阴极等离子电解沉积技术简介及其研究进展

阴极等离子电解沉积是一种将传统电解和等离子体相结合的表面处理与材料制备技术,与传统的表面处理技术相比,该技术在能量消耗、制备速率、沉积层表面致密度、与基体结合力等方面均有大幅度改善,因此备受关注。概述了阴极等离子电解沉积的基本机理,包括电压-电流的演变过程、气体鞘层的形成过程、等离子体的演变规律和金属离子的沉积现象等,在此基础上讲解了阴极等离子电解沉积的技术优势。针对阴极等离子电解沉积过程中复杂的影响因素,分析并探讨了电压、占空比、时间等电参数以及酸含量、添加剂、电解液浓度等溶液参数对阴极等离子电解沉积的影响规律。在此基础上,重点综述了近年来阴极等离子电解沉积在多个领域的研究进展,包括先进陶瓷涂层、金属涂层以及复合涂层的制备,纳米电催化剂、纳米微球、中空微球和石墨烯等功能材料的合成以及渗碳、渗氮等领域的应用等。最后总结并展望了阴极等离子电解沉积在涂层领域的发展方向以及催化剂、石墨烯等其他新型领域的研究前景。     

等离子体电解阴极沉积Y2O3陶瓷涂层

在Y（NO3）3水溶液中,以Fe25Cr5Al合金为阴极,研究了等离子体电解阴极沉积Y2O3陶瓷涂层的规律。研究发现,当施加的槽电压超过临界值时,阴极发生气膜微弧放电,在合金表面沉积出Y2O3陶瓷涂层。研究了施加槽电压、沉积时间、Y（NO3）3浓度对沉积Y2O3陶瓷涂层的影响。扫描电镜（SEM）、X射线衍射（XRD）分析结果表明,获得的Y2O3陶瓷涂层表面具有熔融的特征,涂层致密与基体结合牢固。探讨了等离子体电解阴极沉积Y2O3涂层的机理。     

阴极等离子电解沉积Ni-P和Ni-P-ZrO_2纳米晶涂层

采用电极移动液流式阴极等离子电解在304不锈钢基体上沉积Ni-P和Ni-P-Zr O2纳米晶涂层。结果表明,提高溶液中Zr O2纳米颗粒的浓度可以降低起弧电压,对Ni-P-Zr O2涂层的成分、结构和性能有着显著的影响。SEM形貌观察表明,阴极等离子电解沉积的Ni-P和Ni-P-Zr O2涂层具有熔融后快速凝固的特征,涂层与基体具有冶金结合。根据XRD的衍射峰宽的计算结果证明这些涂层具有纳米晶粒结构。元素分析结果证明,提高溶液中Zr O2纳米颗粒的浓度,可以提高镀层中弥散Zr O2颗粒的含量,但会降低P的含量。硬度和磨损实验结果表明,Ni-P涂层中弥散纳米Zr O2后,可显著提高涂层的显微硬度和耐磨性能。     

阴极等离子电解大面积沉积涂层技术

阴极等离子电解沉积技术是一种先进的涂层制备技术。利用此技术制备的涂层往往具有新的结构和性能,如涂层的纳米结构、与基体的冶金结合、优异的耐常温腐蚀性能和抗高温氧化性能,并能实现水溶液中难以还原的活泼金属的沉积以及在难熔合金上直接进行沉积等。但是,由于沉积过程中气膜微弧放电的不均匀性,人们难以通过阴极等离子电解沉积在大面积试样上获得均匀、致密的涂层。近年来,北京市腐蚀、磨蚀与表面技术重点实验室课题组致力于阴极等离子电解大面积沉积金属、合金及陶瓷涂层的研究,并取得了较大的进展。阴极等离子电解沉积技术作为一种绿色环保的工程技术,阴极等离子电解沉积将具有广阔的应用前景。     

