304奥氏体不锈钢在酸性氯离子溶液中应力腐蚀性能的研究

采用慢应变速率拉伸实验研究了304奥氏体不锈钢在60℃时,不同氢离子浓度的NaCl溶液中的应力腐蚀性能。实验结果表明,随着氢离子浓度的增大,304不锈钢的应力腐蚀敏感性增强,但是当氢离子浓度达到一定程度时,应力腐蚀敏感性显著下降,这是由于当氢离子浓度过大时,均匀腐蚀的作用优先于应力腐蚀作用成为主导。在这种阳极溶解型应力腐蚀开裂中,氢和应力的交互作用增加了304不锈钢在酸性氯离子溶液中的应力腐蚀敏感性。     

用小冲杆试验法评估304L不锈钢的应力腐蚀敏感性

利用小冲杆试验对304L不锈钢进行了应力腐蚀敏感性评估,研究了加载速度和腐蚀介质对评估结果的影响,并对小冲杆试样的断口形貌和显微组织进行了分析。结果表明:最适合304L不锈钢评估的小冲杆应力腐蚀试验介质为1.0mol.L-1 NaCl+0.5mol.L-1 HCl混合溶液,加载速度为3×10-3 mm.min-1;在以上介质中,304L不锈钢小冲杆试样断口以穿晶解理断裂为主,部分为准解理断裂;小冲杆试验法是一种有效的应力腐蚀敏感性评估手段,且具有快速近乎无损等特点。     

304不锈钢表面Cr-N涂层耐腐蚀性能分析

基于动态电位极化腐蚀测试结果,在通入H2和O2的环境中,腐蚀电阻大小分别是C r2N304不锈钢裸片和304不锈钢裸片C r2N。静态电位极化腐蚀测试显示在模拟阳极条件中,304不锈钢(C r2N涂层)展现了比304不锈钢裸片低的极化电流密度,但是随着时间增长,电流密度变高了,因为腐蚀已经在微孔洞区域开始了。在模拟阴极环境中,由于在微孔洞区域的不锈钢基底已经发生钝化,因此提供了高的腐蚀保护,在涂层中的微孔洞的负面影响变小了。     

35CrMo钢在酸性H_2S环境中的应力腐蚀行为与机理

通过模拟油田井下低浓度H2S的工作环境,采用电化学技术研究35CrMo钢在不同pH的H2S溶液中的腐蚀行为,通过慢应变速率拉伸试验和U形弯试样浸泡试验研究35CrMo在不同pH和温度条件下的H2S介质中的应力腐蚀开裂行为与机理。结果表明,35CrMo钢在酸性H2S环境下SCC敏感性较高,随着介质的pH降低,35CrMo钢的应力腐蚀敏感性增加,腐蚀速率加快。pH降低能够较大地促进35CrMo钢阴极过程的进行,导致腐蚀速率和充氢电流密度均相应增大,从而导致局部阳极溶解作用和氢脆作用增大。在温度为15~90℃,35CrMo钢应力腐蚀敏感性不同,35℃和90℃条件下的应力腐蚀敏感性大。在酸性H2S环境下35CrMo钢的应力腐蚀机制是以氢脆为主,阳极溶解为辅的协同机制。     

残余拉应力对304不锈钢电化学腐蚀行为的影响

将304不锈钢制成U型弯曲试样并卸载,对卸载后拉伸面的残余应力进行了测试,研究了不同曲率半径(即不同残余拉应力)弯曲试样拉伸面在稀硫酸溶液中的电化学腐蚀行为。结果表明:卸载后U型弯曲试样拉伸面的残余应力为拉应力,残余应力值随曲率半径的减小而增大;随着残余拉应力的增大,试样的致钝电流密度逐渐增大,维钝电流密度也随之增大,钝化膜的修复能力减弱,抗孔蚀能力变差;残余拉应力越大,位错密度越高,腐蚀电流也越大。     

G105钻杆在不同氢离子浓度溶液中的腐蚀行为

通过慢应变速率拉伸试验(SSRT)与电化学试验,研究了G105钻杆在不同氢离子浓度HAc/NaAc缓冲溶液中的腐蚀行为,研究了SSRT试样的断口形貌及应力腐蚀机理。结果表明:随着氢离子浓度增大(即随着pH减小),G105钻杆的应力腐蚀敏感性和自腐蚀电流密度逐渐增大;断口形貌均呈脆性断裂,主裂纹有明显的分支裂纹;应力腐蚀机理为阳极溶解型,酸性溶液中的部分氢原子进入裂纹,加速了应力腐蚀开裂的进程。     

