钢铁点蚀坑内腐蚀产物对点蚀扩展的影响

为了探讨钢铁点蚀坑内部生成的腐蚀产物对点蚀生长的影响,使用自制的2种铁微电极,通过电化学三电极体系,使之在阳极极化条件下发生溶解,一定程度上模拟点蚀生长的特征。结果表明:采用微型注射器可以将2种铁微电极表面黑色腐蚀产物沉积层冲洗到模拟点蚀坑外部,消除其对点蚀扩展的影响;通过对比冲洗前后的阳极溶解电流随时间的变化趋势,可以计算该腐蚀产物对模拟点蚀生长速率的影响;借助2种铁微电极的特殊性,提出了对其点蚀内部腐蚀产物影响进行量化的方法,将其用于修正点蚀内部金属离子的扩散系数,在一定程度上可完善点蚀的生长和预测模型。

核电站主泵的主轴、堆焊层和护环材料的抗腐蚀性能分析

本文阐述压水堆一回路主泵(冷却剂循环泵)的主轴、堆焊层和护环材料的试验研究,分析它们在常温下的点蚀行为和电偶腐蚀行为,在高温高压环境中的均匀腐蚀和应力腐蚀行为。分析结果表明,主轴、堆焊层和护环材料具有较好的抗点蚀能力,在发生点蚀后其膜具有自修复能力,能阻止点蚀的进一步发展;主轴-堆焊层电偶对、堆焊层-护环电偶对发生电偶腐蚀的电流密度分别为0.129μA/cm^2、0.039μA/cm^2,属于电偶腐蚀敏感性评价等级中的A级,两种电偶对具有很好的耐电偶腐蚀性能;主轴-堆焊层-护环焊接接头在300℃的高温水中腐蚀3000 h后,没有发生应力腐蚀,且均匀腐蚀速率仅为0.23 mg/dm^2·m。分析结果对主泵的主轴、堆焊层和护环的设计和选材具有重要指导意义。

Ti_(41.4)Zr_(28.5)Cu_(6.4)Nb_(8)Be_(15.6)非晶复合材料不同状态下的腐蚀行为对比

为确定非晶复合材料在不同状态下的腐蚀情况,以Ti_(41.4)Zr_(28.5)Cu_(6.4)Nb_(8)Be_(15.6)的合金锭、棒材和棒材在空气中放置15 d后的样品为材料,在NaCl溶液为腐蚀介质的模拟海水环境中,进行了电化学腐蚀测试以及化学浸泡试验。结果表明:铜模吸铸制备的棒材样品由于成型过程中冷却速率更快,结构更加均匀,其耐腐蚀性能明显优于熔炼为合金锭的样品。电化学测试后,其腐蚀电流密度达到2.7×10^(-8)A·cm^(-2)。同时,表面氧化处理后,由于表面氧化膜的存在,棒材Ti基非晶复合材料的耐腐蚀性能得到一定程度的提高。

高温炉水中Cl^-对碳钢水冷壁管的腐蚀行为研究

通过高压釜静态试验及表面膜EPMA分析 ,得出在高温炉水中 ,2 0A碳钢的增重速率随Cl- 浓度升高而提高 ,在 0 .4mg/L时达到最大值 ,然后又逐渐降低 ;其溶解速率呈对数曲线变化 ;Cl- 在开口蚀孔周围富集 ,含量高于蚀坑内 ,对现场水冷壁管取样分析也得到了相同的结论。

姿控发动机内舱壳体腐蚀机理分析

采用宏观形貌观察、化学成分分析、金相组织观察、扫描电子显微镜等方法对秦岭山区姿控发动机内舱壳体腐蚀进行了分析。结果表明:发动机内舱壳体的腐蚀是由于电化学腐蚀造成的,并且与秦岭山区特殊的外界环境有关,提出了相应的改进建议。

温度对API—X60管线钢HeS／CO2腐蚀行为的影响

利用高温高压反应釜模拟高含硫气田H2S／CO2共存环境，在流动溶液介质中进行腐蚀试验，辅以扫描电子显微镜和X射线衍射仪等研究手段，探讨了温度对API—X60管线钢H2S／CO2腐蚀行为的影响。结果表明，随着温度的升高，API-X60管线钢的腐蚀速率先升高后降低，腐蚀形态由局部腐蚀趋于全面腐蚀，高温区有点蚀倾向。低温时形成的腐蚀产物以马基诺矿型晶体和铁的单硫化物为主，随着温度的升高，腐蚀产物以层片状马基诺矿型晶体为主，并出现少量磁黄铁矿型晶体，高温区则以磁黄铁矿型晶体为主。低温区点蚀的发生是由于腐蚀产物附着力差导致其覆盖率降低，膜层覆盖处的阴极效应促进了局部腐蚀。

Corrosion and electrochemical behavior of Mg-Y alloys in 3.5% NaCl solution

The corrosion mechanism of Mg-Y alloys in 3.5% NaCl solution was investigated by electrochemical testing and SEM observation. The electrochemical results indicated that the corrosion potential of Mg-Y alloys in 3.5% NaCl solution increased with the increase of Y addition. The corrosion rate increased with the increase of Y addition because of the increase of Mg24Y5 intermetallic amounts. The corrosion gradually deteriorated with the increase of immersion time. The corrosion morphologies of the alloys were general corrosion for Mg-0.25Y and pitting corrosion for Mg-8Y and Mg-15Y, respectively. The main solid corrosion products were Mg（OH）2 and Mg2（OH）3C1·4H2O.

