【作者】 谭澄宇；

【导师】 郑子樵；

【作者基本信息】 中南大学 ， 材料学， 2008， 博士

【摘要】 复合镀层可以改善材料的性能,满足不同用途的需求,在实际中获得了较为广泛的应用。利用复合沉积还可以制备一些特殊的复合材料。因此,复合电镀与制备工艺技术,复合镀层的性能以及相关机理一直成为研究的热点,引起了人们的普遍关注。本论文结合军工新材料科研项目对Ni-SiC、Ni-Al₂O₃、Cu-SiC以及Cu-ZrW₂O₈复合电沉积制备工艺进行了大量的试验,并对Ni-SiC复合镀层的耐磨性能、抗腐蚀性能等进行了测试与分析。论文还利用循环伏安、计时安培和交流阻抗等电化学研究方法深入探索粉体颗粒对金属沉积电结晶过程的影响,分析了金属与固体颗粒共沉积的复合机理。本论文共有九章。试验研究有六章篇幅,大体可分三个方面:第一部分研究与分析了复合电沉积相关基础理论;第二部分主要研究了镍基复合镀层,包括:Ni-SiC与Ni-纳米Al₂O₃复合沉积电化学基础、镍基复合电镀工艺以及Ni-SiC复合镀层的性能;第三部分主要研究了铜基复合镀层,包括:Cu-SiC复合电镀层制备工艺与电化学沉积基础;新型Cu-ZrW₂O₈复合镀层材料制备工艺等。1、复合电沉积相关基础理论研究论文第三章主要讨论了粉体的基本性质与其表面荷电的主要原因,提出了判断粉体表面荷电性质的方法;并利用镀液中pH值的变化,分析与表征了粉体在镀液中吸附离子,尤其是溶液中的氢离子形成表面电荷层的行为,粉体颗粒表面吸附金属离子是其嵌入镀层的重要原因。论文还借助开路电位讨论了镀液中粉体颗粒,镀液pH,温度、搅拌等因素对电极双电层的影响规律。依据Gugleilmi两步吸附机制关系式讨论了影响复合沉积的主要因素。初步研究结果如下:1)TiO₂,SiC,纳米Al₂O₃等粉体均能吸附镀液中的离子,吸附溶液氢离子引起镀液pH值发生变化。TiO₂在Watts镀液中PZC约为7.0左右,镀液pH＜7.0,粉体颗粒表面荷正电。粉体表面吸附溶液中离子的原因是,粉体表面非均质性与表面原子价键不饱和,表面晶格离子或表面官能团选择性溶解等因素所致。2)镀液中的粉体颗粒,镀液pH,温度、搅拌等因素均对电极双电层构成一定影响。从开路电位的变化来看,诸因素的影响大致在0.001～0.077 V范围,粉体的影响较大,其中以纳米粉体对电位的影响最大,可达0.077 V。3)依据Gugleilmi两步吸附机制,在一定的体系环境条件下,过电位（电流密度）与粉体复合含量具有指数关系,是影响复合沉积的重要因素。2、Ni-SiC复合电结晶行为研究论文第四章主要利用循环伏安、计时安培和交流阻抗研究Ni-SiC复合共沉积的电化学行为,探讨了微米级SiC颗粒对Ni电沉积结晶形核/生长模式以及电沉积还原反应过程的影响,利用扫描电镜观察了电结晶初期的形态。主要结论有如下几点:1)电化学试验表明:Ni-SiC镀液体系电沉积的起始电位约为-700mV;在较大阶跃电位下（-770～-830 mV）,Ni-SiC镀液体系电沉积基本满足Scharifker-Hills三维瞬时形核机制。随阶跃电位负移,Ni-SiC镀液体系电沉积结晶成核孕育时间逐渐缩短,且明显短于纯镍电结晶成核时间,反映SiC微粒在阴极表面能促进镍的电结晶成核;交流阻抗谱分析发现,SiC微粒能降低电沉积过程中的电荷转移电阻。但是,SiC微粒延迟沉积起峰电位,甚至降低电结晶峰值电流。2)扫描电镜观察发现:由于SiC粉体导电性差,致使其表面不易结晶成核,并且SiC粉体粘附在阴极表面上因遮掩而减少了有效阴极表面。因此推断,SiC微粒促使基质金属的电结晶成核归因于:粉体粘附在阴极表面扩大了吸附离子的实际表面,同时,镍离子放电相对集中,还原的吸附原子也相对富集的缘故。3、Ni-SiC复合电镀工艺与性能。论文第五章主要借助扫描电镜研究了电流密度、镀液pH值、粉体浓度与添加剂等工艺因素对镀层中粉体含量和复合镀层形貌的影响。大致确定了Ni-SiC复合镀层制备的优化工艺条件,分析了随沉积时间,镀层复合组织的演变特点。论文还就重力场,镀液的流动对复合镀层的形态影响进行了探索;尝试利用电镀工艺调控镀层微观组织,以改善复合镀层与基体之间的结合状况。论文还通过磨损减重、氧化增重、腐蚀失重等试验方法研究了Ni-SiC复合镀层的耐磨性能,高温抗氧化能力和耐3.5%NaCl盐水腐蚀等各项性能;利用极化曲线、交流阻抗谱分析了Ni-SiC复合镀层在3.5%NaCl+（H₂O₂）溶液体系中的腐蚀行为。主要结论如下:1)在Ni-SiC复合镀层制备过程中,随着电流密度的提高或镀液pH值的升高,复合镀层中SiC粉体含量呈峰值变化;在电流密度为3.3 A/dm²,镀液pH值3.8～3.9时,镀层中SiC粉体的含量较高。镀液中加入适量的添加剂能有效地提高镀层中SiC粉体的含量。2)随着镀层中SiC粉体含量的增加,复合镀层的显微硬度随之增大。通过分步施镀,调控电镀工艺,可以缓解厚镀层由于内应力过大而出现的镀层脱落现象,改善了复合镀层与基体之间的结合;显微硬度测试显示,利用分步施镀,还可实现Ni-SiC复合镀层的梯度化。3)在本试验条件下,Ni-SiC复合镀层的耐磨性、抗高温氧化性能均明显优于纯镍镀层。在3.5%NaCl溶液中,Ni-SiC复合镀层的腐蚀速率与纯镍镀层相当,随浸泡时间延长,复合镀层的腐蚀速率逐渐减小。添加少量双氧水后,Ni-SiC复合镀层与Ni镀层的开路电位明显正移,腐蚀电流减小,其耐蚀性能有所提高。4)阻抗谱分析表明,镍镀层在浸泡腐蚀初期表现为1个时间常数,随浸泡腐蚀时间,呈现出两个时间常数;而复合镀镍层的腐蚀过程只存在一个时间常数,这可能与复合镀层致密,孔隙被惰性微粒所封闭有关。4、Ni-纳米Al₂O₃复合制备工艺与电沉积行为纳米复合电沉积也是目前研究的一个热点,本论文第六章对纳米Al₂O₃的分散与Ni-纳米Al₂O₃镀液体系电沉积的工艺条件进行了探讨。同时利用循环伏安、计时安培和交流阻抗研究了Ni-纳米Al₂O₃镀液体系的电沉积行为,分析了在纳米Al₂O₃粉体影响下,镍电沉积结晶成核/生长的模式以及还原反应过程的特征。主要结论如下:1)随着阴极电流密度的增加或镀液pH的增大,复合镀层中的粉体含量有所降低,镀液温度在30～55℃范围对镀层中粉体含量影响较小,略呈峰值变化;在所采用的压缩空气和磁力搅拌方式中,适当地提高搅拌强度将有利于提高复合镀层中的粉体含量。2)电化学研究表明:Ni-纳米Al₂O₃镀液体系电沉积的起始电位约为-740 mV;Ni-纳米Al₂O₃镀液体系电沉积也满足三维生长模式的Scharifker-Hills模型;在较大阶跃电位-890 mV下,Ni-纳米Al₂O₃共沉积遵循瞬时形核机制。其成核孕育时间明显短于纯镍电结晶的成核时间,这说明纳米粉体在镀液中也将促进镍电结晶成核;但是,不同的是纳米Al₂O₃粉体并没像SiC微粒能显著降低沉积过程中的电荷转移电阻;此外,纳米粉体覆盖在阴极表面,同时也会减少有效阴极面积,延迟沉积起峰电位。3)扫描电镜观察发现,纳米粉体在复合镀层表面大致分布均匀,但存在小的团聚,基质金属层呈现出“蚕茧状”组织。5、Cu-SiC复合共沉积工艺与沉积基础研究。Cu-SiC复合镀层具有高强,耐磨,同时具有高热导,低膨胀系数等性能特点,在电子行业有着广阔的应用前景。论文第七章主要研究了Cu-SiC复合镀层制备的工艺条件以及SiC颗粒对铜电沉积结晶行为的影响。其主要试验结论如下:1)Cu-SiC复合沉积的初步试验表明:随着电流密度的增加,镀层中的SiC含量仅略有增大。