304不锈钢在连多硫酸中的应力腐蚀研究

采用慢应变速率拉伸试验(SSRT)、扫描电镜断口分析以及金相显微组织分析等方法对304不锈钢连多硫酸应力腐蚀开裂(PSCC)行为进行了研究。研究结果表明,固溶态和敏化态304不锈钢都具有PSCC敏感性,并且随着连多硫酸浓度的增加,PSCC敏感性也随之增大;304不锈钢在连多硫酸中的应力腐蚀开裂属于沿晶开裂机制;敏化处理及Cl-的加入均会提高304不锈钢PSCC敏感性。     

喷丸处理对AISI304钢焊缝在NaCl水溶液中应力腐蚀行为的影响

对AISI304不锈钢氩弧焊缝表面进行了喷丸处理,通过光学显微镜和扫描电镜对材料表面及断口的微观组织进行了观察,用X射线应力衍射仪测试了喷丸处理前后试样的残余应力,并进行了在NaCl水溶液中的应力腐蚀试验。结果表明:喷丸处理前,AISI304不锈钢焊缝在NaCl溶液中具有明显的应力腐蚀开裂敏感性,应力腐蚀裂纹断口表现为脆性断裂,属于穿晶型裂纹;喷丸处理后表面获得了组织细化的硬化层,残余压应力有极大提高,有效地降低了不锈钢焊缝的应力腐蚀开裂倾向。     

304奥氏体不锈钢在H_2S+Cl~-+CO_2+H_2O环境下的慢应变速率拉伸腐蚀试验研究

通过慢应变速率拉伸腐蚀试验(SSRT),研究了304奥氏体不锈钢在H_2S+Cl-+CO_2+H2O复杂介质环境下的应力腐蚀敏感性,借助扫描电镜(SEM)、能谱分析仪(EDS)分析了断口形貌和腐蚀产物性质。在环境因素中主要考虑了H_2S浓度、Cl-浓度、CO_2浓度这三种介质参数单独或交互作用对材料应力腐蚀敏感性的影响。通过对试验数据进行逐步回归分析,建立了应力腐蚀敏感性指数随介质参数变化的数学模型,同时分析了各介质参数对304奥氏体不锈钢应力腐蚀影响的显著性。     

400℃时效对304不锈钢晶间敏化行为的影响

采用双环电化学动电位再活化法（ EPR）对400℃时效处理后的304不锈钢试样进行晶间腐蚀试验,并采用金相法观察试验后试样贫铬区的形态特征。研究结果表明,固溶态304不锈钢在400℃时效10 h条件下,敏化度未见增大,晶间腐蚀敏感性并未加大;650℃敏化后304不锈钢在400℃时效10 h条件下,随着时效时间的延长,敏化度则显著增大,晶间腐蚀敏感性也随之加大。敏化态304不锈钢即使在低温条件下,其晶间腐蚀敏感性也会随着时效时间的延长而逐步增大,因此,304不锈钢的固溶处理是十分重要的,对于未经固溶处理的304不锈钢需要严格控制热加工工艺参数,杜绝敏化度的进一步增大,以避免腐蚀事故的发生。     

阳极溶解型应力腐蚀损伤中的能量问题研究

材料的损伤作为一种不可逆的热力学过程,它的发展和演化都伴随着能量的耗散.文中在热力学基础上,应用损伤力学对应力腐蚀损伤过程中的能量问题进行探索性研究.阳极溶解型应力腐蚀中的电化学过程本身是一个材料损伤的过程,从能量学角度可看作是体系能量发展变化过程中的耗散因素.通过在纯机械损伤热力学过程中加入电化学过程,建立应力腐蚀损伤导致能量耗散的动态平衡关系,提出应力腐蚀损伤耗散势的概念,给出应力腐蚀中所涉及的耗散强度量及其广延量的关系表达,依此建立起在损伤力学理论框架基础上的应力腐蚀定量分析研究.     

