Effects of pulse current on properties of electrodeposited RE-Ni-W-P-SiC composite coating

Effects of pulse current on properties of electrodeposited RE-Ni-W-P-SiC composite coating were studied. The results show that hardness of the pulse current electrodeposited composite coatings is higher than that of the direct current electrodeposited composite coatings while other parameters are the same. Otherwise, the deposited velocity is higher, and wear resistance and corrosion resistance of the pulse current electrodeposited composite coatings are also improved when the average current density is 10 A/dm2 , pulse frequency is 800 Hz and duty ratio is 1: 5. The hardness of the coating as-deposited is HV500 - 700, and it reaches HV1300 after heat treatment at 400 ℃ for 1 h.     

Study on Properties of Pulse Electrodeposited RE-Ni-W-P-SiC Composite Coatings

The effects of pulse frequency f and duty cycle r on the deposition rate, composition, morphology, and hardness of pulse electrodeposited RE （rare earth）-Ni-W-P-SiC composite coatings have been studied. The results indicate that pulse current can improve the deposition rate of RE-Ni-W-P-SiC composite coatings; W, P, and SiC contents in the coating decrease with the increase of pulse frequency and reach the lowest value at f = 33Hz, whereas the RE content in the composite coatings increases with the increase of pulse frequency. SiC content decreases with the increase of duty cycle, W content reaches the lowest value, and P content reaches the highest value at r = 0.4; pulse current and RE can lead to smaller size of the crystalline grains; however, the effects of different pulse frequency and duty cycle on the morphologies of RE-Ni-W-P-SiC composite coatings are not obvious. The hardness of RE-Ni-W-P-SiC composite coatings is the highest when the duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz. At the same pulse frequency, the hardness of RE-Ni-W-P-SiC composite coatings at r= 0.8 is higher than that at r= 0.6.     

脉冲换向电刷镀镍基纳米SiO2复合镀层的耐腐蚀性能研究

采用脉冲换向电刷镀方法制备了Ni/n-SiO2复合镀层,应用SEM对镀层表面形貌进行了分析,测试了镀层的孔隙率,以及镀层在海水浸泡条件下的耐腐蚀性能,讨论了镀层的耐腐蚀机理.实验结果表明:与直流工艺条件下的电刷镀镀层相比,脉冲换向电刷镀工艺得到的Ni/n-SiO2复合镀层具有致密精细的表面、较小的孔隙率和较高的耐腐蚀性能.     

占空比对氨基磺酸盐制备 Ni-TiN 纳米复合镀层性能的影响

目的进一步提高电沉积制备Ni-TiN纳米复合镀层的性能。方法选用氨基磺酸盐镀液体系,利用超声脉冲方法在3Cr13基体上电沉积Ni-TiN纳米复合镀层,研究占空比对纳米复合镀层TiN含量、表面形貌、显微硬度、微观结构的影响。结果随着占空比增加,镀层的硬度和纳米TiN含量先增加,后降低,镀层织构衍射强度增加,结晶度提高,衍射峰变窄。在占空比为0.2时,镀层TiN含量和硬度达到最大值,TiN质量分数为3.85%,硬度为580HV0.1,且镀层表面平整、致密。结论在一定的平均电流密度下,采用合适的占空比可以获得表面平整、致密的Ni-TiN纳米复合镀层。纳米TiN的共沉积影响了镍的结晶过程,不同占空比下制备的镀层中纳米TiN含量不同,引起了镀层晶格畸变,织构发生明显变化,性能改变。     

Effect of the plating parameters on the electrodeposition of Ni matrix coatings containing Ti nanoparticles

This work focuses on the production of electrodeposited nickel matrix composite coatings containing Ti nanoparticles and on the modification of the process parameters in order to maximise the codeposited particles content as well as obtaining a uniform distribution along the coating thickness. The deposition was carried out using a Ni sulphamate plating bath with different amounts of Ti nanoparticles. The plating parameters such as current density, current type (direct, DC, or pulsed, PC) and the use of ultrasound during the deposition have been modified. The specimens produced have had their microstructure, chemical composition and microhardness analysed. It was found that the increase of the particle concentration in the plating bath up to 40?g?L^?1 leads to an increase of the amount of codeposited particles. The use of ultrasound prevents agglomeration of the particles, leads to a more uniform distribution and increases the Ti content. However, it induces microstructural defects in the matrix. These defects can be limited by increasing the current density or by using pulsed current.     

