【作者】 费敬银；

【导师】 梁国正；

【作者基本信息】 西北工业大学 ， 材料学， 2007， 博士

【摘要】 近年来，一种称之为组分调制多层膜的新型材料逐步成为人们研究的热点。组分调制多层膜是一类由两种金属或合金子层交替叠加而形成的多层结构材料。有研究结果表明，多层膜材料具有特殊的机械、力学、电磁学、光学和电化学性能。为了研制具有更好性能的新型防腐材料，已有人开始研究组分调制多层膜的耐腐蚀性能。初步研究结果表明，组分调制锌基多层膜材料具有更好的耐蚀性能。但是到目前为止，很少有人从机理上就组分调制多层膜耐蚀性能提高的原因给出合理的解释；组分调制合金多层膜的简易制备方法及其耐蚀行为的研究工作尚未广泛开展。因此，开展组分调制锌基多层膜的制备方法及其腐蚀行为研究，初步提出组分调制多层膜的耐蚀机理，从本质上揭示多层膜具有更高耐蚀性的本质，对探索组分调制锌基多层膜的结构与性能、制备新型耐蚀材料具有十分重要的理论及现实意义。为此，本文在全面分析、归纳、总结国内外组分调制多层膜制备方法及性能研究的基础上，从以下几个方面对组分调制锌基多层膜的制备方法及腐蚀行为进行了研究。1)采用双槽法从改进后的镀锌液和最新研制成功的近中性镀镍液中电沉积出了子层完整、界面清晰的组分调制Zn、Ni多层膜，并对多层膜的微观形貌、耐蚀行为进行了全面的研究。为了克服用氨基磺酸镍镀液电沉积镍子层过程中存在的问题，在制备组分调制Zn、Ni多层膜的过程中，本文提出了一种新型近中性镀镍溶液并对其电沉积特性进行了考察。研究发现，镀镍液性能的好坏、镀镍层内应力的大小是决定多层膜性能高低的关键因素。使用含有镍离子络合剂的近中性镀镍溶液有利于抑制电沉积镍子层时置换反应的发生，降低镍子层的内应力，从而可以制备出子层完整、界面清晰的多层膜。与相同厚度的纯锌、纯镍镀层相比，组分调制Zn、Ni多层膜具有更好的耐蚀性。当子层厚度为最佳厚度时，组分调制Zn、Ni多层膜具有最好的耐蚀性。在子层厚度相同的情况下，Ni／Zn系列多层膜比Zn／Ni系列多层膜具有更好的耐蚀性。多层膜腐蚀行为研究结果表明，锌子层的牺牲阳极保护作用，镍子层的机械隔离作用是组分调制Zn、Ni多层膜具有更好耐蚀性的根本原因。2)采用双槽法从改进后的镀锌液、优选出的Zn-Ni合金镀液中电沉积出了组分调制Zn、Zn-Ni合金多层膜，用现代表征方法研究了Zn、Zn-Ni合金多层膜微观形貌变化的规律及其耐蚀性提高的机理。在双槽法制备组分调制Zn、Zn-Ni合金多层膜及其耐蚀行为的过程中，首先对硫酸盐型Zn-Ni合金镀液的组成及工艺参数进行了优化，通过分析、归纳镀液组成、工艺参数对Zn-Ni合金镀层成份、微观形貌影响的规律，提出一种适用于制备组分调制Zn、Zn-Ni合金多层膜的Zn-Ni合金镀液配方。采用该配方电沉积出的组分调制Zn、Zn-Ni合金多层膜具有子层连续、界面分明等特点。Zn、ZnoNi合金多层膜的结构特征及其对多层膜耐蚀性能影响的规律与组分调制Zn、Ni多层膜相似。微观形貌表征结果表明，多层膜中Zn子层的存在有利于降低Zn-Ni合金子层的内应力，减少Zn-Ni合金子层中的微裂纹数，从而提高Zn-Ni合金子层对基体金属的保护作用。通过研究腐蚀后Zn、Zn-Ni合金多层膜微观形貌变化的规律发现，Zn-Ni／Zn系列多层膜比Zn／Zn-Ni合金系列多层膜具有更高耐蚀性的主要原因可能与Zn-Ni／Zn系列多层膜腐蚀过程中，在基体表面上残存有对基体起保护作用的Zn-Ni合金子层有关。3)利用含有逆向脉冲的脉冲电镀方法改变了Zn-Co合金直流电镀时固有的异常共沉积特性，实现了用脉冲参数控制法从单一槽液中电沉积子层成份任意可调的组分调制Zn-Co合金多层膜。用直流电沉积方法研究镀液组成、工艺条件对Zn-Co合金镀液电沉积特性影响的规律时发现，虽然Zn-Co合金镀液的组成、pH值、阴极电流密度、温度等均对Zn-Co合金镀层的成份、形貌产生一定程度的影响，但无法改变Zn-Co合金电沉积过程中的异常共沉积的特性，不可能用直流电沉积的方法获得含钴量较高的Zn-Co合金镀层。当采用含有逆向脉冲的脉冲电镀方法电沉积Zn-Co合金时，可以改变Zn-Co合金的异常共沉积特性。深入研究表明，所有脉冲参数均对Zn-Co合金镀层的组成、性能产生影响，其中逆向脉冲系数、平均电流密度对Zn-Co合金镀层的组成、形貌等影响最大，仅仅通过改变逆向脉冲系数、平均电流密度的值，就可以使Zn-Co合金镀层中的含钴量在10～90wt％的范围内发生变化。逆向脉冲的引入不仅改变了Zn-Co合金的异常共沉积特性，也对降低镀层应力、细化晶粒、制备高质量的Zn-Co合金镀层有积极作用。基于脉冲参数对Zn-Co合金镀层组成、性能影响规律研究的结果，利用计算机辅助电流波形设计技术，成功地制备了子层成份任意可调的组分调制Zn-Co合金多层膜。4)借助于中性盐雾腐蚀试验、腐蚀电位测量、阳极极化曲线测试、和腐蚀前后多层膜微观形貌、成份分析等手段，研究了多层膜的腐蚀机理。结果表明，尽管在不同类型多层膜中子层金属的种类各不相同，其保护基体金属免遭腐蚀的方式是相似的。多层膜中活性子层的牺牲阳极保护作用、惰性子层的机械隔离作用以及由它们共同产生的“协同效应”是其具有更好耐蚀性的根本原因。更多还原

【Abstract】 A new type of coating systems so-called compositionally modulated multilayerflims (CMMF) has been gradually gaining interest amongst researchers, because theselayered-structure coatings possess improved properties or novel phenomenon such asincreased mechanical strength, micro-hardness, giant magnetoresistance and corrosionresistance. CMMF consists of a large number of thin laminar deposits of metal or alloylayers, and each layer has its own distinctive role in achieving preferred performances.During last decades, the electrodeposition of zinc-based CMMF coatings for protectionof steel substrate from corrosion has been briefly investigated. To date, however,relatively few reports have given any evidences to "back-up" the enhanced corrosionresistance afforded by CMMF coatings. Therefore, further investigations are required toexamine the efficacy of this type of coatings on steel substrates and more convenientmethod are needed for the electrodeposition of zinc alloy