Fe-Mn基合金电化学“内源”表面改性的研究

【作者】 刘明；

【导师】 朱雪梅； 张彦生；

【作者基本信息】 大连铁道学院 ， 环境工程， 2003， 硕士

【摘要】 本项研究的宗旨在于运用电化学方法探索一种简单的合金表面改性新途径，它将不同于现有的绝大多数表面改性工艺，不需要从外部输送某些元素或化合物至被改性合金表层。基于此科学思路，采用综合电化学技术与Auger电子能谱、X射线光电子谱仪（AES／XPS）分析，研究阳极钝化时效、临界过钝化区钝化与交流电压（A．V）载波钝化分别对Al、Cr与Si合金化的Fe-Mn-C合金在50％HNO₃水溶液或1 mol l^-1 Na₂SO₄水溶液中形成的钝化膜的组成稳定性与腐蚀抗力影响的初步规律。主要研究工作分为下述四个方面。（1）阳极钝化时效：在阳极钝化中区，随时效时间延长或钝化电位升高，合金钝化膜的稳定性、组成改善与腐蚀抗力均明显增加。以Fe-24Mn-4Al-5Cr合金为例，其在50％HNO₃溶液中阳极时效时间由15min增至5h时，所形成的钝化膜于阳极开路状态在1 mol l^-1 Na₂SO₄+0.5 mol l^-1 H₂SO₄溶液中的电位衰减时间由约300s增加至约12500s。由阳极极化曲线表征的Fe-24Mn-4Al-5Cr合金抗电化学腐蚀性能优于1Cr13不锈钢。在1 mol l^-1Na₂SO₄溶液中阳极时效表面改性的效果劣于在强氧化性50％HNO₃溶液中时效者。阳极钝化时效对钝化膜的性能与组成的影响主要取决于时效时间，阳极电位与电解液的氧化性等因素。一般在阳极钝化区内，时效时间愈长，电位愈高，电解质液氧化性愈强，则钝化膜改性的效果愈佳。（2）临界过钝化区钝化：优选出在1 mol l^-1 Na₂SO₄溶液中临界过钝化区钝化处理的参数为钝化电位1100 mV，钝化时间30 min。Fe-24Mn-4Al-5Cr合金按优化参数在1 mol l^-1 Na₂SO₄溶液中过钝化区钝化后再于阳极开路状态在1 mol l^-1 Na₂SO₄+0.5 mol l^-1 H₂SO₄溶液中其钝化膜的电位衰减时间（T_d）大约为5400s。（3）A．V．载波钝化：在1 mol l^-1 Na₂SO₄溶液中，优选的A．V．载波钝化参数为交流方波周期300 ms，波幅380 mV，载波钝化时间10 min，方波叠加于阳极钝化区中点电位620 mV上。Fe-24Mn-4Al-5Cr合金按上述条件经载波钝化后在1 mol l^-1 Na₂SO₄+0.5 mol l^-1 H₂SO₄溶液中的电位衰减时间（T_d）约为4000s，较阳极钝化区中点620 mV钝化5 h的T_d延长约1200s。（4）不同钝化方法所得钝化膜的深度剖面AES／XPS分析结果说明，阳极钝化时效、临界过钝化区钝化大连铁道学院工学硕士学位论文与AC载波钝化均能增强钝化膜中Al与Cr的富集及Fe与Mn的贫乏。腐蚀抗力的增高归因于A1203与Cr203富集和Fe与Mn氧化物的贫乏，同时使有效的氧化物阻挡层增厚。在经临界过钝化电位改性后形成于re一24Mn一4AI一ser合金上的钝化膜中，其Cr3气ox与Mn3气Ox价态的结合能相对较高。文末，对上述三种钝化改性方法的电化学过程与钝化层的形成机理作了初步的简要讨论。更多还原

【Abstract】 The aim of the present investigation is to explore a simple surface modified process by using electrochemical methods, which are not required to transport certain elements or compounds to surface of alloys. In terms of this idea, the effects of anodic passivation aging, critical transpassivation and alternating voltage (A. C.) modulated passivation on the stability, constitution and corrosion resistance of passive film formed on Fe-Mn base alloying with Al, Cr and Si in 50% HNO3 solution or 1mol l-1 Na2SO4 solution were studied by way of combined electrochemical examination and Auger electron spectroscopic (AES)/X-ray photoelectron spectroscopic (XPS) analysis. (1) Anodic passivation aging: With increasing the aging time or the passivating potential in anodic passive region, the stability, improvement of constitute and corrosion resistance of passive film obviously increased. For an example of Fe-24Mn-4Al-5Cr alloy, with increasing anodic passivation time in 50% HNO3 solution from 15 min to 5 h, the activation time(Ta) of passive film in 1 mol l-1 Na2SO4+0.5 mol l-1 H2SO4 solution extended from about 300 s to above 12500 s, and the corrosion resistance of Fe-24Mn-4Al-5Cr alloy characterized by polarization curve in 1 mol l-1 Na2SO4 solution is superior to that of Fe-13Cr-0.1C SS. The modified efficiency of passive film for anodic aging in 1 mol l-1 Na2SO4 solution is inferior to that in strong oxidizing 50% HNO3 solution. The effect of anodic aging on the property and constitute of passive film mainly depend on the aging time, anodic potential and oxidizing of electrolyte. The higher the anodic potential, the longer the aging time and the stronger the oxidizing of electrolyte, the better the property and constitute of passive film aged. (2) Passivating at critical transpassivation potential: The passivating of Fe-24Mn-4Al-5Cr alloy in 1 mol l-1 Na2SO4 solution was performed under the optimal parameters of critical potential 1100 mV and passivation time 30 min. The potential decline time for passive film in 1 mol l-1 Na2SO4+0.5 mol l-1 H2SO4 solution is about 5400 s. (3) Alternatingvoltage(A.C.) modulated passivation: The effect of AC- modulation passivation on the corrosion resistance of Fe-24Mn-4Al-5Cr alloy in 1 mol l-1 Na2SO4 solution was studied by AC square wave of optimal parameters with duration of 300 ms and magnitude of 380 mv and the modulated passivation time of 10 min. The AC square wave superimposed onto the DC potential of 620 mv in the medium of anodic passivation region. The results indicate that AV modulation increases the potential decline (Td) of passive film in 1 mol l-1 Na2SO4+0.5 mol l-1 H2SO4 solution from about 2800 s(anodic aging at 620 mv for 5h) to about 4000 s. The results of depth profiles of passive film using AES/XPS analysis show that the anodic passivation aging, critical transpassivation treatment and AC-modulated passivation enhance the enrichment of Al and Cr, and the depletion of Fe and Mn in passive film. The increase of corrosion resistance is attributed to Al2O3 and Cr2O3 enrichment and depleting of Fe and Mn depletion in the passive film and thickening the effective barrier layer of oxides. In passive film of Fe-24Mn-4Al-5Cr alloy modified by transpassivation, the valence state of Cr3+-oxand Mn3+-ox present relatively higher binding energy. Finally, the electrochemistry and the formation of passive film of the three passivating modification has been discussed in brief.更多还原