Effect of pretreatment on electrochemical etching behavior of Al foil in HCl-H_2SO_4

The aluminum foil for high voltage aluminum electrolytic capacitor was immersed in 0.5 mol/L H3PO4 or 0.125 mol/L NaOH solution at 40 ℃ for different time and then DC electro-etched in 1 mol/L HC1＋2.5 mol/L H2SO4 electrolyte at 80 ℃. The pitting potential and self corrosion potential of A1 foil were measured with polarization curves （PC）. The potentiostatic current--time curve was recorded and the surface and cross section images of etched A1 foil were observed with SEM. The electrochemical impedance spectroscopy （EIS） of etched A1 foil and potential transient curves （PTC） during initial etching stage were measured. The results show the chemical pretreatments can activate A1 foil surface, facilitate the absorption, diffusion and migration of C1- onto the A1 foil during etching, and improve the initiation rate of meta-stable pits and density of stable pits and tunnels, leading to much increase in the real surface area and special capacitance of etched A1 foil.

Electrochemical corrosion properties of Zr- and Ti-based bulk metallic glasses

The corrosion behaviors of Ti-based and Zr-based amorphous alloys and their corresponding crystallized alloys were studied by electrochemical methods. It is found that the corrosion potentials of Zr-based amorphous alloy and its corresponding crystalline counterpart are both lower than those of the Ti-based amorphous alloy in the 1 mol/L H2SO4 solution. In the 3.5% NaCl solution,Zr-based crystallized alloy exhibits the lowest corrosion potential among the experimental samples. No passivation is observed in the corrosion process for the Zr-based crystalline alloy. However, Zr- and Ti-based amorphous alloys both exhibit passivation characteristics. EIS measurements indicate the amorphous alloys exhibit better corrosion resistance than the crystallized one in the NaCl solution. Surface analysis shows that both amorphous alloys in the NaCl solution are eroded by pitting corrosion. In the H2SO4 solution, all the alloys display similar behaviors and their surfaces can mostly keep intact except for some cracks on the corroded surface at local region.

Influence of thermomechanical treatments on localized corrosion susceptibility and propagation mechanism of AA2099 Al-Li alloy

In order to manifest the influence of specific microstructural component on the development of severe localized corrosion in an AA2099 aluminum-lithium alloy, the corrosion behavior of the alloy subjected to solution heat treatment, cold working and artificial ageing was investigated. Immersion testing and potentiodynamic polarization were employed to introduce localized corrosion; scanning electron microscopy and transmission electron microscopy were used to characterize the alloy microstructure and corrosion morphology. It was found that the susceptibility of the alloy to severe localized corrosion was sensitive to thermomechanical treatments. Additionally, the state of alloying elements influenced the mechanism of localized corrosion propagation. Specifically, the alloy in T8 conditions showed higher susceptibility to severe localized corrosion than that in other conditions. During potentiodynamic polarization, the alloy in solution heat-treated and T3 conditions displayed crystallographic corrosion morphology while the alloy in T6 and T8 conditions exhibited selective attack of grain interiors and grain boundaries in local regions.

Effect of chemical plating Zn on DC-etching behavior of Al foil in HCl-H_2SO_4

The Al foil for high voltage Al electrolytic capacitor usage was immersed in 5.0%NaOH solution containing trace amount of Zn2＋and Zn was chemically plated on its surface through an immersion-reduction reaction. Such Zn-deposited Al foil was quickly transferred into HCl-H 2 SO 4 solution for DC-etching. The effects of Zn impurity on the surface and cross-section etching morphologies and electrochemical behavior of Al foil were investigated by SEM, polarization curve （PC） and electrochemical impedance spectroscopy （EIS）. The special capacitance of 100 V formation voltage of etched foil was measured. The results show that the chemical plating Zn on Al substrate in alkali solution can reduce the pitting corrosion resistance, enhance the pitting current density and improve the density and uniform distribution of pits and tunnels due to formation of the micro Zn-Al galvanic local cells. The special capacitance of etched foil grows with the increase of Zn2＋concentration.

敏化温度对SAF2304双相不锈钢耐局部腐蚀性能的影响

用双环电化学动电位再活化法(DL EPR)和临界点蚀温度(CPT)分别评价了在不同温度(600—950℃)下敏化处理2 h对SAF2304双相不锈钢的耐晶间腐蚀性能和耐点蚀性能的影响、并通过电化学蚀刻技术结合SEM对材料的微观组织演变进行了表征.结果表明,随着敏化温度的升高,SAF2304双相不锈钢的耐晶间腐蚀性能和耐点蚀性能都是先变差后增强,在700和750℃下敏化处理2 h后其耐局部腐蚀性能最差.对材料微观组织形貌的表征显示,Cr_2N的析出及其周边贫Cr区的形成是导致材料耐蚀性能下降的主要原因.

