【作者】 蒋继波；

【导师】 钟庆东；

【作者基本信息】 上海大学 ， 材料学， 2013， 博士

【摘要】 低碳钢作为一种重要的功能结构材料，广泛应用于化工、冶金、电子信息等领域。但其表面质软且具有较高的活性，导致低碳钢已很难满足某些特定的要求，因而迫切需要改善其表面性能，这也是目前材料科学中一个非常重要的研究方向。近年来迅速发展的表面处理技术，正日益得到广泛关注。因此，本文就低碳钢表面制备合金层及复合沉积层开展了一系列的工作，并进行了与之相关的电化学等研究，以改善和提高低碳钢表面的性能，尤其是耐腐蚀性、硬度和耐磨性。研究中，所制备的含硼层类型及相应的制备方法主要分为两类：第一类是在总结前人研究固相热扩渗方法的基础上，提出了一种基于超细粉体涂覆技术新的热扩渗方法，将负载于低碳钢表面的超细粉体，在氢气氛围中进行保温热处理，使其表面制备一层Fe-B合金层；第二类是鉴于复合沉积层具备独特的化学、物理机械性能，利用复合电沉积的方法在低碳钢表面制备了Fe-FeB、Fe-Ni/FeB及Ni-nano-B4C复合沉积层，并利用循环伏安技术（C-V）、恒电位阶跃技术（i-t）、电化学阻抗技术（EIS）分析了单一体系与复合体系的电结晶形核/长大过程。利用EIS、Tafel对制备的含硼层样品进行了耐腐蚀性能研究，同时利用电化学手段在硼酸缓冲液中，对低碳钢表面制备的含硼层表面的钝化行为进行了研究。在低碳钢表面制备的含硼层样品中，Fe-B合金层样品主要从保温温度与渗剂成分比例方面对制备的Fe-B合金层样品的表面形貌、粗糙度、耐腐蚀性能、硬度以及耐磨性等做了研究。研究结果表明，样品的腐蚀电流密度均小于基体低碳钢。保温温度对样品的腐蚀电流密度的影响趋势与对样品的腐蚀电位影响趋势一致，即随着保温温度的升高，样品的腐蚀电流密度逐渐降低。900℃时，粉体中Fe/B摩尔比为2/1时，样品腐蚀电流密度最低，此条件下制备的样品耐蚀性最好，对基体的保护能力最强，样品的微观硬度最大，耐磨性也最好。在对低碳钢表面制备Fe-FeB、Fe-Ni/FeB和Ni-nano-B4C复合沉积层的研究中，本文从复合电沉积的影响因素入手，研究了溶液中微粒的浓度、阴极电流密度、溶液pH值、施镀温度及溶液的搅拌速率对复合沉积层中粉体微粒含量的影响，并对制备的三种含硼复合沉积层相关性能进行了研究。其中Ni-nano-B4C复合沉积层样品耐蚀性能最好，Fe-Ni/FeB复合沉积层次之，而Fe-FeB复合沉积层相对较差，其耐蚀性能与基体相当。众所周知，大多数复合沉积层的一个缺点就是孔隙和内应力，适当的温度进行热处理后，将在一定程度上改善复合沉积层的孔隙和内应力缺陷。因此经热处理后，本文所制备的三种复合沉积层样品耐蚀性能有所改善。在对表面微观硬度和耐磨性的研究中发现，文中所制备的三种复合沉积层样品的硬度都明显高于基体低碳钢的表面硬度，也均表现出了较好的耐磨性。在硼酸缓冲液中，热扩渗制备的Fe-B合金层与电沉积法制备的含硼复合沉积层样品表面均拥有比基体低碳钢更好的钝化性能。低碳钢样品表面形成的钝化膜为n型半导体，Fe-B合金层样品、Fe-Ni/FeB复合沉积层样品表面形成的钝化膜也为n型半导体，膜中多数载流子密度为电子。而Ni-nano-B4C复合沉积层样品表面形成的钝化膜则表现为p型半导体的导电特征，膜内多数载流子为空穴。其制备的样品表面钝化膜中的载流子密度也都显著低于低碳钢表面形成的钝化膜中的多数载流子密度。利用经典的PDM模型计算了Fe-B合金层样品和Ni-nano-B4C复合沉积层样品表面钝化膜的点缺陷扩散系数。Fe-B合金层样品的扩散系数在10-17~10-14cm2/s的数量级，Ni-nano-B4C复合沉积层样品扩散系数在10-14cm2/s。通过对扩散系数和膜中载流子密度的定量分析后认为，Fe-B合金层样品和Ni-nano-B4C复合沉积层样品表面钝化膜的导电性都主要受膜中载流子密度的影响。更多还原

