The morphology and corrosion resistance of electrodeposited Co‐TiO2 nanocomposite coatings

Co‐TiO₂ nanocomposite coatings with various contents of TiO₂ nanoparticles were prepared by electrodeposition in Co sulfate plating bath containing TiO₂ nanoparticles. The influence of the TiO₂ nanoparticles concentration in the bath, of the current density and of sodium dodecyle sulfate (SDS) as anionic surfactant on the morphology, composition, texture, roughness, and microhardness of the coatings was investigated. The morphology and composition of coatings were studied by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The phase structure of coatings was analyzed by X‐ray diffraction (XRD). The results showed that the maximum codeposition of TiO₂ nanoparticles in Co matrix was around 4.5 vol% obtained in 60 g/L TiO₂ in the bath, 30 mA/cm² and 0.15 g/L SDS. The microhardness of coatings was increased up to 504 Hv by increasing TiO₂ concentration in the bath to 60 g/L TiO₂. The electrochemistry tests including potentiodynamic polarization and impedance spectroscopy revealed that by addition of TiO₂ into Co matrix, the corrosion current density, polarization resistance, and charge transfer resistance of Co‐TiO₂ coating were increased compared with Co coating.     

Influence of Pulse Electrodeposition and Heat Treatment on Microstructure,Tribological, and Corrosion Behavior of Nano-Grain Size Co-W Coatings

In the present study, Co-W nano-structured alloy coatings are produced on low-carbon steel substrate by means of pulse electrodeposition from a citrate-based bath under different average current densities and duty cycles. The results indicate that the coating deposited under 60% of duty cycle and 1 A/dm² of average current density exhibit optimum pulse plating conditions with 44.38 wt.% W, 37 nm grain size, and 758 HV microhardness. The effect of heat treatment temperature on microstructure, composition, corrosion behavior, and morphology of amorphous deposited Co-W alloy with 44 wt.% W was investigated. The microhardness of the coating increased to 1052 HV after heat treatment at 600 °C, which is due to the formation of Co₃W and CoWO₄ phases in the deposit. Furthermore, the coatings heat-treated at 600 °C had lower friction coefficients and better wear resistance under various loads than before heating.     

无氰电镀液中超声电沉积耐腐蚀纳米晶铜镀层

通过超声辅助电沉积法,在无氰络合电镀液中以高阴极电流密度在钕铁硼磁体上电沉积获得纳米晶铜防护镀层,研究了不同超声波频率下的镀层形貌、晶粒尺寸、显微硬度和耐腐蚀性能。结果表明,随着超声波频率的增加,络合电镀液体系的铜电沉积有效阴极电流密度显著增加,相应的阴极电流效率也提高,从而获得致密的纳米晶铜镀层。在阴极电流密度为4.0 A·dm^-2和超声波频率为40 kHz的条件下,能够获得平均晶粒尺寸为18.8 nm的铜镀层。超声辅助电沉积法还能促进烧结钕铁硼基体盲孔内的铜沉积,从而改善基体与镀层之间的结合力。在同样的镀层厚度下,烧结钕铁硼表面所沉积镀层的耐腐蚀性随超声波频率的提高而优化。     

The correlation among deposition parameters,structure and corrosion behaviour of ZnNi/nano-SiC composite coating deposited by pulsed and pulsed reverse current

The present work shows how the parameters of pulsed current (PC) deposition affect structural and morphological characteristics of electrodeposited ZnNi/nano-SiC composite coating and its corrosion properties. In this regard, ZnNi coatings containing SiC nanoparticles were electrodeposited from chloride bath by PC and pulsed reverse current (PRC) methods, and the effect of duty cycle, frequency and reverse current density were studied. With low and high duty cycles the SiC content of the coating was more than the coating deposited by medium duty cycle. Changing the duty cycle affected the coating composition, structure and morphology. Elevation of the pulse frequency increased SiC content of the coating. Application of PRC produced a coating with a complex and dendritic structure. In most of the electrodeposition conditions, in addition to direct effects of PC on coatings characteristics, it was seen that the more SiC was deposited in the coating the less Ni was deposited, and this also affected the corrosion behaviour. The best corrosion resistance behaviour was shown by coatings with more compact structure and less porosity.     

