Pitting Corrosion Potential Research Articles

Effects of Aging Precipitates on the Mechanical and Corrosion Resistance Properties of 18Cr-18Mn-2Mo-0.96N Super High Nitrogen Austenitic Stainless Steel

This paper investigates the effects of aging precipitates on the mechanical and corrosion resistance properties of 18Cr-18Mn-2Mo-0.96N super high nitrogen austenitic stainless steel (HNS) through Vickers hardness, Charpy impact, tensile and electrical chemical methods. The probable affected mechanism is discussed by optical microscope (OM) and transmission electron microscopy (TEM). The results are presented as follow: the initial TTP curve with 0.05% precipitates volume fraction presents C type which has a nose temperature at 850°C with an incubation period for 60s. The precipitates increase with prolonging aging time to 40%. The HV results of aged HNS present firstly decrease then increase, the relevant yield strength firstly increase then decrease with increasing the aging time. Meanwhile, the impact energy, ultimate tensile strength and elongation are deteriorated significantly because of the formation and growth of cellular Cr2N and χ phase with concomitant increased amount of intergranular Cr2N. The IGC susceptibility increases and the pitting corrosion potentials decrease because of the Cr, N and Mo depletion through the formation of intergranular, cellular Cr2N and intermetallic χ precipitates by aging treatments.

Preparation and characterization of mesoporous 45S5 bioactive glass–ceramic coatings on magnesium alloy for corrosion protection

To improve the bioactivity and corrosion resistance, mesoporous 45S5 bioactive glass–ceramic (45S5 MBGC) coatings were prepared on AZ31 magnesium alloy by the sol–gel dip-coating method and the evaporation-induced self-assembly (EISA) process. Non-mesoporous 45S5 bioactive glass–ceramic (45S5 BGC) coatings were also prepared for comparative investigation. The results showed that 45S5 MBGC coatings were prone to crack-free and uniform with larger special surface area, pore volume and better surface wettability in contrast to 45S5 BGC coatings. A possible mechanism of mesopore formation was proposed to better understand the role of Pluronic F127 (F127) in the preparation process. Furthermore, 45S5 MBGC coatings had desired adhesion strength to AZ31 substrate owing to chemical bonding interface. Electrochemical tests in simulated body fluid (SBF) revealed that 45S5 MBGC coatings could obviously improve the pitting corrosion potential and polarization resistance of AZ31 substrate, meanwhile, corrosion current density was significantly decreased, suggesting effective anti-corrosion property. Therefore, 45S5 MBGC coated magnesium alloys had potentials for use as biodegradable biomedical implant material.

Effect of Mo contents on corrosion behaviors of welded duplex stainless steel

The corrosion behaviour and change of the phase fraction in welded 24Cr Duplex stainless steel was investigated for different chemical composition ranges of Mo contents. Filler metal was produced by fixing the contents of Cr, Ni, N, and Mn while adjusting the Mo content to 0.5, 1.4, 2.5, 3.5 wt%. The δ-ferrite fraction was observed to increase as the content of Mo increased. A polarisation test conducted in a salt solution, indicated the pitting corrosion potential increased continuously to 3.5 wt% Mo, while the corrosion potential changed most between 0.5 and 1.41 wt% Mo. The location of the pitting corrosion in 0.5 wt% Mo steel was randomly distributed, but it occurred selectively at the grain boundary between the γ- and δ-ferrite phases in 1.4, 2.5 and 3.5 wt% Mo steel. Energy dispersive X-ray spectroscopy mapping analysis showed that areas deficient in Cr, Mo, and Ni occurred around the grain boundary of the γ- and δ-ferrite phases. Non-metallic inclusions are thought to act as initiation points for the pitting corrosion that occurs in the salt solution initially as a result of the potential difference between the matrix structure and the incoherent inclusions.