在镀液中添加少量的添加剂,尤其是在低电流密度条件下将有利于提高镀层中粉体的含量;在低电流密度条件下（1 A/dm²）,SiC粉体在镀层中的含量可达14.07%wt。试验还发现:SiC粉体若先经NaOH溶液浸泡处理,能够有效提高镀层中粉体的复合含量。2)随镀层中SiC粉体的嵌入量增加,复合镀层的硬度明显提高;SiC粉体在镀层中含量为14.07%wt时,复合镀层硬度达206.98 Hv。3)循环伏安曲线与计时安培曲线表明,镀液中添加SiC粉体会阻碍铜的结晶沉积过程。在阶跃电位70 mV左右时,Cu-SiC镀液体系的电化学阻抗谱表现为一个略为压偏的半圆弧伴随在低频段出现感抗弧。随着过电位增加,弧半径逐渐减小。阻抗-电位曲线表明,在正电位约90 mV时,Cu-SiC镀液体系的阻抗值明显降低,反映铜结晶沉积开始发生。复合沉积过程仅对应一个时间常数。6、Cu-ZrW₂O₈新型复合镀层材料制备。论文第八章首先利用两步固相烧结法制备了钨酸锆粉体。在此基础上,尝试借助电沉积法制备高热导、低膨胀特殊复合材料Cu-ZrW₂O₈的工艺条件,并针对该方法的可行性进行分析与展望。主要结论如下:1)通过600℃+1170℃/24h烧结成功地制备了ZrW₂O₈粉体;本试验所采用的两步法合成工艺具有操作简便,合成粉体中ZrW₂O₈含量高的特点;2)在酸性镀铜液中成功地制备了Cu-ZrW₂O₈复合镀层,在电流密度2 A/dm²,镀液pH 1.1,温度25℃下电镀,铜镀层中ZrW₂O₈体积分数能达到～25%。随着电镀时间的延长,粉体在镀层中的含量略呈峰值变化;添加CTAB或CTAB+SDS将影响复合镀层的形貌,改善复合材料的平整性,但将降低复合镀层中的粉体含量。采用间歇式电镀方式可能有助于提高镀层中ZrW₂O₈粉体的复合含量。3)电沉积制备Cu-ZrW₂O₈复合材料是一个很有前途的方法。在10 A/dm²下,30小时长时间连续电镀,复合镀层厚度约为1 mm。对复合镀层截面观察表明,在镀层内、外表面附近分布着较多且较为粗大的粉体,而镀层中间部分,粉体含量较少且较细小,显现出不均匀的分布,因此,今后需要进一步提高粉体含量以及分布均匀性。更多还原

【Abstract】 The composite coatings can improve the properties of applied materials for various purposes and in the practice,have been wiedly used in different application field.The composite deposition tenicque can also be used to fabricate some special composite materials.Therefore,the researches about the plating technique,the properties and the deposition mechanics of the composite coatings are always hot-spots.The paper, based on the background of new material project for the war industry, abundantly studied the electro-deposition technique of Ni-SiC、Ni-Al₂O₃、Cu-SiC and Cu-ZrW₂O₈ composite coatings.The properties such as:the wear resistant,anti-high temperature oxidization and salt solution corrosion of Ni-SiC composite coating are measured and analysed in the paper.The influences of solid particles on the electro-crystallization process of metal deposition were also studied by using cyclic voltammetry,chronoamperometry and AC impedance spectra.The mechanics of metal co-deposition with solid particles were analysed in the paper.The paper has nine chapters in which six chapters relate to the experiment.All research work may be divided to three aspects:the first part mainly studied the basic theroies on the composition electro-deposition（see in chapter 3）.The second part studied nickel matrix composite coatings,including the electro-chemical fundament of Ni-SiC and Ni-nano-Al₂O₃ composite deposition,nickel matrix composite plating technology and the properties of Ni-SiC composite coating.The third part mainly studied copper matrix composite coating, including the fabricating technology for Cu-SiC composite coating,the electrochemical fundament for Cu-SiC composite deposition and the fabricating technology of new type Cu-ZrW₂O₈ composite material.1、Study on the fundamental theory of composite deposition In the third chapter,the solid powder feature and the primary factors of electrification on powder surfaces were discussed simply,and a method was given for determinating the positive or negative charge on powder particle surface.By pH change in bath solution,the chapter mainly analysed and described the behaviors of the electric double layer formatting on particle surface through powder adsorbing some positive ions,especially hydrogen