微观结构和微量元素对铝箔腐蚀结构的影响

观察了经300℃退火并分别快冷和慢冷的铝箔表面的电化学腐蚀结构.利用二次离子质谱仪检测了铝箔表面区域Fe、Si、Cu、Mg等微量元素的分布.结果显示:Mg在铝箔外表面的富集高于铝箔内部4个数量级,Fe、Si的富集程度约高2个数量级,而Cu则不足1个数量级.退火后慢速冷却会造成富集于表面的微量元素偏聚于晶界和位错周围,从而会加重腐蚀结构的不均匀性并降低铝箔的比电容.     

退火工艺对低压铝箔氧化膜和比电容的影响

纯度99.988%的铝箔在300,400和500℃分别进行0.5,1和2h真空退火,然后利用电容法,间接测出退火箔的氧化膜厚度.用扫描电子显微镜观察部分退火箔的腐蚀形貌,测出相应的比电容.结果表明,在400℃退火时,铝箔的氧化膜厚度最小,300℃居中,500℃最大.在300℃退火时,随着保温时间的延长,铝箔的氧化膜厚度减小;而在400℃和500℃退火时,氧化膜厚度增大.500℃退火的铝箔,表面微量元素的分布接近于平衡状态,分布较均匀,铝箔表面腐蚀孔坑较细小,蚀坑密度大,比电容较高.而低温退火的箔样,微量元素偏聚在铝箔表面的位错露头附近,使铝箔表面出现大量的腐蚀孔坑,降低了比电容.     

退火方式对低压电解质电容器铝箔微量元素的分布和腐蚀性能的影响

观察了经400℃真空退火保温1h后分别随炉冷却和空冷的低压铝箔表面的电化学腐蚀结构,检测相应的比电容,利用二次离子质谱仪检测了铝箔表面区域Mg、Si、Cu微量元素的分布。结果显示,在炉冷的条件下,微量元素在铝箔表面的浓度比空冷条件下的高,且分布比较均匀。在空冷条件下,微量元素更容易偏聚在表面的轧制纹、晶界等缺陷处,使箔样在轧制纹处出现不均匀腐蚀结构,不利于比电容的提高。     

酸碱预处理对高压电子铝箔腐蚀扩面的影响

目的研究高压电子铝箔在Na OH和HCl溶液中的电化学行为,分析酸、碱预处理对铝箔电化学腐蚀扩面效果的影响。方法比较铝箔在不同浓度Na OH,HCl溶液中的预处理效果。采用极化曲线获得铝箔在各预处理溶液中的电化学参数,研究其腐蚀行为。利用扫描电子显微镜观察预处理后铝箔的表面形貌,分析预处理对铝箔表面形貌的影响。观察铝箔腐蚀扩面后的蚀孔形貌及蚀孔分布,分析预处理对蚀孔的影响。结果预处理减弱了铝箔制造过程中形成的表面不均匀,提高了表面活性,使得铝箔在电化学腐蚀处理中蚀孔密度增加,分布均匀。对未预处理铝箔及经HCl和Na OH预处理的铝箔进行电化学扩面处理,发现相对于未预处理的铝箔(比电容为0.56μF/cm2),经HCl溶液预处理的铝箔比电容提高了4%~8%,Na OH溶液预处理的铝箔比电容提高更为明显,约为13%~16%。铝箔在HCl溶液中的自腐蚀电位约为-820 m V,在Na OH溶液中的自腐蚀电位约为-1720 m V,并且经计算得知,铝箔在Na OH溶液中比在HCl溶液中自腐蚀速率快。结论铝箔在Na OH溶液中腐蚀均匀,用Na OH溶液对铝箔进行预处理,可以消除铝箔轧制缺陷,提高铝箔的比电容。     

电解工艺条件对铝箔腐蚀形貌与比电容的影响

利用扫面电镜(SEM)、数字电桥研究了铝电解电容器用高压电子铝箔在硫酸+盐酸体系中进行电化学腐蚀扩面时,工艺条件对铝箔腐蚀形貌与比电容的影响规律:电解腐蚀时间对铝箔腐蚀后形貌与比电容影响较大,发孔时间延长、扩孔时间缩短,隧道孔密度增加、孔直径减小;发孔电流密度对铝箔腐蚀形貌与比电容影响较小,只要高于点蚀电流密度,小电流长时间发孔与大电流短时间发孔都可以在铝箔表面形成足够密度的蚀孔结构;电解液温度对铝箔腐蚀形貌和比电容影响较大,随着发孔液温度的提高,蚀孔密度增加、蚀孔孔径减小,隧道孔长度减小.     