In vitro and in vivo studies on Ti-based bulk metallic glass as potential dental implant material

In this study, a high glass forming system, Ti41.5Zr2.5Hf5Cu37.5Ni7.5Si1Sn5 (TZHCNSS) bulk metallic glass (BMG), is studied in terms of microstructure, surface analysis, mechanical properties, corrosion resistance, in vitro cytotoxicity and in vivo biocompatibility. It is found that the as-prepared TZHCNSS samples are fully amorphous by XRD and TEM observations, as well as DSC curve. Comparing with pure Ti, TZHCNSS BMG shows superior mechanical properties with higher hardness and better wear resistance. Due to the oxide film formed on its surface, TZHCNSS BMG shows great corrosion resistance close to pure Ti in electrochemical measurements. The pitting corrosion potential in artificial saliva solution is much higher than that in SBF solution. The indirect and direct cytotoxicity results show that TZHCNSS extracts had obvious low cell viability on both L929 and NIH3T3 cells. However, the in vivo testing results proved that TZHCNSS BMG could integrate with bone tissue, showing excellent osseointegration.

INFLUENCE OF TEMPERATURE ON PITTING CORROSION RESISTANCE OF Cr26Mo1 ULTRA PURE HIGH CHROMIUM FERRITE STAINLESS STEEL IN 3.5%NaCl SOLUTION

通过循环极化曲线、Mott-Schottky曲线以及电化学阻抗谱等方法研究了温度对Cr26Mo1超纯高铬铁素体不锈钢在3.5%NaCl溶液中耐点蚀性能的影响.结果表明:随着温度升高,Cr26Mo1超纯高铬铁素体不锈钢的自腐蚀电位降低,腐蚀电流密度增大,点蚀电位下降,钝化膜阻抗降低.Cr26Mo1不锈钢钝化膜的半导体类型和性质在不同温度下发生改变.Cr26Mo1不锈钢发生点蚀的孕育期随着温度的升高而缩短,点蚀敏感性增加,已发生点蚀的试样不能够自修复.

The Inhibiting Effect of Monoethanolamine on 6063 Aluminum Alloy in Sodium Chloride Solution

Monoethanolamine (MEA) was investigated as corrosion inhibitors of a 6063 aluminum alloy in 3.5 % solution using polarization and electrochemical impedance spectroscopy techniques and weight loss. The polarization curves show that monoethanolamine (MEA) can increase corrosion potential (Ecorr) and pitting corrosion potential (Epit), and decrease corrosion current density (icorr) of the 6063 aluminum alloy. EIS results indicate that monoethanolamine (MEA) can increase impedance of the 6063 aluminum alloy. The results show that monoethanolamine exhibits better inhibitor properties for the 6063 aluminum alloy. Electrochemical test results show monoethanolamine (MEA) can improve corrosion resistance and the inhibition action depends on the concentration of the inhibitor. The weight-loss experiment also proves that monoethanolamine (MEA) can improve the corrosion resistance of the 6063 Al alloy.

Dissimilar Welding between AISI 304 Stainless Steel and AISI 1020 Carbon Steel Plates

Abstract. This work studied the feasibility of dissimilar welding between AISI 304 stainless steel and AISI 1020 carbon steel plates with the thickness of 15 mm. The processes applied in this work were gas tungsten arc welding (GTAW) and shield metal arc welding (SMAW). Microstructure of weld metal produced by GTAW consists of delta ferrite network in austenite matrix, while the dendrite of delta ferrite finely distributed in austenite matrix was found in the weld produced by SMAW. Hardness values of weld metals produced using these two techniques were superior to those of stainless steel and carbon steel base metals respectively. Weld metals produced by these two processes were qualified under tension and bending. This was justified by the result that the failed part after transverse tensile test was on carbon steel, and no crack was found in weld metal after U-shape bending. Impact test exhibited higher toughness of weld metal produced by GTAW than that produced by SMAW. This might be from microstructure of the former weld as network of delta ferrite in austenite matrix which might help absorb impact energy. Pitting corrosion potential of weld metal produced by GTAW was higher than that produced by SMAW and stainless steel base metal respectively. In the aspect of mechanical and corrosion properties of the weld, GTAW was considered as a promising process that could be used for dissimilar welding between these two metals.

