Electrochemical corrosion behavior of arc sprayed Zn-Al coatings

Cored wires and high velocity arc spraying (HVAS) technique were applied to produce high Al content Zn-Al alloy coatings on low carbon steel substrates. The electrochemical corrosion behaviors of Zn, Al and Zn-Al coatings were studied with potentiodynamic measurement in 5 % NaCl solution. Compared with pure Zn, pure Al and Zn-15Al coatings, Zn-26Al coatings show a higher corrosion resistance in salt solution. The potentiodynamic polarization tests show that the corrosion resistance of Zn-Al coatings increases as Al content is raised. Pure Al coating exhibits different electrochemical behaviors with other coatings. The corrosion initiated at the micro-pores of the coating and the underlying corrosion mechanism is very similar to that of the pitting corrosion.

ELECTROCHEMICAL NOISE FEATURES OF PURE ALUMINUM DURING PITTING CORROSION IN NEUTRAL NaCl SOLUTION

Spontaneous electrochemical noise (EN) can be a rich source of information concerning the processes simultaneously occurring at a corroding interface. Potential noise fluctuations during the free corrosion of pure aluminum in different concentration of neutral sodium chloride solution are investigated, and the breakdown and restoration of passive metal's film are studied using potentiodynamic scanning (PDS) measurements and electrochemical impedance spectroscopy (EIS) technique. Two capacitance loops are observed in the Nyquist plots in two kinds of concentration, and the corrosion process is under activation control at first, then become diffusion control within the oxide film and corrosion products of (Al(OH)p-mCl-m) accumulated on the surface of the corroding electrode. It is suggested that the pitting corrosion is much easier to occur for pure aluminum in 7.0wt% than in 2.0wt% NaCl solution, and the high concentration of chloride ion in solution inhibits the repassivation of a metastable pit. The corrosion rate deterministic step does not involve Cl-.

ELECTROCHEMICAL FEATURES DURING PITTING CORROSION OF LY12 ALUMINUM ALLOY IN DIFFERENT NEUTRAL SOLUTIONS

The electrochemical features of commercial airfrarne material, Al alloy LY12, in 0.349mol/L neutral sodium chloride (NaCl) and sodium sulfate (NazSO^) solutions were investigated by electrochemical impedance spectroscopy (EIS) and potentiody-namic polarization techniques. The microstructure of the as-tested samples was studied by scanning electron microscopy. The results show that the Nyquist plots of LY12 at different immersion time displayed different features, indicating that the Cl- ions elevate the corrosion rate and inhibit the repassivation of a metastable pit. It also shows that the corrosion product of LY12 formed in SO42- solution isn't easy to dissolve, and it will cover the surface of working electrode in the electrolyte. SEM images indicate that the corrosion apparent area and pit number of LY12 in NaCl solution are greater than that in Na2SO4 solution.

Galvanic corrosion behavior of plain carbon steel-B_4C composite in 3.5% NaCl solution with electrochemical noise

The galvanic corrosion behavior of metal-matrix composite plain carbon steel/boron carbide(B_4C) in 3.5%NaCl solution was studied.The composite was locally produced as a weld band on carbon steel by means of the gas tungsten arc welding process and using nickel as the wetting agent.Samples from the weld band,heat-affected zone and parent metal region were extracted precisely and DC/AC electrochemical tests in combination with techniques such as scanning electron microcopy and energy dispersive spectrometry were conducted.The results of the electrochemical tests show that the corrosion resistance of the parent metal sample is higher than that of the welded composite and the HAZ samples.However,as the corrosion potential(E_(Corr)) of the parent metal is more positive than other two samples,this becomes the cathode in galvanic couples with two other samples.On the other hand,the weld composite sample is also cathodic due to its more positive E_(Corr) compared to HAZ sample.This means that the HAZ can be particularly at risk of preferential dissolution.The approach can be used in specific areas on plain carbon steel to locally increase hardness and resistance to abrasion and reduce manufacturing costs.

