纳米化对304不锈钢电化学腐蚀行为影响的研究

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	纳米化对304不锈钢电化学腐蚀行为影响的研究
	潘晨
学位类型	博士
导师	王福会
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	腐蚀科学与防护
关键词	纳米化钝化膜生长机制点蚀原子力显微镜 Nanocrystallization Growth Mechanism Of Passive Film Pittiong Corrosion Afm
摘要	"与同成分的传统粗晶合金相比，采用磁控溅射技术制备的溅射纳米晶薄膜具有更优异的耐腐蚀能力。前期大量研究结果表明纳米化会显著影响材料表面形成钝化膜的各项性能，但关于纳米化如何影响决定钝化膜性能的钝化膜生长机制以及溅射纳米晶薄膜材料的点蚀行为目前尚不明确，有待进一步详细研究；另外，虽然前期研究采用宏观测试的方法发现了材料的整体腐蚀规律，但具体、深入的原位微观机制尚不清楚。因此，本论文针对普通商用304不锈钢及其溅射纳米晶薄膜在含氯离子的常温水溶液中的电化学腐蚀行为(包括钝化行为和点蚀行为)开展系统研究。采用传统电化学测试手段与原子力显微镜原位观测相结合的方法，从钝化膜生长机制和钝化膜性能两方面阐述其钝化行为，从亚稳态点蚀和稳态点蚀两方面分析其点蚀行为，研究溅射纳米晶材料的电化学腐蚀行为，并深入探讨纳米化作用机制，为进一步改善304不锈钢的耐腐蚀能力提供必要的理论依据。实验结果表明普通304不锈钢、轧制纳米块体及溅射纳米晶薄膜在0.05M H2SO4 + 0.2M NaCl酸性溶液中钝化膜的生长机制差异较大。利用原子力显微镜原位观测与电化学测试相结合的方法对钝化膜的生长过程进行原位、连续观测发现，不同于304不锈钢的连续形核机制，同成分的两种纳米材料表面钝化膜的形核机制转变为瞬时形核，即纳米化促进钝化粒子核形成。三种材料钝化膜的生长方式相同，均为三维生长，但两种纳米材料钝化膜的生长速度更快。其中，滚压轧制法促进了钝化膜在二维尺度(x轴和y轴)上的生长。磁控溅射法则加快了钝化膜在三维尺度(x轴、y轴和z轴)的生长速度，使钝化膜由单层结构转变为多层结构。对304不锈钢及溅射纳米晶薄膜钝化膜性能进行研究发现，纳米晶薄膜钝化膜的瞬时形核机制以及钝化膜在二维尺度(x轴和y轴)上的快速生长，提高了纳米晶薄膜钝化膜的致密性。溅射纳米晶薄膜钝化膜的多层结构，导致膜层间缺陷增加、不匹配性增大，表现为钝化膜中载流子密度增加。机理分析表明，纳米晶薄膜大量晶界的存在为合金元素的快速扩散提供通道，加快了钝化膜在三维尺度(z轴)上的生长速度，增加了钝化膜中Cr/Fe氧化物的比例；另外，晶粒尺寸的减小会降低材料表面氯离子吸附量。因此，钝化膜的快速生长、膜中具有较高的Cr/Fe氧化物比例以及膜中无氯离子掺杂是溅射纳米晶薄膜耐蚀能力提高的主要原因。将随机理论与电化学噪声统计分析方法相结合，再配以原子力显微镜原位、连续观测，对普通304不锈钢及其溅射纳米晶薄膜在3.5%NaCl溶液中的点蚀行为进行详细研究，结果表明：相对于304不锈钢材料而言，纳米晶薄膜的点蚀萌生位置发生改变，粗晶材料点蚀萌生源于大尺寸MnS夹杂物的溶解；而由于晶粒尺寸减小，MnS夹杂物弥散分布致纳米晶薄膜的点蚀萌生位置转变为纳米材料表面钝化粒子团簇的边界处。由此，溅射纳米晶薄膜亚稳态点蚀事件发生更为频繁。但由于纳米晶薄膜材料促进了元素的快速扩散，使其亚稳态点蚀自修复能力更强，不容易发生向稳态点蚀的转变，因此提高了纳米材料的耐点蚀性能。利用电化学噪声结果对304不锈钢及溅射纳米晶薄膜在测试溶液中的稳态点蚀形成速度、生长速度及生长概率等进行统计分析，结果表明：与304不锈钢相比，纳米晶薄膜稳态点蚀的形成和生长过程都受到抑制。分别采用金相显微镜和原子力显微镜对两种材料点蚀坑形状进行统计分析发现，两者稳态点蚀坑的形状差异在于304不锈钢为半椭圆形，而纳米晶薄膜是浅碟形。304不锈钢与溅射纳米晶薄膜稳态点蚀坑的生长机制不同，导致两者耐点蚀能力存在较大差异，溅射纳米晶薄膜耐点蚀能力更强。"
其他摘要	"The corrosion resistance of nanocrystalline thin film prepared by magnetron sputtering technique has been improved compared to conventional coarse stainless steel with the same chemical composition. Many studies indicated that nanocrystallization could influence the corrosion performance of passive film. However, it is uncertain how nanocrystallization effects on the growth mechanism which directly determines the performance of passive film and on the pitting corrosion behavior. In addition, although the previous investigations revealed the whole corrosion regular, there was no in-situ micro-mechanism. Therefore, the electrochemical corrosion behavior including passive and pitting corrosion of 304 stainless steel and its sputtered nanocrystalline (NC) thin film has been investigated in solution containing Cl- at room temperature. In order to reveal the electrochemical corrosion behavior of NC thin film and investigate the nanocrystallization mechanism, both conventional electrochemical measurements and in-situ AFM observation were employed to study the passive behavior including the growth mechanism and performance of passive films on two materials and to analyze the pitting corrosion behavior including metastable and stable pit process. These results are helpful to the theoretical base for improving the corrosion resistance of 304ss in future. The growth mechanism of the passive films on bulk nanocrystalline (BN) 304ss and NC thin film in 0.05 M H2SO4 + 0.2M NaCl solution are different from that on 304ss. The growth process of passive films was observed by the combination of in-situ AFM and electrochemical measurements. The results indicated that the nucleation mechanism of passive films on two nanocrystalline