电沉积制备Ni/nano-WC复合镀层的工艺及机理研究

采用脉冲电沉积法制备了纳米WC强化镍基复合镀层。探究了不同表面活性剂（十二烷基硫酸钠）添加量以及WC粉的湿磨预处理对Ni/nano-WC复合镀层表面形貌、颗粒分布、微观结构以及显微硬度的影响。表面活性剂的添加和对WC湿磨处理有助于细化镀层晶粒,得到WC颗粒分布均匀的致密镀层。镀层中WC含量以及镀层的显微硬度随着表面活性剂的添加量的增加而增加,但过量会使效果变差,理想的SDS添加量为0.15g/l,湿磨10h。     

Ni-Co-CeO2镀层的制备及耐腐蚀性能研究

目的提高Ni-Co-CeO_2纳米复合镀层的显微硬度及耐腐蚀性能。方法利用超声技术,采用电沉积方法制备Ni-Co-CeO_2纳米复合镀层。通过正交实验方法,对Ni~(2+)、Co~(2+)及纳米颗粒共沉积工艺实验进行研究,以显微维氏硬度作为考察指标,通过极差分析确定电沉积的最佳工艺条件,利用极化曲线研究纳米复合镀层在3.5%NaC l水溶液中的耐腐蚀性能。通过XRD分析纳米复合镀层的相组成,采用SEM、EDAX研究纳米复合镀层的微观形貌和元素组成。结果通过超声场的超声空化作用,将纳米稀土CeO_2弥散分布于镀层中,使镀层晶粒细化,镀层硬度由264.34HV上升到486.82HV,同时镀层的耐蚀性能也有所提高,自腐蚀电流密度由6.305μA/cm~2减小至2.012μA/cm~2。结论由正交实验结果得出,在超声功率为160 W的实验条件下,制备镀层的最佳工艺条件为:镀液温度55℃,电流密度2 A/dm~2,纳米稀土CeO_2加入量1 g/L,pH值5。最佳工艺条件下制备的镀层表面致密均匀,硬度和耐腐蚀性均有明显提高。     

Effects of saccharin and cobalt concentration in electrolytic solution on microhardness of nanocrystalline Ni-Co alloys

Cobalt content, surface morphology and microhardness of nanocrystalline Ni-Co deposits prepared by pulse plating technique at constant electrodeposition conditions with varied concentration of saccharin and cobalt sulfate in the electrolyte were investigated. It is found that appropriate amount of both additions could lead to finer structure and higher hardness of the deposit and further increase of the concentration could result in decline of the hardness, which is regarded as the result of inverse Hall-Petch relation. The maximum hardness of the Ni-Co alloy deposits is not higher than that of their pure Ni counterparts, indicating that the refinement hardening effect (Hall-Petch relation) is dominant in nanocrystalline Ni-Co alloy deposits. By adding Co ions to the electrolyte, the amount of organic refiner saccharin (responsible for introduction of sulfur and carbon impurities) needed to produce nanocrystalline deposits could be remarkably reduced.     

Zinc–nickel alloy coatings electrodeposited from a chloride bath using direct and pulse current

Zinc–nickel alloys were electrodeposited on steel from chloride bath by direct and pulse current. Some electric variables (average current density, pulse frequency, duty cycle) and some important bath conditions (ratio of Ni²⁺/Zn²⁺ in bath, temperature) on chemical compositions, current efficiency, microhardness and surface appearance of coatings were studied. At low current densities, transition from anomalous to normal co-deposition was observed for both direct and pulse current. Pulse current seems to increase brightness of the coating and to decrease the precipitation of zinc hydroxide at the cathode surface. In addition, applied pulse current increases the percentage of nickel in deposits. Pulse frequency and duty cycle had little effect on the chemical composition of deposits. The polarization curve of zinc–nickel deposition with pulse current is shifted to positive potentials in comparison with direct current curves. The temperature of the plating bath had a very strong effect on the composition of the deposits. This is primarily the result of intrinsically slow nickel kinetics. The hardness of Zn–Ni alloy coatings (approx. 220 VHN) was greater than the hardness of zinc coating (approx. 161 VHN). The hydroxide suppression mechanism for Zn–Ni co-deposition has been confirmed.     