Corrosion and pitting behavior of pure aluminum 1060 exposed to Nansha Islands tropical marine atmosphere

The corrosion and pitting behavior of pure aluminum 1060 exposed to Nansha Islands marine atmosphere for 34 months was investigated based on mass loss measurement,scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS),and electrochemical impedance spectroscopy(EIS).The results indicated that serious pitting corrosion occurred on the surfaces of pure aluminum.The corrosion rate after exposure for 13 months was approximately 1.28 g/(m^(2)·a).The XPS results showed that the corrosion products were Al_(2)O_(3),Al(OH)_(3),and AlCl_(3).Moreover,the corrosion product layer was more protective than the native oxide film,and the protectiveness first increased and then decreased.Finally,the shape of the pits was evaluated using statistical analysis.

Probabilistic Assessment of Pitting Corrosion Effect on Flexural Strength of Partial Prestressed Concrete Structures in a Chloride Environment

Like reinforced concrete （RC） structure, Prestressed concrete （PC） structures cannot escape from corrosion related problems, especially when they are subjected to very aggressive environment, such as chloride environment. The corrosion of PC and RC structures can take place if the concrete quality is not adequate, the concrete cover is less than that specified in the design, poor detailing during design and construction. For RC structures, corrosion in the reinforcing steel generally leads to serviceability problems （staining, cracking and spalling of concrete）. By contrast, for PC structures, corrosion of prestressing strands may initiate structural collapse due to higher stress levels in the steel and smaller diameter of the prestressing steel. Research on corrosion effect on concrete structure has mainly considered the effect of corrosion have on reinforced and full prestressed concrete structure. In this study, a structural framework will be developed to predict the flexural strength of partial prestressed concrete structures in a chloride environment. The corrosion model previously developed for reinforced and prestressed concrete structures will be combined to predict the effect of corrosion has on partial prestressed concrete structures. Note that in partial prestressed concrete structures, both non prestressing steel （passive） and prestressing （active） reinforcement are utilized to carry the load. The framework developed will be combined with probability analysis to take into account the variability of parameters influencing the corrosion process. This approach allows more accurate prediction of service life of partial prestressed concrete structures in a chloride environment.

H_2S Stress Corrosion Tests of Welded Joint for X65 Pipeline Steel and Finite Element Numerical Analysis of Crack Tip

The microstructure of welded joint is surveyed and the mechanical properties of X65 pipeline steel are studied in this paper, which provides experimental basis of performance effect on stress corrosion. H 2S stress corrosion cracking (SCC) tests on the steel are carried out in the environment based on NACE TM- 01-77 solution. The threshold stress intensity factor and crack propagation velocity for base metal and HAZ are obtained. The susceptibility of welded joint for X65 pipeline steel to H 2S stress corrosion cracking is investigated. The programming package ANSYS of finite element model (FEM) is used to perform the three-dimensional elastic-plastic finite element analysis of WOL specimens. Stress field and concentration of hydrogen distribution property of the crack tip are obtained.

Corrosion behavior of B10 copper-nickel alloy beneath a deposit caused by sulfate-reducing bacteria with carbon source starvation in marine environments

Copper-nickel alloys can suffer severe localized corrosion in marine environments containing sulfate-reducing bacteria(SRB),but the effect of SRB on the under-deposit corrosion of copper-nickel alloys is unknown.In this work,the corrosion behavior of B10 copper-nickel alloy beneath a deposit caused by SRB with carbon source starvation in artificial seawater was studied based on electrochemical measurements and surface analysis.Results demonstrate that SRB with an organic carbon starvation can survive in artificial water but most SRB cells have died.The survived SRB cells can attach to the bare and deposit-covered B10 copper-nickel alloy,leading to the corrosion acceleration.Due to the limitation of organic carbon source,the pitting corrosion of B10 copper-nickel alloy caused by SRB is not serious.However,serious pitting corrosion of the deposit-covered B10 copper-nickel alloy can be found both in abiotic and biotic conditions,and the pitting corrosion and uniform corrosion are further accelerated by SRB.There is a galvanic effect between the bare and deposit-covered specimens in the presence of SRB in the early stage but the galvanic effect after 5 d of testing can be neglected due to the low OCP difference values.

某核电高压加热器传热管缺陷问题分析与处理

高压给水加热器是核电站二回路重要设备,就某核电机组首次大修高加传热管涡流检测发现大量缺陷问题,分别用缺陷机理矩阵分析法和故障树分析法对传热管缺陷原因进行了分析,得出传热管缺陷原因为点蚀腐蚀;并对缺陷传热管堵管准则进行了论述,分析了大比例堵管对机组热力性能的影响,总结了开展长周期检查策略等手段持续监督该加热器传热管完整性的建议。