晶粒及晶界特征对高锰奥氏体TWIP钢抗腐蚀能力的影响

以一种高锰奥氏体孪晶诱发塑性(TWIP)钢为实验材料,采用700~1000℃保温20 min及800℃保温10~30 min的退火工艺获得了不同晶粒尺寸分布及晶界特征分布的再结晶组织,结合EBSD技术及动电位极化曲线测试,研究了晶粒度、晶粒均匀性及晶界特征分布对该钢抗腐蚀能力的影响.结果表明,该高锰奥氏体TWIP钢的抗腐蚀能力受组织中的晶粒度及重位点阵(CSL)晶界分布比例的影响,二者的作用在再结晶的组织中因组织的均匀性不同而表现出明显差异.当再结晶过程刚刚结束,晶粒组织尚不均匀且未进入晶粒长大阶段时,平均晶粒尺寸对抗腐蚀能力的影响占主导地位.随着平均晶粒尺寸的增大,该TWIP钢的抗腐蚀能力下降.而当再结晶晶粒充分长大且晶粒尺寸分布均匀,CSL晶界所占的比例对其抗腐蚀能力的影响尤为显著.随着CSL晶界所占晶界比例的提高,该TWIP钢的抗腐蚀能力增加.     

铝箔表面化学镀锌对其在HCl-H 2 SO 4体系中电蚀性能的影响

将高压铝电解电容器用电子铝箔在含Zn2＋的5.0%NaOH溶液中实施化学镀锌处理,然后在HCl＋H2SO4电解液中进行直流电解扩面腐蚀得到腐蚀箔;采用极化曲线研究化学镀锌处理对扩面腐蚀时铝箔点蚀电流、点蚀电位的影响,利用电化学交流阻抗（EIS）研究化学镀锌处理对铝箔电解腐蚀时电化学特征的影响;使用扫描电镜（SEM）观察化学镀锌处理对腐蚀箔表面和横截面形貌的影响;测试100 V形成电压下腐蚀箔的比电容。结果表明：铝箔表面化学镀锌形成的Zn-Al微电偶有助于电蚀时降低点蚀电极反应的阻力,提高点蚀电流密度,增加铝箔表面蚀孔密度和蚀孔分布的均匀性;随着碱液中Zn2＋浓度的提高,腐蚀箔的比电容逐渐增加。     

挤压比对AZ31镁合金组织结构的影响

试验研究了挤压比对AZ31镁合金组织结构的影响.结果表明,258℃挤压变形镁合金在形变初期容易出现孪晶,再结晶晶粒一般出现在晶界和孪晶附近.挤压比小时动态再结晶晶粒平均尺寸为2 μm,动态结晶细化了晶粒.随着挤压比增大,晶粒尺寸减小,组织趋于均匀.挤压比达到16时,动态再结晶基本完成.挤压比为25时,能得到晶粒细小且均匀的组织,平均晶粒尺寸为7.3 μm.     

晶粒尺寸对超低碳IF钢耐大气腐蚀性能的影响

采用不同轧制及热处理工艺制备了化学成分相同而晶粒尺寸不同的3种超低碳IF钢试样.采用浸泡腐蚀、周浸腐蚀、原子力显微镜(AFM)及扫描电镜(SEM)微观分析、电化学阻抗测试等手段对晶粒尺寸与IF钢耐大气腐蚀性能之间的规律进行了研究.AFM及SEM微观分析结果表明,随着晶粒尺寸从15μm增加到220μm,超低碳IF钢浸泡腐蚀后晶界处的局部腐蚀更加严重,腐蚀裂纹处的深度加深,裂纹宽度变宽.超低碳IF钢晶粒尺寸从15μm增加到46μm,周浸腐蚀实验后锈层中空洞和裂纹增多,锈层电阻下降,耐候性下降;晶粒尺寸进一步增大到220μm后,锈层整体致密性得到增加,锈层电阻上升,耐候性得到增加.对晶粒尺寸影响耐大气腐蚀性能的机理进行了讨论.晶粒尺寸增大后晶界能的减少使得腐蚀表面的宏观总体缺陷数量有所减少,耐候性有所提高;但是晶粒尺寸增大后晶界处因局部腐蚀电流密度增大将会在局部造成更深的腐蚀坑槽并降低耐候性;晶粒尺寸的变化对钢铁材料耐大气腐蚀性能的影响不仅要考虑其对晶界局部腐蚀电流密度的影响,而且还必须考虑对基体整体晶界能所造成的影响.     