系泊缆用22MnCrNiMo钢表面纳米复合镀层的制备

目的制备性能良好的Ni-SiC复合镀层,以提高海洋平台系泊缆用22MnCrNiMo钢的耐腐蚀性和寿命。方法采用基于离心力的双脉冲电沉积技术,在海洋平台系泊缆用22MnCrNiMo钢表面制备Ni-SiC纳米复合镀层。通过扫描电子显微镜和光学显微镜对复合镀层的微观形貌、组织结构进行分析。利用静态浸泡腐蚀试验分析了镀层的耐腐蚀性能。结果添加0.2g/L的SDS时,纳米SiC悬浮液具有最佳悬浮性能。纳米SiC颗粒的质量浓度为2.0~4.0g/L时,有利于获得优异的Ni-SiC镀层表面形貌。随着占空比的增加,复合镀层表面的晶粒尺寸逐渐减小,当占空比为50%时,可以获得最佳的Ni-SiC镀层形貌。当添加2.0g/L的纳米SiC颗粒时,镀层的腐蚀质量损失最小,为2.867mg/cm~2;当占空比为50%时,镀层的腐蚀质量损失最小,为3.059mg/cm~2。结论添加分散剂后,镀液中的纳米SiC颗粒沉降性能变好;添加纳米SiC颗粒后,镀层的耐腐蚀性能增强。纳米SiC颗粒的添加量和占空比的大小对复合镀层的组织结构和耐腐蚀性能有重要影响。     

Influence of pulse parameters on electrocodeposition of Cr–Al2O3 nanocomposite coatings from trivalent chromium bath

Abstract

Cr and Cr–Al₂O₃ coatings were electrodeposited from Cr(III) bath with both pulsating and direct current onto copper substrates. Pulsating current resulted in homogeneous films of higher Al₂O₃ content and lower particle agglomeration than the direct current. Differences were more tangible at shorter duty cycles and pulse frequencies. Pulsating current improved both microhardness and corrosion resistance. The presence of alumina nanoparticles resulted in greater current efficiency, higher film microhardness and better corrosion resistance. Maximum current efficiency, highest microhardness and densest electrodeposited coatings were achieved at current density of 20 A dm^?2, duty cycle of 40% and pulse frequency of 10 Hz.     

超声条件下脉冲电镀 Ni-纳米 Al2 O3 复合镀层及其显微硬度研究

目的优选脉冲参数,以获得具有较高显微硬度的复合镀层。方法超声条件下,采用脉冲电镀方法制备Ni-纳米Al2O3复合镀层。以显微硬度作为性能指标,对比考察平均电流密度、占空比、频率和施镀时间的影响。结果 Ni-纳米Al2O3复合镀层的显微硬度随着平均电流密度升高,占空比增大,频率升高,均呈现出先增后减的趋势,而随着施镀时间延长,呈现出近似递减的趋势。结论在平均电流密度8 A/dm2、占空比0.6、频率1.5 k Hz、施镀时间3 min的条件下,制备的Ni-纳米Al2O3复合镀层显微硬度最高,约为427.1HV。较高复合量的纳米微粒有效起到了弥散强化和细晶强化作用,改善了复合镀层结构致密程度,进而提高了显微硬度。     

Microstructure and wear behaviour of pulse electrodeposited alumina nanoparticle reinforced Co–W nanocomposite coatings

Abstract

The microstructure and wear behaviour of alumina nanoparticle reinforced Co–W alloy coatings have been investigated for potential replacement of hard chrome coatings. The composite coatings were pulse electrodeposited on steel substrates using a citrate bath. The effects of current density, in the range of 1–9 A dm^?2, on the particle reinforcement, phase/microstructure, microhardness, and wear properties of the coating have been studied. The coatings codeposited with current density of 5 A dm^?2 at 333 Hz pulse frequency and 33% duty cycle exhibited microhardness comparable to hard chromium coatings.     