Novel Cu-bearing economical 21Cr duplex stainless steels

A new family of 21Cr–2Ni–1.0Mo–0.2N–xCu (x=0.5,1.0,1.5) economical duplex stainless steels have been developed by examining the effect of Cu on the microstructure and properties of solution-treated specimens. The results have shown that these alloys have a balanced ferrite–austenite duplex structure. The ferrite content increases with the solution treatment temperature, but decreases with an increase in Cu. Some precipitates such as sigma phase, ε-Cu and Cr2N were found when solution-treated at 780°C for 30min. The yield strength, tensile strength and fracture elongation values of experimental alloys solution-treated at 1020°C for 30min were about 540MPa, 1000MPa, and 35%, respectively. The pitting corrosion potentials of the solution-treated alloys were all above 500mV in 1mol/L NaCl solution at room temperature and the pitting corrosions always occur in ferrite phase. The mechanical properties and corrosion resistance of the designed alloys with lower production cost are better than those of AISI 316L austenitic stainless steel.

Electrodeposition of aluminum–hafnium alloy from the Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt

The electrochemistry of Hf(IV) and the electrodeposition of Al–Hf alloys were examined in the Lewis acidic 66.7–33.3 mol% aluminum chloride-1-ethyl-3-methylimidazolium chloride molten salt containing HfCl4. When cyclic staircase voltammetry was carried out at a platinum disk electrode in this melt, the deposition and stripping waves for Al shifted to negative and positive potentials, respectively, suggesting that aluminum stripping is more difficult due to the formation of Al–Hf alloys. Al–Hf alloy electrodeposits containing ~13 at.% Hf were obtained on Cu rotating wire and cylinder electrodes. The Hf content in the Al–Hf alloy deposits depended on the HfCl4 concentration in the melt, the electrodeposition temperature, and the applied current density. The deposits were composed of dense crystals and were completely chloride-free. The chloride-induced pitting corrosion potential of the resulting Al–Hf alloys was approximately +0.30 V against pure aluminum when the Hf content was above 10 at.%.

Characterization of Passive Film Formed on AISI 316L Stainless Steel after Magnetoelectropolishing in a Broad Range of Polarization Parameters

AbstractThe aim of the paper is to present the changes in the surface film composition on AISI 316L stainless steel (SS) after electropolishing (EP) and magnetoelectropolishing (MEP) in a broad range of the process conditions. The X‐ray photoelectron spectroscopy surface analyses were performed to reveal the effect of MEP. The EP process has been performed under natural convection (in a stagnant electrolyte), much above the polarization plateau. A series of experiments were carried out on AISI 316L SS samples in accordance with the five‐level composite rotary statistical plan with the variables being the magnetic field intensity B (mT), and the anodic current density i (A dm−2). XP high resolution spectra have been obtained on AISI 316L SS surface concerning Fe 2p, Cr 2p, O 1s, S 2p, P 2p, and C 1s, respectively. The Cr:Fe ratio regarding both metallic M and compound X was also studied and calculated. At the end, the summary results of Cr/Fe = f(B, i) in relation to the corrosion potential, have been compared. The conclusions, concerning the selection of MEP process conditions, regarding the optimum Cr/Fe ratio and corrosion behavior, have been formulated. It was found the Cr:Fe ratio well correlates with the pitting corrosion potential. MEP process can modify not only the rate of dissolution to a determined extent, but also control the corrosion behavior and Cr:Fe ratio results.