SO_2质量分数对污染海洋大气环境中高强钢E690腐蚀行为的影响

采用干湿交替腐蚀试验方法,结合电化学测试、锈层截面和腐蚀产物X射线衍射(X-ray diffraction,XRD)分析,研究SO_2质量分数对E690钢在模拟污染海洋大气环境中腐蚀行为的影响。结果表明,海洋大气环境中的SO_2改变了E690钢海洋大气腐蚀的电化学机制,使得极化曲线的阳极分支由弱钝化特征转变为活性溶解特征,阴极分支由氧扩散过程控制转变为氧扩散和析氢反应共同控制,因而大大促进了阳极和阴极的电化学反应过程。同时,SO_2又显著促进α-Fe OOH的生成和Ni、Cr合金元素在内锈层中的富集,大大促进锈层的致密化,使均匀腐蚀速率逐渐减低,并促进锈层底部点蚀坑的生长。随着模拟溶液中Na HSO_3浓度的增加,E690钢在60 d内的平均腐蚀速率逐渐增加,当Na HSO_3浓度达到0.03 mol/L时,又出现一定程度的降低;同时,锈层底部的点蚀坑随Na HSO_3浓度的增加显著长大。     

Discussion of ultrashort voltage pulses electrochemical micromachining: a review

One of the most effective way of electrochemical machining (ECM) accuracy increase is to carry out process with application of voltage pulses. In one of the variants of ECM, ultra short (nono- or picosecond range) voltage pulses are applied. It gives possibility to achieve high localization of electrochemical dissolution process and allows to machine microparts with accuracy less than 0.01 mm. However, because of the process principles, this variant of ECM has number of limitations which stop its wider application in micromanufacturing industry. Based on the literature review, the physical principles of ultrashort voltage pulses electrochemical machining were presented and anodic dissolution localization issues were discussed. Also, differences between other electrochemical machining variants were underlined. It gave possibility to identify limitations and future perspectives of industrial applications.     

Chemical aspects of wear of alumina ceramics

In our investigation, the effects of the tribochemically-induced dissolution of alumina ceramics and modulation of near-surface forces (surface charge) within the tribocontact were studied. The wear and friction behaviors of alumina were investigated using a reciprocating sliding test in different chemical environments. The samples for the tests were hemispherical pins and plates of polished alumina, both prepared by a near-net-shaping method.

The sliding tests were conducted in water-based liquids with different pH values or with the addition of a polyelectrolyte to control the surface charge at solid surfaces. The coefficient of friction was continuously recorded during the tests and the wear-loss was subsequently determined for all samples. The results show a significant effect of the chemical agents on the coefficient of friction as well as on the material-removal rate in different aqueous media. The results are discussed in terms of the chemical and electrochemical properties of the materials in the tribocontact.     

Electrochemical micromachining with wet stamping: Instrument design and experimental investigation

This paper presents a novel micromachining approach named electrochemical wet stamping (E-WETS) for the fabrication of microstructures on metals and semiconductors. The E-WETS allows the direct imprinting of microstructures on an agarose stamp into workpiece through a selective anodic dissolution process. According to the characteristics of the E-WETS process, an optimized instrument which consists of a positioning stage and a force sensing module is developed. An orientation head is designed for the precise stamp-workpiece parallelism alignment, which ensures the uniform micropatterns on the workpiece. The technique of short voltage pulse is applied to the E-WETS to improve the surface roughness and precision of the fabricated microstructures. Experiments are conducted to investigate the influences of pulse duration on the machining performances. Then, micromachining experiments on aluminum and nickel are carried out under the optimum conditions. The experiment results indicate that the E-WETS is an effective method and the developed instrument can well meet the requirements of the E-WETS process.     

Selective and localized embrittlement of metal by cathodic hydrogenation utilizing electrochemical jet

Electrochemical jet processing (EJP) is an easy-to-implement technology for creating complex microstructures based on anodic dissolution without requiring specially designed cathodes. In this study, a new electrolyte-jet-based surface modification method based on the principle of cathodic hydrogenation, namely, electrochemical jet hydrogenation (EJH), was proposed for the first time to selectively modify the material in aspects of its brittleness. In this method, a workpiece is innovatively set as the cathode, and hydrogen evolution occurs locally on the cathode surface within the jet impinging area, leading to a localized H-treatment of the cathode material. The hydrogen-material interaction can alter the surface material property and result in localized surface modification, for example, material ductile-brittle transition by hydrogen embrittlement (HE). In this research, the proposed method was validated on niobium metal. According to the results, evident localized embrittlement was achieved, and the degree of embrittlement was precisely controlled by adjusting the electrochemical parameters mainly including current density and processing time. As a selective surface modification method, EJH can be applied as an assistive technology in hybrid machining of difficult-to-machine superalloys where localized surface modification of ductile-brittle transition is expected.     