阴极等离子电解制备抗氧化涂层

目的 通过对阴极等离子电解放电机制进行讨论,提出大面积沉积复杂形状试样的解决办法.方法 在电解液中添加表面活性剂和氯铂酸制备Pt颗粒弥散的复合涂层,通过测试电流密度-电压曲线,分析气膜放电机制,通过扫描电子显微镜对涂层的表面、截面形貌进行分析表征.结果 在电解液中添加表面活性剂或者在阴极区施加微珠,使气膜层更均匀,同时降低了沉积涂层的电流密度.随着Pt含量的增加,涂层孔隙率逐渐降低.涂层中弥散的Pt颗粒起到了弥散增韧的作用,提高了涂层的断裂韧性和抗剥落性能.结论 实现了在大面积复杂形状试样上制备陶瓷涂层,并通过在涂层中弥散Pt颗粒提高了涂层的致密性.     

阴极等离子电解沉积Ni和Ni-Al_2O_3纳米涂层

采用电极移动液流式阴极等离子电解在304不锈钢基体上沉积Ni和Ni-Al2O3纳米涂层,研究了溶液组成和电参数对Ni和Ni-Al2O3涂层结构和性能的影响。涂层形貌观察表明,阴极等离子电解沉积的Ni和Ni-Al2O3涂层具有熔融后快速凝固的特征,涂层与基体具有冶金结合。根据XRD的衍射峰宽计算了涂层的晶粒尺寸,结果表明制备的涂层具有纳米结构。元素分析结果证明,Ni-Al2O3涂层中含有少量的纳米Al2O3颗粒,且表面的Al2O3含量比涂层中高。纳米Al2O3颗粒弥散在Ni中显著提高了涂层的显微硬度和耐磨性能。     

钢表面电火花沉积合成W-Mo高熔点复合涂层

目的 采用ZY-10型电火花堆焊/涂层沉积设备,分别以钼和钨棒料为电极,以超纯氩气为保护气体,在PCrNi3MoVA钢基体表面沉积合成W-Mo高熔点复合涂层。方法 在PCrNi3MoVA钢基体表面先沉积出一定厚度的钼涂层作为打底层,在此基础上,采用更高的电参数沉积硬度和熔点都较高的钨涂层。作为同族元素的钼和钨,在高温电弧作用下能较好地合成W-Mo高熔点复合涂层。通过对复合涂层的成分、微观形貌等进行观察和分析,用等离子烧蚀实验检测复合涂层的抗烧蚀性能,并计算复合涂层的质量烧蚀率和线烧蚀率。结果 采用电火花沉积工艺在PCrNi3MoVA钢基体表面成功制备了W-Mo高熔点复合涂层,其厚度达到100 μm以上,该复合涂层主要由W、Mo、Fe等成分组成,且越靠近涂层表面,W和Mo元素的含量越高,复合涂层主要有Mo、MoC、Fe2Mo3、Fe2W等物相,复合涂层的耐烧蚀性能较好,在前10 s内其线烧蚀率仅为0.090~0.267 mm/s。结论 W-Mo高熔点复合涂层的厚度随着沉积次数和沉积电压的增加而增加;复合涂层与基体相互熔融,具有较好的冶金结合特征;复合涂层能够承受等离子火焰的短时高温冲击与冲刷,增加复合涂层的厚度可以有效抑制涂层试样烧蚀率的增加。     

硬质合金刀具ZrC涂层的沉积

采用原位卤化反应直接形成的ZrCl4气体作为Zr源,在硬质合金刀具上沉积CVD-ZrC涂层。用SEM,XRD分析检测了合金刀具基底不同表面上沉积生长ZrC涂层的厚度均匀性、沉积速率、形貌组织、织构取向;通过理论计算与工艺实际的涂层沉积转化率对比,定量表征了该沉积体系工艺参数下ZrC涂层的沉积转化率。结果显示,CVD涂层炉内不同位置合金刀片表面沉积的ZrC涂层均匀;由于工艺温度限制,涂层沉积速率较低;ZrCl4转化为ZrC涂层的工艺实际转化率约11%,在理论最大转化率14%范围内;相同温度下随着沉积压力升高,涂层的沉积转化率缓慢降低到10%并趋于稳定;直接在合金基底沉积形成的ZrC涂层为细小的颗粒状形貌,而在合金基底TiN涂层表面上沉积生长的ZrC具有典型的片状组织形貌;对应的涂层生长织构取向从(311)到(111)转变。     