Effect of thermomechanical cyclic quenching and tempering treatments on microstructure,mechanical and electrochemical properties of AISI 1345 steel

Thermomechanical cyclic quenching and tempering(TMCT)can strengthen steels through a grain size reduction mechanism.The effect of TMCT on microstructure,mechanical,and electrochemical properties of AISI 1345 steel was investigated.Steel samples heated to 1050℃,rolled,quenched to room temperature,and subjected to various cyclic quenching and tempering heat treatments were named TMCT-1,TMCT-2,and TMCT-3 samples,respectively.Microstructure analysis revealed that microstructures of all the treated samples contained packets and blocks of well-refined lath-shaped martensite and retained austenite phases with varying grain sizes(2.8–7.9μm).Among all the tested samples,TMCT-3 sample offered an optimum combination of properties by showing an improvement of 40%in tensile strength and reduced 34%elongation compared with the non-treated sample.Nanoindentation results were in good agreement with mechanical tests as the TMCT-3 sample exhibited a 51%improvement in indentation hardness with almost identical reduced elastic modulus compared with the non-treated sample.The electrochemical properties were analyzed in 0.1 M NaHCO_(3) solution by potentiodynamic polarization and electrochemical impedance spectroscopy.As a result of TMCT,the minimum corrosion rate was 0.272 mm/a,which was twenty times less than that of the nontreated sample.The impedance results showed the barrier film mechanism,which was confirmed by the polarization results as the current density decreased.

Electrochemical performance of organic film on copper surface by polymer plating of 6-mercapto-1,3,5-triazine-2,4-dithiol monosodium

The 6-mercapto-1,3,5-triazine-2,4-dithiol monosodium(TTN) compound was used to fabricate an organic film on pure copper. The polymer plating process of TTN on pure copper in Na2CO3 aqueous solution and the growth mechanism of poly(6-mercapto-1,3,5-triazine-2,4-dithiol)(PTT) film were studied by means of cyclic voltammetry. The polymer plating under galvanostatic mode at 0.05 mA/cm2 was conducted to generate PTT film on pure copper in the same electrolyte with different polymer-plating time. The film mass was determined by electronic balance and the insoluble fraction in tetrahydrofuran(THF) Is tested. The performance of organic film formed on copper surface was investigated preliminarily by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS). It is found that a slight peak measured at 0 V vs SCE attributes to the oxidation of copper and generated Cu+ or/and Cu2+ to produce Cu-TTN complex,then a strong oxide peak is observed at 0.311 V vs SCE due to the polymerization of TTN for the increase of the film thickness. Electrochemical measurement results reveal that 10 min is an optimum polymer-plated time to obtain high quality film. The results of potentiodynamic polarization show that current density decreases from 1.85 μA/cm2 for bare copper to 0.168 μA/cm2 for polymer-plated copper while polymer-plated time is 10 min. The charge transfer resistances of bare copper and polymer-plated copper are 937 Ω·cm2 and 11.12 kΩ·cm2,respectively. The film capacitor for polymer-plated copper is as low as 1.82 μF·cm2. The EIS results confirm the results of potentiodynamic polarization and reveal that a homogenous and compact film is obtained by polymer plating technique.

Microstructure characterization and electrochemical corrosion behavior of Zn and Zn/Mg alloys in H_2SO_4 solution

The three systems of pure Zn, Zn-0.10% Mg(mass fraction), and Zn-0.15% Mg(mass fraction) were cast under controlled atmosphere and their microstructures were characterized by SEM/EDS analysis. The electrochemical corrosion behavior of these three samples was examined in the very aggressive solution of 50% H2SO4(mass fraction) using electrochemical impedance spectroscopy(EIS) and potentiodynamic polarization measurements. The results show that magnesium improves in some extent the corrosion resistance of pure Zn in 50% H2SO4(mass fraction) confirmed by EIS test. Results of polarization measurment also demonstrate that small amount of Mg significantly improves the passivation of Zn in the test solution. Results of surface morphology of the samples and EDS analysis reveal that Mg reduced the corrosion attacks to pure Zn.