ions in solution.Metal cation adsorbed on particle surfaces was thought as a very important factor for promoting solid particles into the coating.With measuring the open circut potential, the chapter also discussed the influence of some factors such as:solid particle in solution,bath solution temperature,pH and magnetic stirring et al on the electric double layer of the electrode surface.The main factors on the composite deposition were discussed according to two-step adsorbing mechanics of Gugleilmi.The preliminary results are shown as follows:1) Solid powders such as TiO₂,SiC,nano-Al₂O₃ particles etc can adsorb some ions in solution,especially hydrogen ion so as to cause the pH change in solution.PZC of TiO₂ powder in Watts` solution is 7.0 or so.When the solution pH＜7.0,the positive charge is inferred on the particle surface.The reasons on the powder surface adsorbing ions in solution are considered as the nonhomogeneous surface and the undersaturated valence bond of the atoms on surface.The other is also thought that the ions at surface lattice point or the functional groups on surface are selectly dissolved into the solution.2) Some factors such as:the powder feature and content in solution, solution temperature,pH,magnetic stiring etc have some influences on the electric double layer of the electrode.The effect range of various factors is about 0.001～0.077 V in open circuit potentials.The powder has more effect to the electrode potential,the most influence from among them is the nano powder,about 0.077 V。3) According to two-step adsorbing mechanics of Gugleilmi,the over potential（or current density） is a important factor to the composite deposition.Under certain circumstances,It is approximately exponential relation between the over-potential and the particle content in the coating.2、Electro-crystallization behaviors of Ni-SiC co-depositionThe chapter 4 in the paper studied the electrochemical behaviors of nickel co-deposition with SiC particles by using cyclic voltammetry, chronoamperometry and AC impedance spectra and explored the influences of SiC particles on electrochemical reaction and the nucleation/growth mechanics of nickel electro-deposition.The surface morphologies of Ni-SiC coating at the initial stage of the electro-crystallization were observed with Scanning Electron Microscopy（SEM）. The main results are shown as follows:1) Electrochemical tests show that nickel co-deposition with SiC particles may begin at applied potential -700 mV or so.Under higher over potential（applied potential:-770～830 mV）,the deposition nucleation of Ni-SiC solution system in the initial stage follows the instantaneous nucleation of Scharifker-Hills mechanism with three-dimensional.The nucleation time of Ni-SiC solution system may gradually be shortened with the increase of over potential and be more shorter than that of pure nickel deposition,which reflects that SiC particles on the electrode surface may offer many favorable sites for nickel crystallization nucleation.AC impedance spectra confirm that SiC particles can decrease electric-charge transfer resistance of nickel electro-deposition process. SiC particles may also