摘要
目的研究40CrNiMo钢在模拟海洋环境中的锈层及电化学性能初期演化规律。方法采用中性盐雾试验模拟海洋大气环境,通过光学显微镜、EDS、XRD等手段表征40CrNiMo钢内、外锈层微观结构及成分的变化。通过动电位极化、交流阻抗谱及微区电化学技术研究电化学性能的演化规律。结果40CrNiMo钢在盐雾环境中由点蚀逐渐发展为均匀腐蚀,最大腐蚀坑深度的演化规律为d=87.787t^(0.325),腐蚀动力学规律为ΔW=6.091t^(0.738)。盐雾4 d后锈层出现分层,7 d后内锈层显著增厚。黄色疏松外锈层主要成分为γ-FeOOH;黑色致密内锈层主要成分为α-FeOOH和Fe_(3)O_(4),并且在与基体接触界面出现Cr元素富集。极化曲线与EIS测量结果具有较好的相关性,表明40CrNiMo钢的腐蚀速率先增大后减小再增大;而SKP测量结果显示,盐雾环境中试样表面迅速形成阴、阳极区,盐雾7 d后试样表面Volta电位由225 mV持续增大至884 mV,盐雾11 d后降低至609 mV。结论盐雾1 d后锈层疏松多孔,为反应的发生提供了湿润的环境,加快腐蚀速率。锈层随盐雾时间的延长逐渐增厚致密,氧还原反应被抑制,对基体的保护作用愈发凸显;盐雾7 d后,锈层中γ-FeOOH还原反应的活性逐渐增强,阴极同时发生氧还原与腐蚀产物还原2个平行的阴极反应,反应速率增快后趋于稳定。
In order to study the initial evolution of rust layer and electrochemical properties of 40CrNiMo steel in simulated marine environment,in this paper,the neutral salt spray test method was used to simulate the marine atmospheric environment.The changes of microstructure and composition of inner and outer rust layer of 40CrNiMo steel were characterized by Optical Microscope(OM)and XRD,the redistribution process of Cr element in rust layer was studied by EDS line scanning,the evolution of electrochemical properties were studied by potentiodynamic polarization and EIS,the Volta potential and its distribution on the sample surface were studied by scanning Kelvin probe(SKP).The initial corrosion behavior(0-11 d)of 40CrNiMo steel in neutral salt spray environment with NaCl content of 5%gradually developed from pitting corrosion to uniform corrosion,the evolution law of the maximum corrosion pit depth is d=87.787t^(0.325),the corrosion kinetic characteristics accord with the law of power function,the fitting result isΔW=6.091t^(0.738),which show that the rust layer have a certain protective effect on the metal matrix.The rust layer was obviously stratified after 4 days of salt spray,and the inner rust layer was significantly thickened after 7 days.XRD results show that the yellow loose outer rust layer is mainly composed ofγ-FeOOH;the black dense inner rust layer is mainly composed ofα-FeOOH and Fe_(3)O_(4),and the EDS line scanning test results show that Cr element enrichment occurs at the interface with the matrix.The polarization curves show that the corrosion process was controlled by cathodic reaction,and the corrosion current density first increase,then decrease and finally increase.The EIS measurement results show that the charge transfer resistance first decrease,then increase and finally decrease.The polarization curves have a good correlation with the EIS measurement results,which show that the corrosion rate of 40CrNiMo steel first increase,then decrease and finally increase in the neutral salt spray environment.The SKP measurement results show that the cathode and anode regions were rapidly formed on the sample surface in salt spray environment,the Volta potential range on the surface of the non corroded sample was 225 mV,which increase to 884 mV after 7 days of salt spray and decrease to 609 mV after 11 days of salt spray.Therefore,it is concluded that after 1 day of salt spray,the rust layer of 40CrNiMo steel was loose and porous,which provide a humid environment for the reaction and speeds up the corrosion rate.With the increase of salt spray time,the rust layer gradually thickened and densified,meanwhile Cr element were enriched in inner rust layer,which lead to the inhibition of oxygen reduction reaction and the protective effect on the matrix became more and more prominent;after 7 days of salt spray,the activity ofγ-FeOOH reduction reaction in the rust layer gradually increased,and two parallel cathodic reactions of oxygen reduction and corrosion product reduction occurred at the same time.the reaction rate tended to be stable after increasing.
作者
吴省均
陈跃良
卞贵学
张勇
王安东
黄海亮
魏梓林
WU Xing-jun;CHEN Yue-liang;BIAN Gui-xue;ZHANG Yong;WANG An-dong;HUANG Hai-liang;WEI Zi-lin(Naval Aviation University Qingdao Campus,Shandong Qingdao 266041,China)
出处
《表面技术》
EI
CAS
CSCD
北大核心
2022年第5期234-244,共11页
Surface Technology
基金
山东省高等学校“青创科技计划”(2020KJA014)。
关键词
40CRNIMO钢
盐雾试验
锈层
电化学性能
微区电化学
40CrNiMo steel
salt spray test
rust layer
electrochemical properties
micro area electrochemistry