脉冲偏压占空比对TiN/TiAlN多层薄膜微观结构和硬度的影响

目的研究脉冲偏压占空比对TiN/TiAlN多层薄膜微观结构和硬度的影响规律。方法利用脉冲偏压电弧离子镀的方法,改变脉冲偏压占空比,在M2高速钢表面制备5种TiN/TiAlN多层薄膜,对比研究了薄膜的微观结构、元素成分、相结构和硬度的变化规律。结果 TiN/TiAlN多层薄膜表面出现了电弧离子镀制备薄膜的典型生长形貌,随着脉冲偏压占空比的增加,薄膜表面的大颗粒数目明显减少。此外,脉冲偏压占空比的增加还引起多层薄膜中Al/Ti原子比的降低。结论 TiN/TiAlN多层薄膜主要以(111)晶面择优取向生长,此外还含有(311),(222)和(200)晶相结构。5种多层薄膜的纳米硬度均在33GPa以上,当脉冲偏压占空比为20%时,可实现超硬薄膜的制备。     

Corrosion protection of sintered NdFeB magnets by CAPVD Ti2N coating

Sintered NdFeB magnets have poor corrosion resistance and are readily susceptible to corrosion under different environmental conditions. Cathodic arc physical vapour deposited (CAPVD) titanium nitride coating for sintered NdFeB permanent magnets has been investigated in this paper. Tafel extrapolation was employed to study the corrosion behaviour in 3.5% NaCl solution at ambient temperature. The adhesive strength of the coating was estimated with the help of the scratch test. The surface chemistry and coating morphologies were studied with scanning electron microscope (SEM). X-Ray diffraction (XRD) was used for qualitative phase analyses of coatings and substrate. The properties of CAPVD titanium nitride coating were compared with electrodeposited multilayer nickel–copper–nickel coating. It was figured out that the CAPVD titanium nitride coating had better adhesion strength and shifted the free corrosion potential (FCP) of the system towards positive potential, providing protection to the NdFeB substrate. However, the corrosion rate of CAPVD titanium nitride coating was more than the electrodeposited multilayer nickel–copper–nickel coating. The magnetic properties remained comparable.     

HCPEB作用下镀铝CoCrAlY涂层的表面微观结构状态

采用大气等离子喷涂在GH4169镍基高温合金表面沉积CoCrAlY涂层,利用电子束蒸发镀膜技术在涂层表面沉积纳米铝膜,分别对镀铝前后的涂层使用强流脉冲电子束进行辐照处理,对处理前后的涂层表面进行成分及结构分析.XRD结果显示,经过HCPEB轰击之后,涂层表面纳米铝膜重熔,钴类氧化物消失,新增铝相,且随着轰击次数增加,β-CoAl含量增加.结构分析表明,电子束轰击可以使原始涂层表面尖角、孔洞、夹杂等消失,形成非常致密的凸起胞状体纳米超细晶结构,有利于抑制腐蚀性气体的侵入,同时铝含量的增加有利于抗氧化性能的提高.     

Influence of pulse plating parameters on morphology and hardness of pure tin deposit

Abstract

In the present work, the electrochemical deposition of tin coatings using pulse plating techniques was investigated. Based on fundamental electrochemical experiments, pure tin coatings were deposited by using direct and pulsed current. Both types of deposits were compared with each other and the effects of the pulse plating parameters, i.e. duty cycle, frequency and current density were investigated. Matt layers with wide powdery areas are obtained with direct current. At low current density and low duty cycle (10%), the pulsed current improves this aspect of the deposit by reducing the formation of powdery deposits. At higher duty cycles, the increase in the frequency additionally improves the hardness of the coating.     

