Microstructure and electromagnetic interference shielding effectiveness of electroless Ni–P plated polyester fabric

Microstructure and electromagnetic interference shielding effectiveness of electroless Ni–P deposits obtained from an alkaline hypophosphite reducing electroless nickel bath was studied. The effects of plating temperature on the deposition rate, surface morphology, chemical composition and structure of the electroless Ni–P deposits were investigated. Surface resistance and electromagnetic interference (EMI) shielding effectiveness (SE) of Ni–P plated polyester fabric were also evaluated. The results demonstrated electroless Ni–P plated polyester fabric present useful EMI shielding materials.     

Electroless deposition of Ni–P–B4C composite coating on AZ91D magnesium alloy and investigation on its wear and corrosion resistance

In the present work, the effect of applying ternary Ni–P–B₄C composite coating from an electroless plating bath containing sulfate nickel, sodium hypophosphate and suspended B₄C particles, on the corrosion and wear resistance of an AZ91D, high aluminum cast magnesium alloy, was investigated. Regarding low corrosion resistance of magnesium alloys, chromium oxide plus HF (Hydro Fluoric Acid) pretreatment was applied to prepare the substrate for coating treatment in electroless bath. The pH value and temperature of the electroless bath were 9 and 82 °C, respectively. The coating was characterized for its micro structure, morphology, microhardness, wear and corrosion resistance. SEM (Scanning Electron Microscope) observation showed dense and coarse nodules in the ternary composite coating and the cross section of Ni–P–B₄C coating offered presence of well dispersed B₄C particles in the coating. The hardness of the Ni–P–B₄C composite coatings was around 1200 MPa, more than what can be obtained for Ni–P coatings (about 700 MPa). The wear test which was carried out by using pin on disc method, showed that ternary Ni–P–B₄C composite coating had a good wear resistance and more superior than Ni-P coating. The polarization test results for ternary Ni–P–B₄C composite coating exhibited good corrosion resistance properties in protecting the AZ91D magnesium alloy, but not better than Ni–P coating.     

Study on thermal stability of electroless deposited Ni-Co-P alloy thin film

The Ni–P and Ni-Co-P alloy thin films were deposited on silicon substrates with electroless technique. The solid state metallurgical reactions were investigated with silicon for the viewpoint of Co co-deposition effect. The alloy film kept amorphous state with increasing Co content even though the P content decreased. The films become more amorphous, and the thermal stability increased with increment of Co content in the deposit. The Co content was varied from 11.013 to 45.068 wt% while P content was decreased from 9.340 to 6.491 wt% by varying the concentration of components in electroless deposition baths. The thermal stability was examined by X-ray diffractometer (XRD), four probe, and atomic force microscopy (AFM). The results indicated the Ni-Co-P alloy films with lower P content show the higher thermal stability then the ordinary Ni–P films and prevent the silicidation at low temperature because the Ni crystallization formation suppressed by the co-deposition of Co.     

Investigation on a Non-cyanide Plating Process of Ni-P Coating on Magnesium Alloy AZ91D

In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coating on Mg alloy AZ91D, the process of copper transition coating plated in the cyanides bath can be replaced. A new bath composed of NiSO4 was established by orthogonal test. The results show that zinc transition coating can increase the adhesion and pH 4.0 and 95℃, respectively. The present process flow is composed of ultrasonic cleaning→alkaline cleaning→acid pickling→activation→double immersing zinc→electroplating zinc→electroless nickel plating→passivation treatment.The present non-cyanide process of electroless nickel plating is harmless to our surroundings and Ni-P coating on Mg alloy AZ91D produced by present process possesses good adhesion and corrosion resistance.     

全光亮化学镀镍磷合金工艺研究

研究出了一种新型不含铅的全光亮化学镀镍工艺,获得了全光亮的镍磷合金镀层.通过试验分析镀液中添加剂、无机盐、主盐、施镀时间、pH值和施镀温度对化学镀镍磷合金层光亮度的影响;检测了有关性能.结果表明:所得化学镀镍磷合金镀层的光亮度、耐蚀性等性能优于常规化学镀镍磷合金镀层.CuSO4、TaSO4无机盐的添加使溶液稳定性(氯化钯稳定试验)从30 s提高到90 s,同时也提高了化学镀镍磷合金镀层耐蚀性,在5%NaCl溶液中的年腐蚀量从1.1 mg/cm2降为0.     

