开尔文探针技术检测不同表面粗糙度不锈钢早期点蚀敏感性

采用开尔文探针技术测量不同表面粗糙度不锈钢表面的功函数,得到功函数对应的粗糙度关系。其中表面粗糙度为0.25μm的不锈钢试样的功函数最低,为(-450±15)eV,随着表面粗糙度减小到0.10μm,功函数则升高到(-200±5)eV。并采用三维视频显微镜技术对不锈钢早期点蚀坑进行分析,从而了解不锈钢表面状态对点蚀敏感性的影响。结果表明,表面粗糙度高的不锈钢表面功函数波动很大,点蚀敏感区易发生点蚀,与三维视频显微镜监测结果一致。     

利用SECM技术研究304不锈钢的点蚀行为

采用扫描电化学显微镜(SECM)技术,结合电导率和循环伏安测试,研究了304不锈钢在NaCl溶液中的点蚀行为。结果表明,点蚀早期阶段,在不锈钢表面首先产生不稳定的电活性点;点蚀形成的过程中,这些电活性点或消失或成为稳定点蚀坑,并同时出现新的电活性点。电活性点的产生与消失及点蚀的形成是同时发生的。NaCl溶液的电导率与其所含Fe2+浓度有关,Fe2+浓度越高,超微电极探针检测到的稳态电流越大。     

重力对304不锈钢点蚀行为的影响

采用恒电位极化法、电化学阻抗谱和三维视频显微镜研究了304不锈钢在3.5％ NaCl溶液中水平放置和垂直放置时的点蚀行为.结果表明,试样垂直放置比水平放置更易达到稳定点腐蚀,由于重力作用使垂直放置的蚀孔内腐蚀产物更易扩散到孔外,加速点蚀的诱发和亚稳态点蚀向稳态点蚀的转变.阻抗谱等效电路中元件参数的分析结果表明,垂直放置的试样表面局部腐蚀比水平放置的更严重.     

表面粗糙度对304不锈钢早期点蚀行为影响的电化学方法

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4种不同表面粗糙度304不锈钢电极在质量分数为3％的NaCl溶液中的早期腐蚀行为.随着不锈钢电极表面粗糙度的下降,304不锈钢自腐蚀电位与点蚀电位均有所上升;电荷转移电阻噪声电阻明显升高,而电位标准偏差与电流标准偏差则有所降低;粗糙度0.25μm的电极在阻抗谱低频区出...     

南海大气环境下304不锈钢的点蚀特性研究

目的 研究南海大气环境中服役的304不锈钢的点蚀原因与机理。方法 以不同暴露周期的304不锈钢试样为研究对象,采用动电位极化、电化学交流阻抗谱、扫描电镜和Kelvin 探针技术对其进行分析研究。结果 随着暴露时间的延长,304不锈钢表面的点蚀坑数量和深度均逐渐增加,其极化曲线中,钝化区间缩短,点蚀电位负移,阳极极化曲线斜率明显减小,并出现反复再钝化现象,钝化曲线逐渐消失,同时阻抗测试中的膜层电阻越来越小。SEM分析表明,304不锈钢暴露初期出现不连续的点蚀,点蚀坑向纵深发展,暴露后期出现点蚀群,局部有多个点蚀坑连成一片形成溃疡状的腐蚀表面,同时随暴露时间的延长,扫描试样微区的Kelvin表面电位不均匀性逐渐增强。结论 304不锈钢试样的耐蚀能力随暴露时间的增加而不断下降,点蚀现象不断增加。暴露初期,点蚀坑主要向纵深发展;暴露后期,点蚀坑的宽度达到一定程度后,本体溶液向坑内迁移,稀释了坑内溶液的酸度,点蚀坑向纵深和横向同时发展。     