results in that the peak current of Ni-SiC co-deposition descends and the potential corresponding peak current is also defered.2) The observation with SEM found that it is not easy to nucleate on particle surface because of SiC powder with poor electrical conductivity. In addition,SiC powders on cathode surface decrease the effective area for hydration cation reduction reaction.It can be inferred the reasons of the promoting effect of SiC powder to the electro crystallization nucleation of metal matrix are that SiC particles on the electrode surface may augment actual surface for adsorbing ions in bath solution and at the meantime,the hydration cation reduction reaction in the strictured cathode region increase the concentration of the reduction product （adsorbing atoms） so as to promote the electrocrystallization nucleation /growth.3、Plating technology and properties of Ni-SiC coatingThe chapter 5 in the paper mainly studied that the influence of technology factors such as:the current density,solution pH,solid particle concentration in solution and additive agent etc on SiC particle content in the coating and the morphology of the composite coating by using Scanning Electron Microscopy.Here offered the optimal process conditions for plating Ni-SiC coating and analyse the microstructure of the composite coating with plating time.The paper also discussed the influences of gravity and solution fluxion on the surface morphologies of the composite coating.By regulating plated-conditions and controlling the microstructure of the coating,the paper explored to improve the bonding condition of the interface between Ni-SiC composite coating and the cathode matrix.The chapter studied the wear resistant,anti-high temperature oxidization and the corrosion-resistant in 3.5%NaCl solution of Ni-SiC coating by means of abrading or corrosion loss weight and oxidization gain weight and analysed the corrosion behviors of Ni-SiC composite coating in 3.5%NaCl+（H₂O₂） solution with the polarization curve and AC impedance spectra.The main results are shown as follows:1) With the increase of current density or electrolyte solution pH value,SiC particle content in the composite coating exhibits a peak value change and under the conditions of current density 3.3 A/dm²,pH value 3.8～3.9,SiC content may be the maximum.Proper addition agent in bath solution can effectively promote SiC particle content in the composite coating.2) The micro-hardness of the composite coating increases with SiC content in the coating.Controlling technological parameter and using multiple-step plating may reduce the internal stress in the thick coating and improve the bond strength between the cathode matrix and the composite coating so as to avoid the desquamation phenomena（result from excessive internal stress）.Micro-hardness test implies that Ni-SiC composite material with gradient function may be fabricated by using multiple-step plating methode.3) Ni-SiC composite coating is superior in the wear resistance and anti- high temperature oxidation to pure nickel coating,and the corrosion resistance of Ni-SiC coating to 3.5%NaCl solution may be similar to that of pure nickel