH stainless steel surfaces as an alternative to the ultrashort lasers previously utilized for hydrophobic surfaces production. Laser texturing of the surface followed by applying the hydrophobic coating resulted in steady-state contact angles of up to 145°, while the non-textured coated base metal exhibited the contact angle of 121°. The microstructure and compositional analysis results confirmed that the laser texturing process neither affects the microstructure of the base metal nor causes elemental loss from the melted regions during the ultrafast melting process. However, the electrochemical measurements demonstrated that the water-repelling property of the surface did not contribute to the anticorrosion capability of the substrate. The resultant higher corrosion current density, lower corrosion potential, and higher corrosion rate of the laser textured surfaces were ascribed to the size of fabricated surface micro-grooves, which cannot retain the entrapped air inside the hierarchical structure when fully immersed in a corrosive medium, thus degrading the material’s corrosion performance.