Effect of Diethylamine Addition on the Sealing Process of 6063 Al Alloy

To improve the corrosion resistance of Al alloy, diethylamine (DEA) was added into the sealing solutions. The electrochemical behavior of sealing coatings formed in different concentrations of diethylamine (DEA) was investigated by means of polarization curves and electrochemical impedance spectroscopy (EIS). Compared with the coatings with D. I. water and the bare aluminum alloy, the polarization curves show that the sealing coatings formed in 3.0 – 5.0 ml.L-1 diethylamine (DEA) solutions have more positive corrosion potential (Ecorr) and pitting corrosion potential (Epit), and lower corrosion current density (icorr). Electrochemical parameters of EIS indicate that the sealing coatings have higher corrosion resistance. The electrochemical tests present that the prepared sealing coatings have better corrosion resistance.

Plasma Arc Welding between AISI 304 and AISI 201 Stainless Steels Using a Technique of Mixing Nitrogen in Shielding Gas

Plasma arc welding was applied to join AISI 304 and AISI 201 stainless steel sheets. Nitrogen was mixed in argon shielding gas to help control microstructure and improve corrosion property of the weld. It was found that increasing nitrogen in shielding gas from 0 to 12 %v/v reduced the amount of delta ferrite in austenite matrix of the weld from 20 to 16 %v/v. This indicated the role of nitrogen as an austenite stabiliser. From polarisation test in 3.5wt% NaCl solution at 25 °C, increasing nitrogen in shielding gas nobly shifted a pitting corrosion potential from 401 to 472 mV vs Ag/AgCl. This corresponded to the increase of nitrogen content in the weld from 0.11 to 0.19 wt%.

Influence of Triethylamine Inhibitor Addition on the Sealing Process of 6063 Al Alloy

To improve the corrosion resistance of Al alloy, triethylamine (TEN) was added into the sealing solutions. Tafel polarization and electrochemical impedance spectroscopy(EIS) techniques were used to investigate the electrochemical behavior of sealing coatings formed in different concentrations of triethylamine(TEN). Compared with the coatings with D. I. water and the bare aluminum alloy, the polarization curves show that the sealing coatings formed in 5.0 – 7 .0 g.L-1 triethylamine (TEN) solutions have more positive corrosion potential (Ecorr) and pitting corrosion potential (Epit), and lower corrosion current density (icorr). Electrochemical parameters of EIS indicate that the sealing coatings have higher corrosion resistance. The electrochemical test results show the prepared sealing coatings have better corrosion resistance.

Techniques for In Situ Corrosion Studies of 316L Stainless Steel in Sulfuric Acid Solutions

An in situ optical microscopy and simultaneous electrochemical analysis method is presented for studying 316L stainless steel in sulfuric acid based solutions. The electrochemical methods involved potentiostatic and potentiodynamic analysis of 316L stainless steel surface in aerated and deaerated 1M-3.39M H2SO4 while varying Ni+ and Cl-. This technique is reviewed along with several other in situ surface analytical probes and patents such as scanning tunneling microscopy (STM), scanning electrochemical microscopy (SECM) and variations on SECM (near fieldalternating current) and the results are discussed in conjunction with various theories and applications. The results when compared to SECM data indicate that the SECM resolution, control and performance are improved. The results also illustrate the wide variety of corrosion behaviors possible for 316L stainless steel under potentiostatic and potentiodynamic test conditions. Analysis of these samples provides both a detailed visual account of the corrosion process in addition to standard electrochemical analysis regarding pitting potentials, corrosion potential and corrosion rate. Polarization data and analysis regarding the corrosion patterns observed is presented including in situ images of etching, surface layer changes and pitting. Images and analysis of chromium carbide and sulfide inclusion behaviors in sulfuric acid were performed showing the tendency of inclusions to dissolve and act as nucleation sites for pits. Keywords: Aerated, dearated, etching, grain boundaries, inclusions, in situ, optical, pitting, potentiostatic, potentiodynamic, polarization, SEM-EDS, 316L, 1M-3.39M H2SO4

Corrosion performances in simulated body fluids and cytotoxicity evaluation of Fe-based bulk metallic glasses