豪泽公司研发第二代HIPIMS＋涂层技术

物理气相沉积（PVD）涂层工艺主要是通过电弧蒸发作用或磁控溅射作用来实现涂层在刀具表面的沉积。荷兰的PVD和等离子体辅助CVD涂层技术开发商——豪泽技术涂层公司（Hauzer Techno Coating BV）正在尝试用其第二代高能激发磁控溅射（HIPIMS＋）涂层技术对PVD涂层工艺进行创新变革。     

梯度成分结构TiAlSiYN涂层的制备及其抗氧化性能研究

目的采用阴极电弧镀叠加磁控溅射的复合PVD涂层技术,实现梯度成分结构Ti AlSiYN多元涂层的制备。方法在涂层沉积过程中,通过切换不同成分的电弧靶,获得成分梯度变化的Ti AlSiYN涂层。利用扫描电子显微镜及其附带能谱仪、X射线衍射仪分析涂层氧化前后的截面组织形貌、成分和物相结构。结果在阴极电弧沉积过程中,通过磁控溅射方式植入微量Y元素会干扰涂层的生长,降低涂层的生长速率。Y元素在涂层中具有细化柱状组织的作用,并使涂层的开始氧化温度和氧化速率降低。相比于均一成分结构的Ti AlSiN涂层,均一成分结构的Ti AlSiYN涂层在800℃时表层未发生氧化。在900℃保温1 h后,Ti AlSiYN涂层的高氧含量氮氧化物层厚度小于Ti AlSiN涂层。梯度成分结构使Ti AlSiYN涂层的抗氧化性能明显降低,在900℃保温1 h后,梯度成分结构的Ti AlSiYN涂层组织完全被氧化,氧化组织以金红石结构的Ti O2为主,还有少量锐钛矿结构的Ti O2、Si O2和Al2O3。结论微量稀土Y元素具有改善涂层抗氧化性的作用,而梯度成分结构不利于涂层的抗氧化性。     

The properties of electrodeposited Zn-Co coatings

The possibility of increasing the corrosion resistance of automotive sheet steel by electrodepositing with Zn-Co alloy coatings was investigated. Process variables during electrodeposition such as current density, electrolyte flow rate, and pH were varied in order to examine their influence on the electroplating process. Cobalt contents varying from 0.2 to 7 wt% were easily obtained. The influence of these process parameters on the characteristics of the coating could be related to the hydroxide suppression mechanism for anomalous codeposition. The structure and the morphology of the coatings were determined using SEM and XRD analysis. Application properties important for coating systems used in the automotive industry, such as friction behavior, adhesion, and corrosion behavior, were investigated on coatings with varying cobalt content. The corrosion resistance of the Zn-Co alloy layers was found to be better than that of pure zinc coatings.     

Residual stresses in thick, nonhomogeneous coatings

Residual macrostresses in thick, nonhomogeneous planar coatings are investigated theoretically using the methods of the isotropic theory of elasticity. The dependence of the elastic properties and of the sources of residual stresses on the coordinate perpendicular to the interface is considered. The results can be applied to thick graded or sandwich coatings. A simplification of the results for the cases of homogeneous and thin coatings is shown. Some differences for coatings on cylindrical and spherical surfaces are also mentioned.     