烧结Nd-Fe-B磁体充磁特性研究

针对稀土永磁电机装配对Nd-Fe-B不饱和充磁的技术需求,分析了磁体的取向度、微观组织结构等对磁体充磁特性的影响。提高烧结Nd-Fe-B磁体的取向度,消除大尺寸晶粒、提高富稀土晶界相分布的均匀性可以有效提高磁体不饱和充磁状态下的磁通密度。通过调整粉末粒度分布、降低晶粒尺寸、改善富稀土相分布使磁体平均晶粒尺寸由4.43μm降低到2.70μm,磁体退磁曲线的方形度由95.3%提高到96.2%,磁瓦不饱和充磁后的磁通值可以达到饱和充磁的95%以上,满足电机装配充磁要求。     

Electrochemical behavior of AISI 302 austenitic stainless steel in coal chemical high-salt wastewater

In this study, the effect of grain size and grain boundary characteristic distribution on the corrosion resistance of AISI 302 austenitic stainless steel in simulated coal chemical high-salt wastewater was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The grain size of the heat-treated sample is significantly increased and contains a greater fraction of high-angle grain boundaries (HAGBs) and twin content. As the heat treatment temperature and time increase, the passivation current density increases, which makes the passive film more susceptible to attack. The coarse-grained microstructure has exhibited worse pitting resistance due to its higher fraction of the HAGBs.     

Effect of grain size on corrosion behavior of electrodeposited bulk nanocrystalline Ni

Nanocrystalline (NC) and coarse-grained Ni with different grain sizes (from 16 nm to 2 μm) were fabricated by direct current electrodeposition. Effect of grain size on the electrochemical corrosion behavior of these Ni deposits in different corrosion media was characterized by using potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and immersion corrosion test. Results show that in the NaOH or NaCl solution, the NC Ni exhibits improved corrosion resistance with the decrease of grain size. But in H2SO4 solution, the higher grain boundary density accelerates corrosion due to no passive process and the corrosion resistance of NC Ni decreases with refining grain size. The distinct experimental results of NC Ni in corrosion behavior can be reasonably explained by the positive or negative effect of high-density grain boundaries in different corrosion media.     

Effects of cooling rate on the precipitation behavior of grain boundary carbide and corrosion resistance of 5Cr15MoV stainless steel

High-carbon and high-chromium alloy steels are prone to pitting and intergranular corrosion, which reduces corrosion resistance. The precipitation behavior of the carbides of high-carbon and high-chromium alloy steels is one of the main factors affecting pitting and intergranular corrosion of stainless steel. In this study, 5Cr15MoV stainless steel was heated to 1,200℃ and then cooled by cooling rates varying from 25 to 150°C/min. The precipitation behavior of grain boundary carbides of 5Cr15MoV steel at different cooling rates, and its effect on the corrosion resistance of materials was studied. The results show that the carbides of 5Cr15MoV steel mainly precipitate along the grain boundaries, which leads to the formation of chromium-depleted zones near the grain boundaries and reduces resistance to intergranular corrosion. It has been found that a higher cooling rate shortens the width of the Cr-depleted zone near the boundary from 0.871 to 0.569 μm, reduces the Cr-concentration gradient near the grain boundary from 36.422% to 12.667%, and suppresses the nucleus growth rate of grain boundary carbides. As the cooling rate increases, the corrosion current density decreases from 13.29 to 2.42 μA/cm². The corrosion rate is the lowest, while the cooling rate is 150°C/min. The corrosion rate decreases from 218.339 to 158.488 mm/a. The phenomenon of intergranular corrosion and pitting corrosion was found to be weakened; and thereby, it is shown that an intensive cooling rate can improve the corrosion resistance of 5Cr15MoV steel.     