The aim of this work is to investigate the corrosion resistance and biocompatibility of three kinds of Fe based bulk metallic glasses (BMGs), Fe41Co7Cr15Mo14C15B6Y2 (BMG1), (Fe44Cr5Co5Mo13Mn11C16B6)98Y2 (BMG2), and Fe48Cr15Mo14C15B6Er2 (BMG3) by electrochemical measurements and indirect contact cytotoxicity assays, respectively. In comparison with 316L SS biomedical steel, Fe based BMGs show better corrosion resistance in both simulated body fluids (Hank's solution and artificial saliva). The OCP curves show that the passive film on the Fe based BMG surfaces is quite stable, like 316L SS. The corrosion current densities obtained from the anodic polarization curves from the lowest to highest are as follows: BMG3<BMG1<BMG2<316L SS. The EIS analysis indicates that the Fe Based BMGs have larger polarization resistance value than that of 316L SS except for BMG2 in artificial saliva. The pitting corrosion potentials of Fe based BMGs are much higher than that of the 316L SS, resulting in very few ions releasing into the electrolytes while a significant amount of Ni and Fe ions release was found for 316L SS under the same condition. The indirect cytotoxicity results suggest that all three Fe based BMG extracts have no cytotoxicity to L929 and NIH3T3 cells. All these results demonstrate that Fe based BMGs will open up a new path for the biomedical applications, especially in dental implantology.

The Effect of Trace Boron Element on Local Corrosion Resistance of Casted 0.04C-16Cr Ferritic Stainless Steel

0.04C-16Cr and 0.04C-16Cr containing 26ppm B ferritic stainless steels were smelted by using a vacuum induction furnace. Then 65% boiling nitric acid method and the electrochemical potentiokinetic reactivation method (EPR) were used to research their intergranular corrosion sensitivity. Meanwhile, electrochemical test method (Tafel polarization curve method, the anode circular polarization curve method) and chemical immersion method were used to research their pitting corrosion resistance. The results showed that the corrosion rate of 0.04 C-16Cr stainless steel containing 26ppm B in 65% boiling nitric acid is lower than that of 0.04 C-16Cr stainless steel. The reactivation rate of 0.04C-16Cr containing 26ppm B in dilute sulphuric acid medium significantly reduced compared with that of 0.04C-16Cr. The pitting corrosion potential, self-corrosion potential and the value of (Eb-Ep) of the stainless steel containing with 26ppm B in chlorideions medium reduced, while the corrosion rate increased compared with the stainless steel without B addition. It indicates that trace boron addition improves the intergranular corrosion resistance and repair ability of the passive film of the 0.04C-16Cr ferritic stainless steel after pitting corrosion process in chloride ions medium, but it also promotes the pitting corrosion tendency of the steel. Besides, introduction B to 0.04C-16Cr ferritic stainless steel reduces the steel’s corrosion resistance in active dissolved zone and promotes its intergranular corrosion tendency in chloride ions medium. The electrochemical characteristics of local corrosion are consistent with the results of chemical immersion test.

Effect of Cu and Co Additions on Corrosion Behavior of NiTi Alloys for Orthodontic Applications

The aim of this study is to investigate effect of Cu and Co additions on corrosion behavior of NiTi shape memory alloys for orthodontic application. Ni50.6Ti49.4, Ti49Ni46Cu5 and Ti50Ni47Co3 (at%) alloys were prepared. The specimens were melted by arc-melting furnace and homogenized at 800oC for 3.6 ks. Transformation temperatures were analyzed by differential scanning calorimeter (DSC). The corrosion behavior was assessed electrochemically in artificial saliva (pH 5.35) at 37oC. Open circuit potential (OCP) was monitored 3.6 ks followed by potentiodynamic techniques. The results show that all of specimens revealed transformation temperature close to oral temperature which may be utilized as orthodontic wire. Surface roughness was measured in order to ensure that there is no significant difference which might affect corrosion resistance. It is seen that by adding Co and Cu into NiTi alloys, the corrosion potential (Ecorr) and pitting corrosion potential (Ebreak) increase resulting in lower corrosion rate. Conceivably, Co and Cu additions considerable affect the corrosion behavior of NiTi alloys by improving corrosion resistance in artificial saliva.