Tribology of electroless nickel coatings – A review

Electroless coating is different from the conventional electrolytic coating as the former does not require any electricity for its operation. The advantages include uniform coating and also nonconductive materials can be coated. Electroless nickel coatings possess splendid tribological properties such as high hardness, good wear resistance and corrosion resistance. For this reason, electroless nickel has found wide applications in aerospace, automobile, electrical and chemical industries. Quest for improved tribological performances has led many researchers to develop and investigate newer variants of electroless nickel coatings like Ni–W–P, Ni–Cu–P, Ni–P–SiC, Ni–P–TiO₂, and so on. Also the enhancement of tribological characteristics through modification of the coating process parameters has remained a key point of interest in researchers. The technological advancement demands the development of newer coating materials with improved resistance against wear and tear. Electroless nickel has shown huge potential to fit in that space and so the study of its tribological advancement deserves a thorough and exhaustive study. The present article reviews mainly the tribological advancement of different electroless nickel coatings based on the bath types, structure and also the tribo testing parameters in recent years.     

铝及铝合金全光亮化学镀镍磷合金工艺优选

化学镀镶前的预处理对镀层性能非常重要,目前常用的预处理方法存在许多缺陷.为此,通过对各种预处理工艺的筛选,确定了适用于铭合金化学镀镍磷合金的条件预处理工艺并预镀中间层,然后在传统化学镀镶磷镀液中加入镀镍中间体和无机盐,组合出了一种新的全光亮化学镀镍磷合金工艺,探讨了镍液主要成分和工艺条件对沉积速度、镀层耐蚀性和外观质量...     

Effect of heat treatment on age hardening behaviour of electroless nickel–phosphorus coatings

Abstract

Electroless nickel–phosphorus (EN) coatings have been widely used in various industries such as oil, gas, electronic, chemical, automotive, aerospace, and mining. The EN coating process is based on a redox reaction in which a reducing agent is oxidised and Ni²⁺ ions are reduced on the substrate materials. Once the first layer of Ni is deposited, it acts as a catalyst for the process. Consequently, a linear relation between coating thickness and time usually occurs. If the reducing agent is sodium hypophosphite, the deposit obtained will be a nickel–phosphorus alloy. Also, the actual nickel and phosphorous levels in the EN deposit depend on the composition, temperature, and pH of the plating bath used. In this work, three types of EN coatings have been studied: low, medium, and high phosphorus Ni–P alloys. The techniques used were: differential scanning calorimetry (DSC), SEM, and hardness measurements. Heat treatment resulted in precipitation of nickel phosphides, e.g. Ni₃P, and nickel crystallites. Thus, the phosphorus content of the coating was reduced. The results of isochronal age hardening showed that the peak age hardening temperature for the three EN coatings occurred at ～673 K. However, the time to reach peak hardness during isothermal heat treatment at 593 K varied with phosphorus content. Also, it was found that the temperatures at which peak precipitation reactions occur during DSC scan are influenced by phosphorus content.     

聚丙烯塑料低温化学镀Ni-P工艺的研究

研究了Ni-P化学镀液的主要成分、pH值和温度工艺参数对化学沉积Ni-P合金镀层镀速的影响.通过选择合适的镀液成分和工艺参数,在PP塑料基体上低温化学镀Ni-P合金工艺中获得中磷含量合金镀层,探讨了镀液组分对镀层性能的影响,优化了工艺参数.利用扫描电镜测得镀层的含磷量为8.057%,所以为非晶态的镀层.     

镁合金硫酸镍体系化学镀镍工艺及镀层性能研究

采用酸性钼酸盐酸洗、碱性钼酸盐活化工艺,研究了AM60镁合金上硫酸镍溶液体系化学镀镍的方法.采用扫描电子显微镜(SEM)观察镀层表面形貌,电子探针(EDX)分析镀层成分,电化学方法研究镀层腐蚀性能,锉刀试验测试镀层与基体结合力.结果表明,所得镀层为Ni-P合金镀层,磷质量分数为10%～14%;镀层均匀致密,无明显缺陷;镀层的自腐蚀电位接近-0.4 V(vs SCE),阳极极化曲线有明显的钝化区;Ni-P镀层耐蚀性好,与基体结合牢固.     