Al-Zn-Mg铝合金厚板搅拌摩擦焊接头组织与分层性能

采用搅拌摩擦焊方法对14 mm厚Al-Zn-Mg铝合金进行对接焊接,研究了沿厚度方向分层切片的横向拉伸和应力腐蚀性能,揭示搅拌摩擦焊接头分层力学和腐蚀性能的不均匀性。研究结果表明,焊核区为细小的再结晶组织,焊核区从上表层到下表层晶粒尺寸逐渐减小;接头两侧的热影响区存在明显软化区;接头分层的抗拉强度波动较小,在315～330 MPa之间,断裂位置均位于前进侧的软化区;接头上、下表层在四点弯曲试验中均未发生腐蚀断裂,接头上、下表层热影响区的腐蚀敏感性最高;晶内析出相发生粗化和晶界析出相连续分布,是导致热影响区力学性能和耐蚀性能降低的根本原因。     

时效处理对CrCoMo不锈钢耐蚀性能的影响

采用循环极化和电化学阻抗谱研究了退火状态和时效状态的CrCoMo不锈钢在3．5％NaCl溶液中的腐蚀行为。结果表明,退火态CrCoMo不锈钢经时效处理后点蚀电位负移,钝化膜保护性下降,材料的耐蚀性能降低。其原因是时效处理使得第二相沿晶界析出,材料的组织均匀性变差。     

微弧氧化膜对7A52铝合金搅拌摩擦焊接头腐蚀不均匀性的影响

7A52铝合金搅拌摩擦焊接头焊核区由于发生动态再结晶，晶粒比较细小，组织呈现“洋葱环”分布，热力影响区的组织沿塑性流动方向分布，热影响区晶粒尺寸发生了明显的长大.接头组织不均匀导致不同区域的腐蚀行为不同. 结果表明，没有微弧氧化膜时，母材的致钝电流远小于焊核区及热(力)影响区，更容易钝化；当微弧氧化膜的厚度为50 μm，母材的致钝电流小于焊核区及热(力)影响区，较薄的微弧氧化膜对接头腐蚀不均匀性的改善作用不明显；当微弧氧化膜的厚度为70 μm时，接头不同区域钝化特征接近，微弧氧化膜有助于减小接头组织不均匀对接头不同区域的腐蚀不均匀的影响.     

Optimization of grain boundary character distribution for intergranular corrosion resistant 304 stainless steel by twin-induced grain boundary engineering

The effects of process parameters, pre-strain, annealing temperature, time, etc. on grain boundary character distribution (GBCD) and intergranular corrosion in thermomechanical treatment were examined during grain boundary engineering of type 304 austenitic stainless steel. Slight pre-strain annealing at a relatively low temperature resulted in excellent intergranular corrosion resistance due to optimized GBCD, i.e. the uniform distribution of a high frequency of coincidence site lattice boundaries and consequent discontinuity of random boundary network in the material. The optimum distribution can be formed by introduction of low energy segments on migrating random boundaries during twin emission and boundary–boundary reactions in the grain growth without generation of new random boundaries.     

Application of Grain Boundary Engineering to Improve Intergranular Corrosion Resistance in a Fe–Cr–Mn–Mo–N High-Nitrogen and Nickel-Free Austenitic Stainless Steel

Optimization of grain boundary engineering(GBE) process is explored in a Fe–20Cr–19Mn–2Mo–0.82N high-nitrogen and nickel-free austenitic stainless steel, and its intergranular corrosion(IGC) property after GBE treatment is experimentally evaluated. The proportion of low Σ coincidence site lattice(CSL) boundaries reaches 79.4% in the sample processed with 5% cold rolling and annealing at 1423 K for 72 h; there is an increase of 32.1% compared with the solution-treated sample. After grain boundary character distribution optimization, IGC performance is noticeably improved. Only Σ3 boundaries in the special boundaries are resistant to IGC under the experimental condition. The size of grain cluster enlarges with increasing fraction of low ΣCSL boundaries, and the amount of Σ3 boundaries interrupting the random boundary network increases during growth of the clusters, which is the essential reason for the improvement of IGC resistance.     

冷拉伸预变形及热处理对Hastelloy C-276合金晶界特征的影响

对Hastelloy C-276合金分别进行2%、6%、14%、22%、30%和54%冷拉伸预形变后经1100 ℃×15 min等温退火并水冷,采用EBSD技术分析变形量对其合金晶界特征分布和晶粒尺寸的影响。结果表明,随着变形量的增加,总的特殊晶界比例呈先下降后上升最后下降的趋势。当变形量为14%时,总的特殊晶界比例出现峰值点,达到了64.8%,同时Σ1晶界比例出现拐点,呈下降趋势,变形储存能得以释放,有利于特殊晶界的产生。此时,晶粒组织处于再结晶初始阶段。但大变形条件下的退火并不利于特殊晶界比例的提高。随着晶粒尺寸的增加,退火孪晶密度降低,选择适当的晶粒尺寸有利于晶界特征分布优化。