Preparation and characterization of nickel-cobalt-diamond electro-composites by sediment co-deposition

Nickel-diamond and nickel-cobalt diamond coatings were produced by electrodeposition using sedimentation technique on mild steel substrate and their tribological properties evaluated. Electrodeposition was carried out from a conventional Watts bath with cobalt addition. The conditions to obtain nickel-cobalt alloy were optimized first and then the conditions for obtaining diamond composites from both systems were investigated. Natural diamond powder of 6-12 μm size was used in the study. The volume percent incorporation of diamond powder in the coatings was investigated with respect to its concentration and cobalt concentration in bath, cathode current density, pH and temperature. The diamond powder distribution in the composite coatings, as examined with SEM, are uniform at low powder concentration in the bath and agglomerated at high concentrations. Physical properties of the composites including hardness, wear resistance and roughness were measured. Presence of cobalt increased volume percent incorporation of diamond powder, hardness and wear resistance of the coatings.     

Improving the corrosion and tribocorrosion resistance of Ni–Co nanocrystalline coatings in NaOH solution

Ni–Co nanocystalline coatings were electrodeposited from a modified Watts bath. Increasing the deposition current density had no significant effect on structure, corrosion and tribocorrosion behavior of the coatings. Adding saccharin into the bath reduced the grain size, increased the hardness, changed the texture component from (2 0 0) to (1 1 1), smoothed the surface morphology, increased the corrosion resistance and improved the tribocorrosion behavior of coating. Presence of sodium lauryl sulfate in the bath increased the corrosion resistance of coating by producing a more compact surface morphology. However, the coating showed low tribocorrosion resistance, probably due to its lower hardness.     

电沉积参数对Co-BN（六方、）纳米复合涂层显微组织和摩擦性能的影晌

通过扫描电镜、场发射扫描电镜、能谱、原子力显微镜和X射线衍射等测试技术,研究电流密度、占空比和频率对电沉积Co—BN（六方）纳米复合涂层的显微组织和BN粒子含量的影响。同时,研究其显微硬度、摩擦性能以及磨损机理。随着电流密度和频率的增加,涂层的BN粒子含量和显微硬度先增加后减少。另外,通过减少占空比,可以沉积更多的BN粒子并且得到更高的显微硬度。在占比空10％,频率50Hz和电流密度100mA／cm2的条件下,可以得到最佳的涂层摩擦性能。     

工艺参数对镍钴合金胎体摩擦磨损性能的影响

目的研究镀液中氨基磺酸钴浓度、电流密度及糖精钠含量对低钴镍钴合金镀层摩擦磨损性能的影响,提高耐磨性能,利于后续电镀用于航空材料孔系加工的金刚石刀具。方法在氨基磺酸盐镀液体系中,采用电沉积法制备低钴Ni-Co合金镀层。应用销盘式摩擦磨损试验机对镀层进行摩擦因数研究。采用三维形貌仪与LEICA DVM500显微镜观察镀层磨损宽度、深度与磨损形貌。分析不同电流密度、氨基磺酸钴浓度与糖精钠浓度对镀层摩擦因数、耐磨性能与磨损形貌的影响。结果当钴盐质量浓度从6g/L升至18g/L时,摩擦因素从2.273下降至1.915,提高了镀层表面平整性,降低了摩擦因数。随钴盐浓度提高,磨损形式从粘着磨损为主转为以磨粒磨损为主,镀层的抗塑性流变能力与耐磨性能得到提高。随电流密度升高,镀层平均摩擦因数从1.132增加至2.346,上升了107%,表面平整性下降,磨损横截面面积呈上升趋势,镀层的耐磨性能减弱,磨损机制转为粘着磨损和磨粒磨损双重磨损形式。糖精钠的加入使得摩擦因数从0.926上升至2.429,增加了1.6倍,但其磨损量下降明显,且磨损机制以磨粒磨损为主。结论提高钴盐浓度可细化晶粒,减小摩擦因数,提高镀层耐磨性,促进磨粒磨损发生。增大电流密度使得镀层晶粒粗大,致使摩擦因数升高,减小抗塑性变形能力,耐磨性能降低,促进粘着磨损发生。糖精钠有细晶作用,可缓解镀层磨损疲劳程度,提高其抗塑性流变能力,但对摩擦因数却起反向效果。综合,可选择电流密度2 A/dm2、钴盐质量浓度18 g/L及糖精钠质量浓度0.5 g/L作为工艺参数制备金刚石刀具胎体材料,由此获得的刀具具有较好的摩擦磨损性能,可提高使用寿命。     