混气电解加工探讨

电解加工是利用金属在电解液中发生阳极溶解反应而去除工件上多余的材料、将零件加工成形的一种方法。电解加工的加工精度不仅与加工间隙有关,还与机床、工艺装备、工具阴极、工件、工艺参数等诸多因素有关,通常采用混气电解加工、脉冲电解加工、小间隙电解加工和改进电解液等措施提高加工精度。其中混气电解加工是将具有一定压力的气体与电解液按一定比例混合在一起,然后将这种混合物加入到工件的加工间隙中去进行电解加工的一种方法。混气电解加工可以缩小加工间隙,提高电解加工的加工精度和复制精度,但混气电解加工的微观不平度和不直度还不理想。从气液混合比、混气电解加工的特性以及混气电解加工的工艺三个方面对混气电解加工的原理进行一定的探讨,希望摸索一种提高电解加工精度的方法。     

Investigation of short pulse electrochemical machining for groove process on Ni-Ti shape memory alloy

Ni-Ti, a shape memory alloy (SMA), can recover from deformation to its initial shape when heated. With using this effect, Ni-Ti SMA is applied for several industries such as a medical industry, an aerospace, electrical application on a part of micro structure. The Ni-Ti alloy used for SMA is composed of approximately 56% nickel and 44% titanium. With this composition, Ni-Ti alloy cannot be machined efficiently using traditional machining tools and methods such as the lathe, milling, and drilling because it shares the poor heat dispersion characteristics of titanium. Thus, Ti-Ni SMA should be machined using non-traditional machining methods. Electrochemical micro machining (EMM) is one form of non-traditional machining that can be applied to Ni-Ti SMA. As an anodic dissolution process, EMM allows the machining of complex shapes in Ti-Ni SMA without the generation of heat and without causing tool wear during the machining process. In this study, through the experiment that making the micro-groove, the characteristic of short pulse electrochemical machining (SPECM) process is accomplished to Ni-Ti SMA. And an evaluation of various machining factors for Ni-Ti SMA is also performed, through the substitution of different types of power source and machining time, and through simulation of the material removal rate (MRR). The experimental and simulation results are analyzed and compared.     

Effects of Electrochemistry on Surface Roughness during Chemical-Mechanical Polishing of Copper

In this research, we investigated the electrochemical behavior of copper (Cu) surfaces during chemical-mechanical polishing (CMP) with alumina containing slurries. The variation of pH and the percent of oxidizer were tested against impressed anodic and cathodic potentials. The polarization curves as well as potential and current values were measured in order to investigate the effects of electrochemical interactions during polishing. The polishing performance was evaluated through friction, wear, and surface quality. Surface characterization was conducted using an atomic force microscope. The areas scanned contained surfaces having different post-CMP surface chemistry. In such, the electrochemical, chemical, and mechanical action could be revealed and compared in situ and simultaneously. Research results showed that in acidic environment, the low pH dominated the surface roughness over oxidizer and anodic current. At high pH, however, oxidizer and anodic current played important roles. As a result, an optimized polishing condition was proposed.     

Simulation-based fabrication of micro-helical grooves in a hydrodynamic thrust bearing by using ECMM

In hydrodynamic thrust bearing, common micro-grooves with helical or herringbone forms are generally to ensure the bearing load capacity and reduce leakage of lubricant, consistent with the design or size requirements of grooves. In this investigation, the electrical field distribution and anodic dissolution of helical grooves in electrochemical micro-machining process can be predicted by using COMSOL Multiphysics^TM software. The processing equivalent is based on the chemical composition of the workpiece. The micro-helical grooves are hollowed out of hydrodynamic thrust bearing using a DC and pulse power supply, and experiment results are compared with simulation results. The experimental results demonstrate that the fine surface of helical grooves can be obtained with a depth of 4.9 μm in machining time of 3 s by using a pulse power supply of 5 kHz. To eliminate the effect of such factors as flush flow, temperature difference between workpiece and tool, and formation of hydrogen bubble barriers, the k values of these factors are considered for amendment to get more accurate simulation results.