不锈钢供水管材的土壤外腐蚀特性试验

试验以砖红壤中Cl^(-)和含水率为研究要素,借助电化学工作站,开展3种不锈钢供水管材(304、304L、316L)外腐蚀试验。结果表明:3种不锈钢在不同Clˉ和含水率的砖红壤中均有不同程度腐蚀倾向(304>304L>316L);当砖红壤Clˉ质量分数在10~1 250 mg/kg时,3种不锈钢腐蚀电流增幅(ΔI_(corr低))较大,为304L>316L>304,当Cl_(ˉ)质量分数在1 250~2 500 mg/kg时,其Δ_(Icorr高)较小,为304L>304>316L,即腐蚀减缓,Clˉ在一定范围内促进不锈钢管材腐蚀。与此同时,当砖红壤含水率在5%~35%时,3种不锈钢ΔI_(corr)为304L>316L>304,其中,当含水率在15%~25%时,其ΔI_(corr中)较大,为304L>316L>304,即腐蚀加快,含水率在一定范围内使不锈钢管材腐蚀加快。

化学氧化法制备表层含CuO的超细铜线及其电化学腐蚀行为研究

采用化学氧化法在超细铜线表面制备氧化物CuO,研究了不同溶液配比和反应时间制备的样品的物相成分、表面微观形貌,并通过动电位极化曲线(PD)、电化学阻抗谱分析(EIS)探究其电化学腐蚀行为。结果表明,当氢氧化钠与过硫酸铵溶液配比为1∶1,反应时间1.0 h,经过1.0 h热烧结后得到的样品表层物质为CuO/Cu_(2)O,表面微观形貌呈碎片状,具有良好的耐腐蚀性能。原因主要是由于铜表面氧化膜的形成抑制了腐蚀反应,有效阻止了腐蚀性离子在界面的传递和扩散。

GCr15轴承钢在电化学-机械加工中的电化学特性

GCr15轴承钢的高硬度特性造成其加工过程中刀具磨损快、加工品质不稳定等问题。电化学-机械加工方法在加工高硬度且能导电的材料方面具有独特优势。采用极化曲线法、电化学阻抗谱和莫特−肖特基曲线测试,考察了GCr15轴承钢在NaCl、NaClO_(3)和NaNO_(3)三种电解质溶液中的自腐蚀电位,以及电解质的类型与浓度对GCr15轴承钢电化学特性的影响。结果表明:GCr15轴承钢在NaCl电解液中不存在钝化区,在NaNO_(3)和NaClO_(3)电解液中存在稳定的钝化区,而质量分数为20%的NaNO_(3)电解液更有利于形成稳定的钝化区。在稳态钝化电位区间内形成的钝化膜的厚度和阻抗因钝化电位不同而不同,如何使其更有利于材料的电化学-机械加工有待进一步研究。

Corrosion Behaviour of Zr-Ag Alloys for Dental Implant Application

The electrochemical corrosion behaviour of three Zr-Ag alloys (Zr-1Ag, Zr-3Ag and Zr-5Ag) was investigated. Open circuit potential, linear potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were employed in aerated artificial saliva (pH = 4.0) at 37°C. Silver alloying additions are found to be effective in enhancing the corrosion resistance of zirconium in artificial saliva environment. In fact, Zr-Ag alloys exhibit higher open circuit potentials, larger breakdown potentials and higher impedance values as compared to cp Zr. This behaviour can be ascribed to the formation of a thicker and more stable passive film with increasing compactness, able to provide better protection against the corrosion attack.

NaCl溶液中Al-Li合金腐蚀过程的电化学特征

采用电化学噪声技术,结合电化学阻抗谱及极化曲线测量,研究了峰时效AA2195-T8铝合金在3.0％NaCl溶液中的腐蚀电化学特征.结果表明,腐蚀初期,合金表面钝化膜上不断有孔核的形成与修复,并导致阻抗谱上感抗成分的存在.随腐蚀时间的延长,其感抗成分消失且阻抗模值降低.阳极极化时,由于其孔蚀电位与自腐蚀电位接近,钝化电位区间很小;随腐蚀时间的延长,极化电阻先增加而后减小,自腐蚀电流则呈相反趋势变化.

Zn-Al系列高速电弧喷涂层电化学防腐性能研究

采用粉芯丝材和高速电弧喷涂技术制备高Al 含量的 Zn 26 %Al 涂层。通过电化学的方法测试涂层在5 %NaCl溶液下的腐蚀行为,并与由实芯丝材纯 Zn、纯 Al 及 Zn 15 %Al 所制备的涂层作比较。结果表明:Zn 26 %Al 涂层在电解质溶液中表现出更优越的防腐性能。动电位极化测试结果说明 Zn Al 涂层随着 Al 含量的增加,其耐蚀性也提高。纯 Al 涂层的电化学腐蚀行为与其它涂层有明显差异,其腐蚀机理类似于点蚀。

铁素体不锈钢的晶间腐蚀性能研究

分别采用Cu-CuSO4-16%H2SO4沸腾试验和电化学再活化方法研究了八种400系列铁素体不锈钢的晶间腐蚀性能.结果表明:C含量及稳定化元素是影响铁素体不锈钢晶间腐蚀性能的关键因素;电化学测量方法评价铁素体不锈钢的晶间腐蚀性能时易受晶粒再活化的影响,可结合电镜观察表面提高测量的准确性.