CMMF coatings by usingsingle bath technique. The aim of the present work was to investigate the possibility ofelectrodepositing zinc-based CMMFs on steel substrate from the optimized electrolytesusing dual bath technique (DBT) and single bath technique (SBT), assess their corrosionperformance using mainly scanning electron microscopy (SEM), salt spray test,corrosion potential measurement and anodic polarization methods, and examine thecorrosion mechanism. The main results of the dissertation are as follows:1) Zinc and nickel CMMF coatings were produced by successive deposition from arevised zinc sulphate bath and a new developed nickel bath containing nickel-ammoniacomplexed electrolyte. The nickel bath has been particularly effective for the productionof zinc and nickel CMMF due to the low stress in the nickel deposits and less possibilityof a displacement reaction taking place with zinc surface due to the use of weaklyalkaline nickel bath. The surface and cross-sectional morphologies of zinc-nickelCMMF samples were examined using scanning electron microscopy (SEM).Zinc-nickel CMM coatings with uniform surface appearance could be obtained from these dual baths. A silvery grey colour was obtained with zinc as top layer and dullfinish with nickel as the top layer. Cross-sectional morphologies showed the layeredstructure was clear and no micro-cracks could be seen in the nickel sublayers. Corrosionresistance evaluated by means of neutral salt spray test showed that zinc-nickel CMMFcoatings were more corrosion-resistant than the monolithic coating of zinc or nickel ofsimilar thickness. Compared to the Zn/Ni CMMF coatings, Ni/Zn CMMF coatings withnickel sublayer adjacent to the steel substrate were more corrosion resistant, becausethere still was some nickel deposits remaining on the surface of substrate after corrosiontest, which would provide, to some extent, protection for steel. Results obtained fromcorrosion potential measurement and anodic polarisation suggest that pores and perhapsmicro-cracks existed in nickel sublayer which played an important role in achievingimproved corrosion resistance for zinc-nickel CMM coatings. Based on results fromelectrochemical measurement and the micrographic characteristics of zinc-nickelCMMF coatings after corrosion testing, a probable corrosion mechanism of zinc-nickelCMM coatings was proposed, the protection efficiency of zinc-nickel CMMF coatingsmay be thought to depend on the barrier effect of nickel sublayers and the sacrificialeffect of zinc sublayers. In reality, it may rely on producing the optimum protectionproperties of nickel sublayers.2) Prior to the production of Zinc and Zn-Ni alloy CMMF, the Zn-Ni alloy platingwas investigated to understand the effect of constituent and plating parameters of sulfateelectrolyte on the nickel content and surface morphologies of Zn-Ni alloy coatings. Thezinc and Zn-Ni alloy CMMF was electrodeposited from a revised zinc bath and theoptimized Zn-Ni alloy bath. Coated samples were evaluated in terms of surfaceappearance, surface and cross-sectional morphologies, as well as corrosion resistance.Microstructural characteristics examined using field emission