An analysis of the cold spray process and its coatings

In this study, computational fluid dynamics (CFD) and extensive spray tests were performed for detailed analyses of the cold spray process. The modeling of the gas and particle flow field for different nozzle geometries and process parameters in correlation with the results of the experiments reveal that adhesion only occurs when the powder particles exceed a critical impact velocity that is specific to the spray material. For spherical copper powder with low oxygen content, the critical velocity was determined to be about 570 m/s. With nitrogen as the process gas and particle grain sizes from 5–25 μm, deposition efficiencies of more than 70% were achieved. The cold sprayed coatings show negligible porosity and oxygen contents comparable to the initial powder feedstock. Therefore, properties such as the electrical conductivity at room temperature correspond to those of the bulk material. The methods presented here can also be applied to develop strategies for cold spraying of other materials such as zinc, stainless steel, or nickel-based super-alloys.     

Combined pre-annealing and pre-oxidation treatment for the processing of thermal barrier coatings on NiCoCrAlY bond coatings

A combined pre-annealing and pre-oxidation treatment was developed for the processing of partially yttria stabilized (PYSZ) thermal barrier coatings (TBC) on top of NiCoCrAlY bond coatings (BC). To develop this pre-treatment, the influence of the oxygen potential during pre-annealing and pre-oxidation on the life span and failure mechanisms of the entire high temperature coating system upon thermal cycling was investigated. The results of this study showed that the service life of the coating system depended strongly on the composition and microstructure of the thermally grown oxide (TGO) after pre-oxidation. The longer life spans were obtained if the TGO thickened very slowly during thermal cycling due to a large α-Al₂O₃ grain size. Such a slow-growing TGO corresponded with a pre-treatment for which θ-Al₂O₃ was formed during pre-oxidation and for which the yttrium was located within a high density of pegs along the TGO/BC interface after pre-oxidation. If the yttrium was present on top of the TGO after pre-oxidation, a thick mixed alumina-zirconia layer formed upon thermal cycling. This mixed oxide layer contributed significantly to the total oxide layer thickness, resulting in short life spans. The formation of NiAl₂O₄ spinel in between the TBC and the α-Al₂O₃ should be avoided, since this can lead to premature failure along the spinel/α-Al₂O₃ interface.     

Development of multimaterial coatings by cold spray and gas detonation spraying

The basic objective is the development of multifunctional multimaterial protective coatings using cold spraying (CS) and computer controlled detonation spraying (CCDS).As far as CS is concerned, the separate injection of each powder into different zones of the carrier gas stream is applied. Cu-Al, Cu-SiC, Al-Al₂O₃, Cu-Al₂O₃, Al-SiC, Al-Ti and Ti-SiC coatings are successfully sprayed. As to CCDS, powders are sprayed with a recently developed apparatus that is characterized by a high-precision gas supply system and a fine-dosed twin powder feeding system. Computer control provides a flexible programmed readjustment of the detonation gases energy impact on powder thus allowing selecting the optimal for each component spraying parameters to form composite and multilayered coatings. Several powders are sprayed to obtain composite coatings, specifically, among others, WC-Co-Cr + Al₂O₃, Cu + Al₂O₃, and Al₂O₃ + ZrO₂.     

Ambient and high-temperature thermal conductivity of thermal sprayed coatings

Aside from its importance as a design parameter for thermal barrier coatings, measuring thermal conductivity of thermal sprayed coatings itself provides a unique method to critically characterize the nature, quantity, and anisotropy of the defect morphologies in these splat-based coatings. In this paper, the authors present a systematic assessment of thermal conductivity of wide range using the flash diffusivity technique. For the case of plasma sprayed yttria-stabilized zirconia (YSZ), coatings obtained from wide-ranging initial powder morphologies as well as those fabricated under different particle states were characterized. Both in-plane and through-thickness properties were obtained. Other material systems that were considered include: metallic alloys and semiconductors of interests. Issues such as reproducibility and reliability in measurements were also considered and assessed. Finally, work in collaboration with the Oak Ridge National Laboratory (ORNL) for alternate approaches to characterization of thermal conductivity as well as high-temperature measurements was performed. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Manufacture and properties of composite coatings: An introduction

Composite layers are capable of varying surface properties of parts over wide ranges. The galvanic route and thermal spraying are predestined to create composite layers. Wear resistance can be realized by a metallic matrix and nonmetallic reinforcing component that serves as a disperse phase. The goal of this article is to report on experimental results gained from samples produced galvanically. Improved wear resistance and hardness of the composite layers are main topics. The thermal spray process requires more sophisticated processing techniques if the desired components cannot be supplied by individual injectors or mechanically premixed. In cases where pneumatic material feed (e.g., carbon short fibers) is not possible, the material supply must be achieved by agglomerated powders containing the second phase as a constituent. Suitable agglomerated powders allow a control of thermal decomposition of the sprayed materials by using additives as admixture to the agglomerate. Practical examples are outlined in the article.     