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。     

Surface morphology and crystal orientation of electrodeposited tungsten coatings with different pulse parameters

This study was conducted to investigate the influence of pulse parameters on the surface morphology and crystal orientation of the tungsten coatings electrodeposited on pure copper substrates. The deposited coatings were analyzed by X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy-dispersive spectrometer(EDS). SEM analysis indicates that pulse parameters have significant influences on the surface morphology of the deposited coatings. Meanwhile, the change in grain size of the tungsten coatings demonstrates that the change in frequency and duty cycle could cause the variation of nucleation rate and grain growth of deposits.Moreover, no obvious diffusion layer at the coating/substrate interface is found by line analysis of EDS. XRD results reveal that tungsten coatings are of bcc structure and the preferred orientation of the deposits varies with duty cycle and period.     

Zn-Ni合金防腐涂层技术研究进展

Zn-Ni合金涂层技术是近年发展起来的防腐涂层新技术,与锌涂层相比,该涂层具有十分优异的腐蚀防护性能。随着工业的发展,Zn-Ni合金涂层将会成为锌的替代性涂层,在钢铁腐蚀防护领域得到广泛应用,极具发展前景。文中介绍了用电镀、热浸镀、热喷涂和渗镀的方法制备Zn-Ni合金涂层的主要进展情况,讨论了Zn-Ni合金涂层的腐蚀防护机理,指出了今后应把开发Zn-Ni合金基材作为Zn-Ni合金涂层技术获得突破的关键,把开发Zn-Ni复合涂层作为扩大Zn-Ni合金涂层应用的手段,同时应加强对Zn-Ni合金涂层耐腐蚀机理的研究,为Zn-Ni合金涂层技术的研究和应用提供理论指导。     

Characterisation of tungsten coatings by pulsed current plating from molten salt in air atmosphere

Pure and compact tungsten coatings with high (200)-orientation were successfully electrodeposited from Na₂WO₄–WO₃ binary oxide molten salt by direct and pulse current techniques on copper based alloy substrate in air atmosphere at 1173 K. The tungsten coatings and copper alloy substrates combined well with no obvious voids and cracks. In addition, the influence of pulse plating on the microstructure, crystal structure and Vickers microhardness of coatings, adhesive strength between coatings and substrates as well as the current efficiency was investigated. It was also observed that applied pulse current led to tungsten coatings with better mechanical properties than those obtained by direct current plating. In addition, a tungsten coating of 500 μm which had lower oxygen content and higher adhesive strength than the coating obtained by the plasma spray method was obtained.     

Effects of electric parameters on microstructure and properties of MAO coating fabricated on ZK60 Mg alloy in dual electrolyte

Micro-arc oxidation (MAO) process was carried out in a dual electrolyte system of NaAlO2 and Na3PO4 on ZK60 Mg alloys to explore the effect of electric parameters including current density, frequency, duty cycle and oxidation time on the evolution of coatings and other characteristics. The microstructural characteristics of coatings were observed by scanning electron microscopy (SEM) combined with the analysis of voltage-time responses during MAO process. Test of weight loss was conducted at a 3. 5％ NaCl solution to assess the resistance to corrosion. The results indicate that the current density and duty cycle play key roles on the coating quality. The peak voltage during MAO process increased with the increase in current density but the coating would be more easily detached when the current density was beyond a critical value. Voltage during MAO and microstructure of the coating were affected remarkably by duty cycle, and corrosion resistance was improved greatly when duty cycle was 40％. By means of single variable experiments, MAO process with optimized electric parameters was developed, which corresponds to the current density of 20 A·dm-2, frequency of 500 Hz, duty cycle of 40％ and oxidation time of 15 min.     

SiC颗粒尺寸对镍基复合镀层耐磨性和耐蚀性的影响

在正交实验基础上,对比研究微米SiC(平均粒径1.5 μm)和纳米SiC(平均粒径20 nm)增强复合镍基镀层的摩擦磨损行为和耐腐蚀性能.通过TEM、SEM、EDX和XRD等手段研究颗粒分散状态以及复合镀层的表面和截面形貌、成分及相结构.采用球-盘滑动摩擦磨损试验机研究复合镀层的耐磨性.电化学阻抗谱测量在3.5%的NaCl水溶液中进行.结果表明:微米级颗粒增强复合镀层可以获得更高的表面硬度,两种增强复合镀层具有相似的摩擦磨损行为.电化学阻抗谱分析表明:SiC颗粒的加入可以提高镀层的耐腐蚀性,且纳米颗粒复合镀层具有更好的耐蚀性.     