NiCrWFeSiBCCo合金涂层的组织与耐空蚀性

采用超音速火焰喷涂技术,在1Cr18Ni9Ti不锈钢基体表面制备NiCrWFeSiBCCo合金涂层. 采用金相显微镜(OM)、超景深体视显微镜(SM)、扫描电镜(SEM)观察涂层的显微组织和空蚀前后表面的微观形貌;采用表面粗糙度测试仪和显微硬度测试仪对涂层表面粗糙度和显微硬度进行表征;采用X-Ray衍射仪(XRD)分析涂层的相组成;采用磁致伸缩空蚀试验仪测定涂层的空蚀性能,并与1Cr18Ni9Ti不锈钢的空蚀性能进行比较. 结果表明,采用超音速火焰喷涂(HVOF)制备的NiCrWFeSiBCCo涂层组织均匀,结构致密(平均孔隙率为0.63%),硬度为1 004 HV,NiCrWFeSiBCCo涂层的抗空蚀性能明显优于1Cr18Ni9Ti不锈钢.     

阴极面积对3.5%NaCl溶液中304不锈钢稳态点蚀生长速率的影响

采用浸泡实验、动电位极化、电化学阻抗谱和三维视频显微技术研究了阴极面积对3.5%(质量分数)NaCl溶液中304不锈钢稳态点蚀生长速率的影响,模拟了稳态点蚀的生长方式。结果表明,当NaCl溶液中的外加阴极存在时,由于外加阴极的耗氧反应,阳极电位升高,导致金属溶解速率加快。在阴阳极面积比小于64时,阳极溶解速率随着外加阴极面积的增加而增加;在阴阳极面积比达到并超过64时,阳极腐蚀速率增量趋于平缓,约为无外加阴极时的2.2倍。外加阴极存在时,FeCl3溶液中的析氢反应速率也得到提升。当304不锈钢在3.5%NaCl溶液中自然产生点蚀时,蚀孔外阴极可提高蚀孔底部金属的溶解速率。     

304不锈钢在3.5%NaCl溶液中的点蚀动力学及机理

利用激光电子散斑干涉(ESPI)、电化学噪声(EN)及三维视频显微技术研究304不锈钢在3,5%NaCl溶液中点蚀早期单个蚀孔的发展动力学及其机理.结果表明在0.05 V恒电位极化下,点蚀过程可分为4个阶段:首先,电流噪声在740 s时发生剧烈波动,钝化膜开始破裂,点蚀孕育期为740s;其次,ESPI图像在750 s时产生可见光斑,稳态蚀孔萌生期为10 s;再次,750—780 s时,蚀孔的发展速率不断增加,表明点蚀处于活性溶解期:最后,蚀孔生长速率迅速下降,发生钝化,而在793 s后,由于出现次生蚀孔,生长速率再次上升.使用三维视频显微镜观察蚀孔形貌并测量蚀坑体积的变化,印证了由腐蚀产物浓度分析法得到的单个蚀孔的生长速率,并在蚀坑底部观察到了次生蚀孔.     

温度对304不锈钢亚稳蚀孔萌生和稳态蚀孔几何特征的影响

采用恒电位极化、动电位极化、EIS和三维视频显微技术研究温度对304不锈钢在3.5%(质量分数)NaCl水溶液中点蚀行为和腐蚀形貌的影响。结果表明:随着温度由20℃升高至40℃,亚稳蚀孔萌生期变短,单位时间形核数目增多,平均峰值电流和平均峰值宽度增大,亚稳蚀孔数目增加导致稳态蚀孔出现几率增加。经0.15 V(vs SCE)恒电位极化后,单个蚀孔的点蚀电流、蚀孔体积、蚀孔口径和孔深的增长速率均随温度的升高而增加;同一温度下蚀孔口径和孔深的增长速率随时间的延长略微减缓。蚀孔表面具有不完整的花边盖,盖板完整程度随温度升高而降低。     

304不锈钢TIG熔覆钴合金涂层的耐空蚀性能

采用TIG（钨极惰性气体保护焊）熔覆方法,在304不锈钢表面制成了钴合金涂层,以目前水轮机过流部件常用材料304不锈钢作为对比材料,对涂层和304不锈钢基体进行了空蚀试验.通过光学显微镜（OM）、X射线衍射仪（XRD）、扫描电镜（SEM）及显微硬度测量等手段研究了涂层的组织形态和耐空蚀性能并分析了原因.结果表明,显微硬...     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。