化学沉积Ni-Mo-P合金工艺参数对性能的影响

研究了镀液pH值和温度等工艺参数对化学镀Ni Mo P合金镀层耐蚀性和硬度的影响。试验结果表明 ,镀液 pH值升高 ,镀层的沉积速度和硬度升高 ,而耐蚀性下降 ;镀液温度升高 ,镀层的沉积速度升高     

Corrosion resistance enhancement of Ni–P electroless coatings by incorporation of nano-SiO2 particles

Composite coatings were prepared using hypophosphite reduced electroless nickel bath containing 7 g/L SiO₂ nano-particles at pH 4.6 ± 0.2 and temperature 90 ± 2 °C. Deposition rate for SiO₂ nano-composite coatings was 10–12 μm/h. The amount of SiO₂ nano-particles co-deposited in the Ni–P matrix was around 2 wt.%. The analyzes of coating compositions, carried out by Energy Dispersive Analysis of X-ray (EDAX), showed that plain Ni–P and Ni–P/nano-SiO₂ deposits contained around 8 wt.% phosphorus. The X-ray diffraction (XRD) pattern of Ni–P/nano-SiO₂ coating was very similar to that of plain electroless Ni–P coating, whose structure was also amorphous.     

Study of nanometer Al2O3 composite electroless deposit strengthened by different laser power

Featured by cheap equipment, easy operation, nice controllability and low consumption, compound electroless deposit becomes an effective method to avoid failures such as high-temperature corrosion, fatigue and abrasion. Combined with the merits of nanometer material and laser treatment technology, the Ni–P nanometer Al₂O₃ electroless deposit after laser strengthening can get finer grains with high performances. This paper researched the technique of laser strengthening on 3Cr13 stainless steel after Ni–P–nano-Al₂O₃ electroless plating. The experiments with low laser power and high laser power were performed. The crystallinity, phases and element distribution of coating were analyzed by X-ray diffraction (XRD) and energy spectrometer (EDS). The microhardness and wear resistance of coating were measured as well. The results showed that composite coating heated by low laser power leads to transformation from non-crystal to crystal with high hardness. When heated by high laser power, the electroless deposit layer melted, and most of amorphous transformed to crystal. Combined with high laser power and high scanning velocity, the electroless deposit with finer grains and excellent properties was obtained. The strengthening mechanism was analyzed, and the properties including hardening and wear resistance were investigated as well.     

Influence of the anionic part of the stabilizer on electroless nickel-boron plating

Selectivity and smooth operation of electroless nickel plating require that a stabilizing agent is used. It operates by blocking catalytic activity on unwanted germination sites and regulating the activity of the substrate. In the case of alkaline electroless nickel-boron plating systems, which use sodium (or potassium) borohydride as reducing agent, lead and thallium salts are the most popular stabilizers. However, there is little knowledge about the way the stabilizer acts. In this study, 4 different lead-based stabilizers (tungstate, sulphate, nitrate and chloride) have been used, all other things left constant, in electroless nickel-boron plating baths. The thickness, composition, roughness, morphology, hardness and structure of all the obtained coatings have been investigated. Chloride led to thinner deposits and the boron content varied between 5.5?wt.% for lead tungstate and 6.5?wt.% for lead nitrate and lead sulphate, with a lead content between 0.2 and 0.25?wt.%. Coatings obtained with a lead tungstate stabilized bath were thicker, harder and contained less boron and lead than the others. This shows the influence of the anionic part of the stabilizing agent on the plating process.     

Protective coating for magnesium alloy

A phosphate–permanganate conversion coating was applied as the pretreatment process for AZ91D magnesium alloy substrate. Zn–Ni alloys were electrodeposited onto the treated AZ91D magnesium alloy from sulfate bath. The morphology and phase composition of the coatings were determined with X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The results reveal that the conversion rate depends on pH of solution and treatment time. Salt spray and the electrochemical polarization testing were applied to evaluate the corrosion performance of phosphate–permanganate and Zn–Ni coated alloys. It was found that Ni content in deposit is a function of current density and bath composition. Zn–13 wt.% Ni coating provides very good corrosion protective function to inner AZ91D magnesium alloy. Phosphate–permanganate treatment enhances the corrosion resistance of Zn–Ni coatings.     