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。     

Corrosion behaviour of electrodeposited Ni/Al2O3 composite coating covered with a NaCl salt film at 800 °C

The electrodeposited Ni/Al₂O₃ composite coatings were prepared by direct current (DC), pulse current (PC) and pulse reversal current (PRC) deposition, respectively. The corrosion behaviour of electrodeposited Ni/Al₂O₃ composite coatings covered with NaCl salt films at 800 °C in air was investigated by SEM/EDX, XRD and thermogravimetric analysis. It is found that corrosion of the three types of coatings is seriously aggravated with a present NaCl salt film, and a corrosion layer with a poor adherence to the matrix has been formed. Furthermore, chlorine enrichment at the interface between the matrix and the corrosion product has been observed. The corrosion resistance of the three types of coatings has improved with the increase of Al₂O₃ content. The corrosion resistance of the Ni/Al₂O₃ composite coatings prepared by PRC deposition is the best, and that by DC deposition is the worst. The corrosion mechanism of Ni/Al₂O₃ composite coatings will also be discussed.     

Properties and structure of RE-Ni-W-P-SiC composite coating prepared by impulse electrodeposition

The properties and structure of electrodeposited RE （CeO2）-Ni-W-P-SiC composite coating were investigated. The results show that the hardness and electrodepositing speed of composite coatings obtained at an impulse current are higher than those at a direct current. The hardness and wear resistance of the coating are obviously increased by adding RE and SiC. The hardness of the coating increases with the increase of treatment temperature and current density, and reaches the optimum value at 400 ℃ and at 10 A/dm^2, respectively. The optimum operation parameters of electrodeposition of the composite coating are as follows： pH value is 4.5, bath temperature is 65 ℃, and current density is 10 A/dm^2.     

Ultrathin hydroxyapatite coating on pure magnesium substrate prepared by pulsed electron ablation technique

Magnesium (Mg) as a potential material for biodegradable implants is attractive due to its mechanical similarity to the bone tissue and nontoxic corrosion products. However, the rapid corrosion rate of bare magnesium is associated with hydrogen release, which may complicate the healing process. The corrosion rate may be reduced by suitable alloying, but concurrently the biocompatibility of such alloy might be deteriorated. Another way of reduction of the corrosion rate is coating. Hydroxyapatite (HA)-based coating is considered to improve biocompatibility as well as decrease the corrosion rate by the barrier effect. In this study, ultrathin (150 nm) HA and HA containing Sr coatings are deposited via pulsed electron ablation technique on pure Mg. The microstructure of the coating was assessed by scanning electron microscopy. Electrochemical methods were used to investigate the corrosion properties of prepared coatings. The materials covered by this layer were characterized by superior corrosion behavior, with corrosion rates of coated samples up to five times lower as compared with the uncoated ones. Such coating is the thinnest coating found in the literature sources.     

Effect of particle size and co-deposition technique on hardness and corrosion properties of Ni–Co/SiC composite coatings

Ni–Co/SiC alloy matrix composite coatings were electrodeposited in a modified Watt's bath containing micro and nano sized SiC particles by using conventional electro-co-deposition (CECD) and sediment co-deposition (SCD) techniques. The deposits were characterized using SEM, EDX and XRD analyses, and microhardness and potentiodynamic polarization measurements. The maximum incorporation of the SiC micro- and nano-particles was obtained using the SCD technique at deposition current densities of 2 and 3 A/dm², respectively. It was found that in the composite coatings, incorporation of SiC particles improves the microhardness of unalloyed Ni and Ni–Co alloy matrices. The nanocomposite coatings exhibit higher microhardness values than microcomposite ones. The potentiodynamic polarization measurements in 3.5% NaCl solution revealed that the corrosion resistance of the Ni–Co/SiC nanocomposite coatings is much higher than the Ni–Co alloy and Ni–Co/SiC microcomposite coatings. Moreover, corrosion resistance of Ni–Co/SiC nanocomposite coatings deposited by SCD technique is higher than the ones deposited by CECD technique. Corrosion resistance of the studied Ni–Co/SiC composite coatings was considerably affected by Co content, SiC particle size and content. Hardness enhancement was related to the structural features, and corrosion behavior was discussed based on the formation of corrosion micro cells, diminishing the effective metallic area, and increasing and hindering the corrosion paths.