【Abstract】 Low carbon steel, as an important structural material, is widely used in many fields suchas chemical industry, metallurgy, electronic information,etc. However, due to its soft surfaceand high chemical activiey, it can not meet some specific requirements. Therefore, to improvethe surface properties of low carbon steel is an urgent and also an important research directionin material science. In recent years, the rapid development of surface treatment technology isgaining widespread attention. This paper mainly studied the alloy layer and the compositesediments on the low carbon steel surface as well as the associated electrochemical researchin order to improve the performance of low-carbon steel surface, especially the corrosionresistance, hardness and abrasion resistance.The type of coating and the preparation method are mainly divided into two categories:The first category is a new thermal diffusion method based on the ultrafine powder coatingtechnology which is proposed from the previous studies on the solid-phase thermal diffusionmethod. The ultrafine powders are loaded on the surface of the low carbon steel. Afterinsulated in hydrogen atmosphere, Fe-B alloy layer will generate on the surface of the lowcarbon steel. The second category uses composite electrodeposition method to prepare theFe-FeB, Fe-Ni/FeB and Ni-B4C composite sediment on the low-carbon steels which is basedon the unique physical and mechanical properties of composite sedimentary. The crystalnucleation/growth process in the single system and composite system were analyzed by thecyclic voltammetry (C-V), constant potential step (i-t) and electrochemical impedancespectroscopy (EIS).The corrosion resistance of the boron-containing coating was also studiedby EIS and Tafel. Meanwhile, this paper also examed the passivation behavior of low-carbonsteel surface covered with boron-containing layer.For the boron-containing layer samples, the study mainly focused on the surfacemorphology, roughness, corrosion resistance, hardness and abrasion resistance of the Fe-Balloy layer samples, which were prepared at different composition ratio and different thermalinsulation temperature. The results showed that the corrosion current density of the samplewas lower than the low carbon steel substrate. The influence trend of maintaining the temperature on the corrosion current density was the same as on the corrosion potential: thecorrosion current density of the sample decreases with the increase of the temperature ofincubation. The sample reached the minimum corrosion current density at900℃and themolar ratio of Fe/B in the powder was2/1. Under this condition, corrosion resistance wasthe best and it had the best ability to protect the matrix, the highest micro-hardness and thebest abrasive resistance.For the study of the Fe-Feb Fe-Ni/FeB and Ni-nano-B4C composite deposition layer, thispaper started from the composite electrodeposition influencing factors, including theconcentration of particles in solution, the cathode current density, pH, plating temperature andstirring rate of the solution, and further studied the related properties of three types of theboron-containing compound. Ni-nano-B4C composite sediments samples showed the bestcorrosion resistance and Fe-Ni/FeB composite sediments samples took the second place, andFe-Feb complex deposition layer samples showed relatively poor corrosion resistance whichwas similar to the matrix. One well-known drawback of most composite deposited layer is theporosity and internal stress. After heat-treatment at appropriate temperature, porosity andinternal stress of the composite deposited layer will be improved to some extent. Therefore,after heat treatment, the corrosion resistance of the three kinds of composite sedimentssamples was improved. At the meanwhile, these three kinds of composite sediments samplesall showed sigficanlty higher surface hardness and better wear resistance than the low carbonsteel substrate.In borate buffer solution, both the Fe-B alloy layer made by thermal expansionpenetrates and the compound deposited layer with boron-containing made byelectrodeposition performed better on the passivation than the low carbon steel substrate. Thepassivation film formed on the surface of the low-carbon steel was n-type semiconductor,which was the same as the Fe-B alloy layer sample and Fe-Ni/FeB compound deposition layer.And the majority carrier density in the film was electrons. However, passive film formed onthe surface of Ni-nano-B4C composite deposition layer performed p-type semiconductingcharacteristics, and the majority carrier was hole. The carrier density of the surfacepassivation film was also significantly lower than that on the surface of low carbon steel.Classic PDM mode was used to calculate the diffusion coefficient of the point defects for the deposited layer of the Fe-B alloy layer samples and the Ni-nano-B4C composite layer surfacepassivation film. The diffusion coefficient of the Fe-B alloy layer was10-17~10-14cm2/s, andthe Ni-nano-B4C composite sedimentary layer was10-14cm2/s. By using the quantitativeanalysis through the carrier density of the diffusion coefficient, it was determined that theelectro-conductibility of surface passivation film was mainly affected by the film carrierdensity.更多还原