Enhanced in vitro biocompatibility of ultrafine-grained biomedical NiTi alloy with microporous surface

Bulk ultrafine-grained Ni 50.8Ti 49.2 alloy (UFG-NiTi) was successfully fabricated by equal-channel angular pressing (ECAP) technique in the present study, and to further improve its surface biocompatibility, surface modification techniques including sandblasting, acid etching and alkali treatment were employed to produce either irregularly roughened surface or microporous surface or hierarchical porous surface with bioactivity. The effect of the above surface treatments on the surface roughness, wettability, corrosion behavior, ion release, apatite forming ability and cytocompatibility of UFG-NiTi alloy were systematically investigated with the coarse-grained NiTi alloy as control. The pitting corrosion potential ( E pit) was increased from 393 mV (SCE) to 704 mV (SCE) with sandblasting and further increased to 1539 mV (SCE) with following acid etching in HF/HNO 3 solution. All the above surface treatment increased the apatite forming ability of UFG-NiTi in varying degrees when soaked them in simulated body fluid (SBF). Meanwhile, both sandblasting and acid etching could promote the cytocompatibility for osteoblasts: sandblasting enhanced cell attachment and acid etching increased cell proliferation. The different corrosion behavior, apatite forming ability and cellular response of UFG-NiTi after different surface modifications are attributed to the topography and wettability of the resulting surface oxide layer.

Enhanced corrosion resistance and cellular behavior of ultrafine-grained biomedical NiTi alloy with a novel SrO–SiO2–TiO2 sol–gel coating

NiTi alloy has a unique combination of mechanical properties, shape memory effects and superelastic behavior that makes it attractive for several biomedical applications. In recent years, concerns about its biocompatibility have been aroused due to the toxic or side effect of released nickel ions, which restricts its application as an implant material. Bulk ultrafine-grained Ni50.8Ti49.2 alloy (UFG NiTi) was successfully fabricated by equal-channel angular pressing (ECAP) technique in the present study. A homogeneous and smooth SrO–SiO2–TiO2 sol–gel coating without cracks was fabricated on its surface by dip-coating method with the aim of increasing its corrosion resistance and cytocompatibility. Electrochemical tests in simulated body fluid (SBF) showed that the pitting corrosion potential of UFG NiTi was increased from 393mV(SCE) to 1800mV(SCE) after coated with SrO–SiO2–TiO2 film and the corrosion current density decreased from 3.41μA/cm2 to 0.629μA/cm2. Meanwhile, the sol–gel coating significantly decreased the release of nickel ions of UFG NiTi when soaked in SBF. UFG NiTi with SrO–SiO2–TiO2 sol–gel coating exhibited enhanced osteoblast-like cells attachment, spreading and proliferation compared with UFG NiTi without coating and CG NiTi.

Corrosion Inhibition by Sorbitol/Diethylenetriamine Condensation Product for Carbon Steel in 3.5% NaCl Saturated Ca(OH)&lt;sub&gt;2&lt;/sub&gt; Solution

The inhibitive action of a sorbitol/diethylenetriamine condensation (SDC) product toward carbon steel corrosion in saturated Ca(OH)2 solution containing 3.5% NaCl was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), surface morphological observations, and quantum chemical calculations. The results indicate that the addition of SDC can effectively decrease the corrosion current densities of the carbon steel and increase the pitting corrosion potential suggesting that the local corrosion induced by Cl(superscript -) is strongly restricted by the inhibitor, which acts as a mixed type inhibitor. In the studied concentration range, the inhibition efficiency increased with an increase in inhibitor concentration. The overall inhibition behavior of SDC is attributed to the stabile adsorption film formd by the dominantly physical adsorption on the carbon steel surface according to the Langmuir adsorption isotherm.