materials changed into instantaneous mechanism which was different from the progressive mechanism of 304ss. That is to say, nanocrystallization promoted the formation of passive particles. Although growth manner of passive film on three samples is three-dimensional, the growth rate of passive film on two nanocrystalline materials is higher than that on 304ss. Deep rolling method promoted the growth rate in two-dimensional(x-direction and y-direction) of passive film. However, Magnetron sputtered methods accelerated the growth rate in three-dimensional (x-direction, y-direction and z-direction), which altered the growth structure of passive film from single layer to multi-layer. The study on the corrosion performance of passive films on 304ss and NC thin film demonstrated that the instantaneous nucleation mechanism and fast growth in two-dimensional (x-direction and y-direction) of passive films on NC thin film improved the compactness of passive films. The multi-layer nature of passive films on the NC thin film increased the quantity of defects and dislocations in the film which was expressed as the increase of carrier densities. Larger volume of grain boundaries in NC thin film promoted diffusion of elements, which accelerated the growth rate of passive film in three-dimensional (z-direction) and increased the ratios of Cr oxides to Fe oxides in the passive film. In addition, small grain size decreased the adsorption of chloride ions on the surface. The improved corrosion resistance of NC thin film was attributed to the fast growth of passive films, high ratios of Cr oxides to Fe oxides and non incorporation of chloride ions in the passive film. The pitting corrosion behavior of 304ss and NC thin film in 3.5% NaCl solution has been investigated by electrochemical noise and in-situ AFM observation, and the experimental data was analyzed based on stochastic theory. The results indicated that compared with 304ss, the pit initiation site on NC thin film has changed.The pit initiation on 304ss was attributed to the dissolution of large-size MnS inclusion. Due to decrease of grain size, the dispersion of MnS inclusion in the NC thin film caused the pit initiation site changing into at the boundaries of oxide particles. The change in the pit initiation site and the outstanding repassivation ability of NC thin film determined that metastable pit events occurred more frequently and the probability of stable pits developing from metastable pits was lower than that of 304ss, which improved the pit corrosion resistance of NC thin film. The formation rate, growth rate and growth probability of stable pits on 304ss and NC thin film in test solution have been studied according to electrochemical noise data. The results demonstrated that the formation and growth process of stable pits on NC thin film had been retarded. The morphology of stable pits on 304ss and NC thin film has been analyzed by microscope and AFM observation, respectively. The results indicated that the morphology of stable pits cavity on 304ss was different from that on NC thin film.The previous one is a semi-elliptic shape while the latter on is a shallow-disk shape. The difference between growth mechanisms of stable pits on two materials led to different corrosion resistance, thus enhancing the pit corrosion resistance of NC thin film."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64462
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	潘晨. 纳米化对304不锈钢电化学腐蚀行为影响的研究[D]. 北京. 中国科学院金属研究所,2012.