NdFeB磁体表面化学镀Ni-Co-p合金及其耐腐蚀性能研究

采用化学镀方法制备Ni-Co-P三元合金镀层以改善NdFeB磁体的耐腐蚀性能.优化了镀液配方以及施镀工艺,研究了镀液pH值和金属离子配比([Co2 ]/[Ni2 Co2 ])对沉积速度和镀层成分的影响,测量了NdFeB基体和不同镀层在3.5%(质量分数,下同)NaCl溶液中的极化曲线.结果表明,随镀液pH值增加,沉积速度提高,镀层中Co含量升高,Ni含量和P含量逐渐降低;随镀液中Co2 比例增加,沉积速度下降,镀层中Co含量升高,Ni和P含量降低.化学镀Ni-Co-P合金后的NdFeB磁体在3.5%NaCl溶液中的腐蚀速度降低了约两个数量级;当镀液金属离子配比[Co2 ]/[Ni2 Co2 ]=0.3时,镀层耐腐蚀性能最好,且优于相同施镀条件下所得到的Ni-P镀层.     

环保型镁合金化学镀镍工艺研究

研究了镁合金的环保型化学镀镍工艺,对前处理工艺进行了简化,对镀液的稳定性、循环使用后的节约成本核算以及废液的回收处理等进行了研究和探讨.结果表明,使用一步前处理工艺能简化镁合金前处理工艺,提高镀镍层的结合强度和质量,且处理液中不含Cr6 、HF等对环境和人体有害的物质;化学镀液的循环使用可以大幅度节约生产成本,减少废液排放,提高资源的利用率.     

An investigation on corrosion resistance of as-applied and heat treated Ni–P/nanoSiC coatings

EN–SiC coatings are recognized for their hardness and wear resistance. In this work electroless Ni–P coatings containing nano SiC particles were co-deposited on St37 tool steel substrate. Scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray diffraction (XRD), polarization and electrochemical impedance spectroscopy (EIS) were used to analyze morphology, structure and corrosion resistance of the coatings. The results showed that SiC nano-particles co-deposited homogeneously, and the structure of Ni–P–SiC nano-composite coatings as deposited was amorphous. Heat-treatment at 400 °C for 1 h induced crystallization of the electroless Ni–P coatings. Microhardness of electroless Ni–P–SiC composite coatings increased due to the existence of nano-particles, and reached to a maximum value after heat-treatment. Corrosion tests showed that both electroless nickel and electroless nickel composite coatings demonstrated significant improvement of corrosion resistance in salty atmosphere. Proper post heat-treatment significantly improved the coating density and structure, giving rise to enhanced corrosion resistance.     

An Analysis of Fiber-Induced Surface Defects in Electroless Plated Components

The paper discusses the analysis of a coating defect on a high phosphorus electroless nickel (Ni-11 wt. % P) deposit plated on an aluminum alloy substrate. Preliminary investigations had indicated that the elongated defects were possibly caused by the entrapment of long fibers or particles during the plating. The possible sources of fibers were identified. The SEM/EDS analysis of fibers collected from the air duct filters correlated very well with the defect shape and the EDS profile collected from under the defect site. It appears that the fibers from air duct filters directly above the plating line were blown into the plating tank and getting co-deposited. The paper describes the step-by-step analysis of the defect that led to successful identification of the root cause of the defect.     

Interfacial reactions between Sn-3.5 Ag solder and Ni–W alloy films

Nickel based alloys are currently being investigated in an effort to develop stable barrier films between lead free solder and copper substrate. In this study, interfacial reactions between Ni–W alloy films and Sn-3.5 Ag solder have been investigated. Ni–W alloys films with tungsten content in the range of 5.0–18.0 at.% were prepared on copper substrate by electrodeposition in ammonia citrate bath. Solder joints were prepared on the Ni–W coated substrate at a reflow temperature of 250 °C. The solder joint interface was investigated by Cross-sectional scanning electron microscopy, energy dispersive X-ray spectroscopy and electron back scatter diffraction. It has been observed that a Ni₃Sn₄ layer with faceted morphology formed on the Ni–W alloy film after reflow. The thickness of the bright layer was found to decrease with the increase of tungsten content in the Ni–W film. An additional layer with a bright appearance was also found to form below the Ni₃Sn₄ layer. The bright layer was identified to be a ternary phase containing Sn, W and Ni. The bright layer is found to be amorphous and is suggested to have formed through solid state amorphization caused by anomalously fast diffusion of Sn into Ni–W film.