Insight into the corrosion evolution of Fe-based amorphous coatings under wet-dry cyclic conditions
Insight into the corrosion evolution of Fe-based amorphous coatings under wet-dry cyclic conditions
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深入了解干湿循环条件下铁基非晶涂层的腐蚀演化
DOI：
10.1016/j.electacta.2019.07.058
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发表时间：
2019
影响因子：
6.6
通讯作者：
Wang J Q
中科院分区：
文献类型：
--
作者：
Wu J;Cui J P;Zheng Q J;Zhang S D;Sun W H;Yang B J;Wang J Q
了解铁基非晶涂层在干湿循环条件下的腐蚀行为对涂层在海洋环境中的应用具有重要意义。采用电化学阻抗谱（EIS）、扫描电镜（SEM）和透射电镜（TEM）研究了涂层在干湿循环条件下的腐蚀演变过程。采用改进的传输线等效电路模型拟合EIS结果，得到准确的电荷转移电阻（Rt），并构建Rt景观图，用于涂层腐蚀的全景研究。结果表明，在干湿循环条件下，涂层的腐蚀速率呈周期性变化。在一个单一的干湿循环中，腐蚀可以分为四个阶段：由于钝化或再钝化，当涂层被润湿时，腐蚀速率的初始降低，然后由于溶液蒸发，由于集中的侵蚀性离子而缓慢增加，随后与快速的氧气传输相关的快速增加，最后随着溶液干燥而稳定。当涂层表面的溶液膜很薄时，涂层孔内外之间会形成氧浓度梯度，从而进一步促进孔内的局部腐蚀。根据Rt的景观图，涂层在最初的33个干湿循环中保持其高耐腐蚀性。但在第35次干湿循环中，其耐蚀性显著下降，并伴有局部腐蚀的发生。在65次干湿循环后，涂层由于局部腐蚀的渗透而失效。颗粒间氧化层是有缺陷的，这增强了局部腐蚀过程。
Understanding the corrosion behavior of Fe-based amorphous coatings under wet-dry cyclic conditions is of pretty importance for coating applications in marine environments. In this paper, the corrosion evolutions of the coatings under wet-dry cyclic conditions were investigated by electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Accurate charge transfer resistance (Rt) was obtained through fitting EIS results using a modified transmission line equivalent circuit model and a landscape map ofRtwas constructed for a panoramic investigation on coating corrosion. The results show that the corrosion rate of the coating changes cyclically under wet-dry cyclic conditions. Corrosion within a single wet-dry cycle can be presented as four stages: an initial decrease of corrosion rate due to passivation or repassivation when the coating is wetted, then a slow increase due to concentrated aggressive ions with solution evaporation, followed by a rapid increment associated with fast oxygen transport under ultrathin solution film and finally a stable stage as solution dries out. It is deduced that an oxygen concentration gradient can form between the inside and the outside of coating pores when the solution film over the coating is very thin, which further promotes the localized corrosion in the pores. According to the landscape map ofRt, the coating maintains its high corrosion resistance for the initial 33 wet-dry cycles. But its corrosion resistance decreases significantly in the 35th wet-dry cycle accompanied by the attack of localized corrosion. After 65 wet dry cycles, the coating fails due to the penetration of localized corrosion. The interparticle oxide layers are defective, which enhances the localized corrosion process.