Structure and properties of cathodic vacuum arc deposited NbN and NbN-based multi-component and multi-layer coatings

Binary Nb-N coatings, ternary Ti-Nb-N and Zr-Nb-N, and multi-layer TiN/NbN coatings consisting of up to 100 alternating TiN and NbN layers, were deposited onto WC-Co substrates, using two different vacuum arc deposition (VAD) systems: with and without magnetic guiding of the metal plasma flow. Binary Nb-N coatings were fabricated by deposition of metal plasma produced by a Nb cathode in a background of reactive nitrogen gas at different pressures, P. Ternary coatings were fabricated at co-deposition of plasmas originating from two different cathode materials. Multilayer coatings were fabricated by alternatively depositing plasmas of Ti and Nb in reactive nitrogen gas. The crystalline coating structure, phase composition, hardness and critical load for coating failure were studied.For binary Nb-N coatings fabricated using both deposition systems, the phase composition, the Vickers hardness, HV, and the critical load strongly depended on the deposition pressure. Using VAD with magnetic plasma guiding, the highest HV of ∼ 42 GPa was measured for coatings deposited at low nitrogen pressure. These coatings contained a hexagonal β-Nb₂N phase and had a relatively low critical load. The highest critical load and HV ∼ 38 GPa were obtained for coatings consisted of a single phase NaCl-type cubic δ-NbN structure, deposited at a higher nitrogen pressure. The structure and properties of Nb-N coatings deposited using VAD without magnetic plasma guiding had a similar correlation with the deposition pressure, however, their hardness values were lower.Ternary Ti-Nb-N and Zr-Nb-N coatings fabricated by both deposition processes had a single phase cubic NaCl-type structure and the hardness higher than that of the binary nitrides TiN, ZrN and NbN. The hardest coatings, HV ∼ 51.5 Pa, deposited with magnetic plasma guiding had a single-phase cubic δ-(Ti,Nb)N structure and a Ti:Nb ratio of ∼ 50:50 (at.%).Multilayer coatings TiN/NbN consisting of 20-40 alternating TiN and NbN layers with total thickness of 4-5 μm increased the life time of cemented carbide cutting inserts at turning tough Ni-base alloys by 2-7 times relative to uncoated cutting tools, while conventional vacuum arc deposited TiN coatings were not effective in machining of these alloys.     

Laser-assisted spraying and laser treatment of thermally sprayed coatings

In the present study, surface engineering research related to thermally sprayed wear and corrosion resistant coatings modified by in-situ and post-treatment by novel high power lasers (Nd:YAG and diode lasers) has been carried out. The main aim of the study was to create experimental based information and knowledge on simultaneous remelting of thermally sprayed (plasma, HVOF, flame) single layers for production of metallurgically bonded, dense corrosion and wear resistant coatings on surfaces of steels. The main focus of research was to estimate the needed processing parameters, which enable simultaneous laser-assisted thermal spraying. The microstructures and hardness-profiles for the coatings prepared by laser-assisted thermal spraying are also introduced.     

纳米结构涂层与纳米改性材料

简要介绍作者近年来研发的几项纳米结构涂层和纳米改性材料技术的研究与应用进展,包括热喷涂纳米结构陶瓷涂层、热喷涂纳米结构硫化物自润滑涂层、电镀和电泳沉积纳米结构涂层、纳米改性硬质合金材料、纳米改性合金铸铁材料。从而证明纳米科技的工业应用不是梦。