温度对Ni-金刚石复合电沉积电化学行为的影响

在测定Ni-金刚石复合电沉积体系阴极极化曲线、电化学阻抗谱及微分电容曲线等基础上,分析了温度对界面双电层的影响规律,推断出金刚石微粒复合量随温度升高的变化趋势,以此探讨温度在Ni-金刚石复合电沉积中的电化学行为。结果表明:随镀液温度沿30℃→40℃→60℃升高,Ni-金刚石复合体系的阴极极化减小,法拉第电阻沿17.3?→5.2?→3.0?降低,双电层电容沿40.8μF→141.2μF→175.6μF增加,同时,阴极表面在析出电位附近的负电荷密度逐渐增加。电化学测试结果表明:金刚石微粒复合量将随温度的升高而降低,且工艺实验与电化学测试结果也映证这一点。

表面粗糙度对硝酸钝化304不锈钢点蚀行为影响

采用动电位扫描、电化学阻抗谱和电化学噪声等方法研究了不同表面粗糙度的304不锈钢在体积分数10%HNO3溶液中钝化后的耐蚀性。结果表明,随304不锈钢钝化前表面粗糙度从0.25μm降到0.10μm,电荷转移电阻从6.51kΩ·cm2上升到19.17kΩ·cm2,电位标准偏差和电流标准偏差降低,而噪声电阻增大;随表面粗糙度的增大,试样电位和电流的功率密度曲线线性部分的斜率均出现增大,谱噪声曲线线性部分的斜率下降,表明在光滑的不锈钢表面更容易形成致密稳定且耐腐蚀性强的氧化膜,硝酸钝化能显著改善304不锈钢耐点蚀性能。

904L不锈钢在5g/L H_2SO_4溶液中的腐蚀行为

为了研究904L不锈钢在5 g/L H2SO4溶液中的腐蚀行为,采用动电位极化测试、电化学阻抗测试(EIS)和X射线光电子能谱(XPS)研究其腐蚀行为,并分析其钝化膜的组成.结果表明,904L不锈钢极化后会发生自钝化,钝化区间为-0.2~0.6 V,电荷传递电阻为4 801Ω/cm2,表明904L不锈钢具有较强的耐蚀性能.X射线光电子能谱(XPS)研究表明,钝化膜主要成分为Cr2O3、Cr OOH、Cr(OH)3等化合物.因而904L不锈钢在5 g/L H2SO4溶液中可以表现出良好的耐蚀性能.

几种缓蚀剂在3.5%NaCl溶液中对A3钢的缓蚀性能

采用动电位极化曲线、交流阻抗和扫描电镜法研究了乙二胺四乙酸二钠、二乙胺基乙醇、葡萄糖酸钙、磷酸氢二钠在3.5%NaCl溶液中对A3碳钢的缓蚀作用。研究结果表明,四种缓蚀剂均为阳极型缓蚀剂,缓蚀效果为:磷酸氢二钠>乙二胺四乙酸二钠>葡萄糖酸钙>二乙胺基乙醇。

表面状态对X80管线钢腐蚀行为的影响

采用线性极化测试、电化学阻抗谱和动电位极化等电化学测试技术并结合表面分析方法,研究了表面状态对X80管线钢在模拟土壤溶液(NS4)中的腐蚀行为影响。试验结果表明,随着表面粗糙度下降,其自然腐蚀电位向正向移动,腐蚀电流密度下降,即腐蚀速率减小;不同粗糙度的X80钢试样在NS4溶液中电化学阻抗谱表现为一个时间常数;随表面粗糙度的逐渐减小,电荷转移、电阻逐渐增大。微观形貌显示,试样表面腐蚀产物随着粗糙度的减小而逐渐减少。试样表面效应是引起不同粗糙度钢腐蚀差异的重要因素。