coating.With immersion time,the corrosion rate of Ni-SiC coating decrease gradually.The open circuit potential of Ni-SiC coating evidently moves to the positive direction and the corrosion current of Ni-SiC coating decreases after adding little H₂O₂ in 3.5%NaCl solution.4) EIS shows that at the intial stage of corrosion process there is only one time constant determined,and two time constants occur after prolonging immersion time,which may indicate that SiC particles improve the compactability of the composite coating（SiC particles obturate the hole in the coating）.4、Plating technology and behaviors of Ni-nanoAl₂O₃ co-deposition At present,metal co- deposition with nano-size particle also is one of research hot spots in the composite deposition field.The chapter 6 in the paper discussed the dispersion of nano-size Al₂O₃ powder in bath solution and technic conditions for Ni-Al₂O₃ co-deposition.The chapter also studied the electrochemical behaviors of Ni-nanoAl₂O₃ co-deposition by means of cyclic voltammetry,chronoamperometry and AC impedance spectra and analysed the reduction process feature and the mechanism of nickel electrocrystallisition from the bath solution containing nano-size Al₂O₃ particles.The main results are shown as follown:1) Al₂O₃ powder content in the coating decreases with cathode current density or bath solution pH.In the range of bath temperature: 30～55℃,the temperature has little influence on Al₂O₃ powder content in the coatings.Suitable stiring with compressed air or magnetic force may be benefit to improve the content.2) Nickel co-deposition with Al₂O₃ particles may begin at applied potential -740 mV or so and its nucleation also follows Scharifker-Hills with three-dimensional.Under the condition of higher over potential （applied potential:-890 mV）,Ni-Al₂O₃ co-deposition may meet instantaneous nucleation mechanism.The nucleation time of Ni-Al₂O₃ co-deposition also is shorter than that of pure nickel deposition,which indicates that Al₂O₃ particle offer favorable sites for nickel crystallization nucleation on electrode surface.In addition to,Al₂O₃ powder may also decrease virtual cathode surface and defere peak potential.But it is noteworthy that nano-Al₂O₃ powders do not apparently decrease Faraday resistance of nickel electro-deposition process,which distinguishs from the effect of SiC particles in co-deposition.3) The observation with SEM found that nano-Al₂O₃ powders are approximately homogeneous distribution in the coating except small quantity little agglomerated particles.The metal nickel matrix of Ni-Al₂O₃ coating represents a kind of"podlike" microstructure.5、Technology and fundament of Cu-SiC co-depositionOwing to have good properties such as:higher strength,wear resistant,at the meantime,good thermal conductivity and low expansion coefficient etc,Cu-SiC coating has wide application and good prospect in electronic industry.The chapter 7 mainly studied the technic conditions for fabricating Cu-SiC composite material and the influence of SiC particle on the behaviors of copper electro-crystallization.The results are shown as follows:1) The experiment shows that with the current density,SiC particles