Si3N4/Ni nanocomposite formed by electroplating:Effect of average size of nanoparticulates

Properties of Si3N4/Ni electroplated nanocomposite such as corrosion current density after long time immersion,roughness of obtained layer and distribution of nanometric particulates were studied.Other effective factors for fabrication of nanocomposite coatings were fixed for better studying the effect of the average size of nanoparticulates.The effects of the different average size of nanometric particulates(ASNP)from submicron scale(less than 1μm)to nanometric scale(less than 10 nm)were studied.The nanostructures of surfaces were examined by scanning electron microscopy(SEM),transmission electron microscopy(TEM)and atomic force microscopy(AFM).Corrosion rates of the coatings were determined using the Tafel polarization test.It is seen that decreasing the ASNP will lead to lower corrosion current densities;however,in some cases,pitting phenomena are observed.The roughness illustrates a minimum level while the distribution of nanometric particulates is more uniform by decreasing the ASNP.The effects of pulsed current on electrodeposition(frequency,duty cycle)and concentration of nanoparticulates in electrodeposition bath on trend of obtained curves have been discussed.Response surface methodology was applied for optimizing the effective operating conditions of coatings.The levels studied were frequency range between 1 000 and 9 000 Hz,duty cycle between 10%and 90%and concentration of nanoparticulates of 10-90 g/L.     

Synthesis and properties of electrodeposited Ni-CeO_2 nano-composite coatings

Current machinery requires metallic materials to have better surface properties. Based on an orthogonal experimental design and analysis method, the CeO_2-reinforced nickel nano-composite coatings were prepared by direct current electrodeposition in a nickel sulfate bath containing CeO_2 nanoparticles. Statistical results indicate that current density is the most significant variable in the electrodeposition processing, while temperature is the least important factor. The microstructure of Ni and Ni-CeO_2 nano-composite coatings was characterized by scanning electron microscopy(SEM) equipped with energy-dispersive spectroscopy(EDS), and X-ray diffraction(XRD).The microhardness of the Ni coating is enhanced by the incorporation of CeO_2 nanoparticles. Potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) were used to characterize the corrosion behavior of Ni and Ni-CeO_2 coatings. These studies show that NiCeO_2 coating has better corrosion resistance compared to Ni coating.     

占空比对高频脉冲电沉积( Ni-Co) / 纳米 Al2O3复合镀层的影响

采用高频脉冲电沉积法制备(Ni-Co)/纳米Al2O3复合镀层,研究了占空比对复合镀层沉积速率、成分、形貌及表面显微硬度的影响。结果表明:随着占空比由0.3提高至0.5,复合镀层的沉积速率增加,晶粒尺寸变大,表面变粗糙,并且Co含量降低,Ni含量增加,纳米Al2O3颗粒含量变化不明显,Co含量的降低导致硬度降低。     

Microstructure and properties of nanocrystalline nickel coatings prepared by pulse jet electrodeposition

The fabrication of nanocrystalline nickel coatings was conducted by pulse jet electrodeposition on the substrate of 45# carbon steel. The effects of average current density on the surface morphology, microstructure, average grain size and microhardness of nickel coatings were investigated by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and microhardness measurement. In addition, the corrosion resistances of coating and substrate were compared. It is revealed that the nickel coatings prepared by pulse jet electrodeposition exhibit a fine-grained structure with a smooth surface and a high density, although some pores and defects are still present in coatings. With the increase of average current density, the average grain size of nickel coatings is reduced at first and then increased. The coating with the optimum compactness, the smallest average grain size (13.7 nm) and the highest microhardness are obtained at current density of 39.8 A/dm2. The corrosion resistance is obviously increased for the coatings prepared by pulse jet electrodeposition; however, the corrosion rate is increased after a certain period due to the penetration of the corrosive media.