gun scanning electronmicroscopy (FEGSEM), confirmed the layered structure, grain refinement of the zincand Zn-Ni alloy CMMF coatings, and revealed the existence of micro-cracks resultingfrom the internal stress in the thick Zn-Ni alloy sublayers. The internal stress of Zn-Nisublayer could be reduced to some extent by the electrodeposition of zinc sublayer. Thecorrosion resistance evaluated by means of salt spray test showed that the zinc and Zn-Ni alloy CMMF comings were more corrosion-resistant than the monolithic coatingsof zinc or Zn-Ni alloy alone of the same total thickness, and the Zn-Ni/Zn CMMFcoating system was more corrosion resistant than the Zn/Zn-Ni alloy system with asimilar configuration. Based on the analysis on the micrographic features of zinc andZn-Ni alloy CMMF coatings after corrosion test, the remaining coating material ofZn-Ni alloy deposit scattered on the steel substrate was the possible reasons why theZn-Ni/Zn CMMF coatings have a better protective performance.3) The electrodeposition of Zn-Co alloy was carried out using direct current (DC)electrodeposition method. Primary investigations indicated that it is difficult to getZn-Co alloy with high cobalt content because of the anomalous codeposition propertiesof Zn-Co alloy. The application of pulse current (PC) instead of DC was a suitableapproach to achieve Zn-Co alloys with a very wide range of alloy compositions andproperties by simply varying the applied pulse parameters. The results obtained fromthe investigation on the effect of pulse parameters on the cobalt content in Zn-Co alloydeposits showed that the cobalt content in the deposits depends mainly on the averagecurrent density and the value of the reverse pulse fraction. It is possible to electrodepositZn-Co alloy coatings with a very wide cobalt content range of 10-90 wt% bymodulating pulse parameters. The surface morphologies of Zn-Co alloy deposits wereexamined using scanning electron microscopy (SEM), and an attendant energydispersive X-ray analyser (EDA) was used to analyse the composition of Zn-Co alloydeposits. Grain size, surface appearance and internal stress in the deposits were alsoimproved significantly by introducing reverse current. Fine grain, more compact crystalstructures and crack-free Zn-Co alloy CMM coatings could be obtained by adjustingpulse plating parameters. By referring to the relationship of cobalt content and pulseparameters, a series of Zn-Co alloy CMMF coatings were produced using acomputer-aided pulse plater unit. The surface appearance, surface and cross-sectionalmorphologies of the Zn-Co alloy CMM coatings examined using FEGSEM, showedthat the production of Zn-Co CMM coatings is possible from a single bath bymodulating pulse current.4) The corrosion mechanism of CMMF was investigated using neutral salt spray corrosion test, corrosion potential measurement, anodic polarisation measurement, andmicrograph examination method. The probable reasons for the zinc-based CMMFcoatings to have much better protective performance were attributed to the sacrificialeffect of zinc sublayers and the barrier effect of noble metal sublayers, as well ascorporatively beneficial interaction.更多还原