in the coating just increase a little and adding suitable addition agent （especially at low current density） may be good to promote SiC powder content in the coating.Under the low current density of 1 A/dm²,the content is 14.07%wt or so.It is also found that SiC powder soaked in NaOH solution can effectively promote SiC powder content in the coating.2) The hardness of the composite coating increases evidently with the content of SiC powder in the coating.When SiC particle content in coating is 14.07%wt or so,the hardness reaches 206.98 Hv。3) The cyclic voltammetry and chronoamperometry show that SiC powder in bath solution may inhibit copper electro-crystallization process. Under the step potential of 70 mV or so,the electrochemical impedance spectra of Cu-SiC system represent a depressed semicircle following an inductive reactance arc in low frequency section.With the increase of over-potential,the radius of the semicircle decreases gradually and the impedance value of Cu-SiC system descends evidencely.The impedance-potential curve indicates that the electro-crystallization deposition may occur at the potential 90 mV or so.Only one time constant emerges during the deposition process.6、Fabricating Cu-ZrW₂O₈ composite materialIn the chapter 8,Zirconium tungstate powder was fabricated by using two-step solid state sintering method and the co-deposition technic conditions for fabricating Cu-ZrW₂O₈ composite material with high thermal conductivity and low expansion coefficient were preliminarily studied in the test.In the end,the paper discussed the practicability and development trend of the composite materials fabricating by using electron-deposition methode.The main conclusions are shown as follows:1) ZrW₂O₈ powder was successfully synthesized by using 600℃+1170℃/24h sintering method.Two-step sintering process is simple for operation in practice and ZrW₂O₈ content is high in sintered powder.2) Cu-ZrW₂O₈ composite coating has been successfully prepared from acid electrolyte.Under the condition of current density 2 A/dm²,pH 1.1,solution temperature,25℃,ZrW₂O₈ content in the coating is about～25%vol.The content exhibits a little peak change with the plating time. Adding CTAB（cetyltrimethyl ammonium bromide） or CTAB+SDS （lauryl sodium sulfate） agent in bath solution can influence the surface morphologies and the smoothness of the composite coatings,and decrease zirconium tungstate particle content in the composite coating. The operating with the intermittent-plating fasion may be favorable to increase ZrW₂O₈ content in the coating.3) The electro-deposition method has good prospect for fabricating Cu-ZrW₂O₈ composite material.The thickness of the composite coating reachs to 1mm or so after plated at the current density of 10 A/dm² for 30 hours.The observation from the cross-ssection of the composite coating found that ZrW₂O₈ powder is inhomogeneous distribution in the coating. There are many coarse powder in the coating near to the inner or external surface,but a small amount minor ZrW₂O₈ particles is in the middle range of the coating.Therefore,it needs to further improve the powder content and uniformity in the future.更多还原