The effect of SiC particles added in electroless Ni-P plating solution on the properties of composite coatings

To verify the relationship between the properties of composite coatings prepared on Q235 steel and the SiC content of electroless Ni-P-SiC composite coatings, systematic experiments with varied SiC contents and surfactants have been conducted. The experimental results indicated the approximate linear relation between the SiC content and the hardness of composite coatings. With the increasing of SiC content, wear resistance increases correspondingly. In particular, the effect of SiC content on the corrosion resistance of Ni-P-SiC composite coatings immersed in different corrosive solutions (i.e. 5% H₂SO₄, 20% NaOH and 3.5% NaCl) is explored, followed by a comparative analysis of the corrosion resistance between Ni-P and Ni-P-SiC coatings. Corrosion test indicates that NaOH solution makes no differences in the corrosion resistance between Ni-P coatings and electroless Ni-P-SiC composite coatings, both being uncorroded. Exposed to NaCl solution, the corrosion resistance of electroless Ni-P-SiC composite coatings decreases gradually with the increasing of SiC content in coatings. In H₂SO₄ solution, the corrosion resistance of coatings increases initially and decreases afterwards with the sustained increasing of SiC content in coatings, and the optimized corrosion resistance is obtained at a SiC content of 9.41 wt.%. Finally, a competent electroless Ni-P-SiC composite plating process producing a high wear resistance and sound corrosion resistance of the coatings is obtained.     

氧化铝含量对Ni-P化学复合镀层摩擦学性能的影响

采用化学镀技术制备了不同氧化铝含量的Ni-P复合镀层,并用球盘式磨损试验机测试了镀层的摩擦磨损性能。利用扫描电镜、光学显微镜和X射线衍射仪对镀层和对偶球的表面形貌、成分及微观结构进行了表征,分析了镀层的磨损机理。结果表明：镀层中氧化铝质量分数最高可达34.7%,但镀层磷含量显著降低,Ni-P合金基体为无定形结构;镀层的摩擦因数(约为0.49～0.58)高于Ni-P合金,且随着氧化铝含量的增加先降低后增加,镀层的维氏硬度从502上升至764,磨损率从1.2×10_-14 m₃/(Nm)单调下降至3.2×10_-15 m₃/(Nm),镀层的主要磨损机理由粘着磨损逐步转变为磨粒磨损。     

A new method for electroless Ni-P plating on AZ31 magnesium alloy

Coating Ni-P films on AZ31 magnesium alloys via electroless plating and organic coatings (organsilicon heat-resisting varnish), was studied. An organic coating was proposed as the interlayer between Ni-P coating and AZ31magnesium alloy substrate, to replace the traditional chromium oxide plus HF pretreatment. The Ni-P deposited on the interlayer was also characterized by its structure, morphology and corrosion-resistance. The interlayer on the substrate not only reduces the corrosion of magnesium during Ni-P plating process, but also reduces the potential difference between the matrix and the second phase. The result of the cross-cut test indicates the adhesion between the substrate and the interlayer is good enough. A Ni-P film with fine and dense structure was obtained on the AZ31 magnesium alloy. The electrochemical measurements show that the sample with Ni-P film exhibits lower corrosion current density and more positive corrosion potential than the substrate. Furthermore, the Ni-P coating on the AZ31 magnesium alloy exhibits high corrosion resistance in the rapid corrosion test illustrated in this paper. The method proposed in this work is environmentally friendly: no fluoride or hexacalent chromium compounds are used. In addition, it provides a new concept for plating the metals, which are considered difficult to plate due to high reactivity.     

A study of corrosion resistance and formation characteristics of electroless Ni-P alloy coatings on Al18B4O33w/6061 Al composite with a simple surface pre-treatment

Ni-P alloy coatings were successfully deposited on Al₁₈B₄O₃₃w/6061 Al composite by electroless deposition. A simple surface pre-treatment method prior to the coating process was used for the first time. The coatings were characterized by SEM/EDX, TEM and electrochemical methods. It was found that the pre-treatment prior to the coatings had an important effect on the electroless plating, which offered an active surface for the electroless deposition, resulting in the Ni-P coatings being uniformly formed on the substrate and providing the protection for the composite substrate.     

Electroless deposition of Ni-P composite coatings containing kaolin nanoparticles

Abstract

The ability to codeposit particulate matter in a matrix of electroless nickel has led to a new generation of composite coatings with unique properties, such as high hardness wear, abrasion, corrosion and high temperature oxidation resistance. In this paper, the authors report on the development of electroless Ni–P–kaolin composite coating, and the characteristic properties of the selected deposits were evaluated by scanning electron microscopy, energy dispersive X-ray and X-ray diffraction techniques. A good rate of deposition of 12 μm h^?1 was observed for the optimised concentration of 6 g L^?1 of kaolin in the bath. For the optimised bath composition and operating conditions, the composite deposit was found to contain 81·7%Ni, 9·8%P and 10·5%kaolin. Heat treatment at 400°C for 1 h results in an increase in the hardness and wear resistance of the composite coating. The corrosion resistance is also highly enhanced by the incorporation of kaolin in the nickel–phosphorus matrix. The crystallite size of the composite coating is 20 nm, and the codeposition of kaolin follows the Langmuir adsorption isotherm.     

Electroless deposition and characterization of Ni-P-WC composite alloys

A composite coating Ni-P-WC was produced using an electroless deposition technique from citrate bath containing WC powder. The influence of plating parameters such as WC content, pH, temperature and stirring rate on the content of WC codeposited with Ni-P alloys were investigated. The maximum value of WC (50-55 V_p) codeposited can be achieved at a particle content of 20 gL^− 1 in the electrolyte, at pH 5.5-6, temperature 85-90 °C and stirring rate of 150 rpm. Surface morphology and microstructure of Ni-P-WC coatings were determined by means of SEM and X-ray diffraction. It was found that the phase structure of the solid solution cannot be varied by codeposition of WC particles in Ni-P alloys, and it only influences the growth of the crystal planes. The properties of the composite such as hardness and abrasion resistance were also examined and compared with WC free nickel deposited layer. The presence of WC particles in the deposit significantly was found to improve the hardness and abrasion resistance of composite coatings.     

Effects of pre-treatments on the corrosion properties of electroless Ni-P layers deposited on AlMg2 alloy

Amorphous Ni-P layers with 8-10 wt.% phosphorus were deposited by sodium hypophosphite onto AlMg2 type aluminium alloy substrates after different pre-treatments. Prior to the electroless nickel-phosphorus (ENP) deposition in an acetate and lactic acid based nickel bath, the widely applied Zn (zincate) or Ni displacement (Ni strike) pre-treatments for aluminium substrates as well as a non-conventional surface conditioning one (soaking in a warm solution containing only hypophosphite and lactic acid) were all tested and their effects evaluated on the corrosion and other properties of the Ni-P layers developed right afterwards. The surface morphology and structure of the ENP layers were characterized by scanning electron microscopy and X-ray diffraction analysis. Polarization resistances were measured in 0.5 mol dm^− 3 Na₂SO₄ solution at pH 3. Compared to the direct electroless plating on the bare aluminium alloy AlMg2, it was found, that the hypophosphite adlayer (hypophosphite immersion pre-treatment) have also increased the corrosion resistance as the displacement pre-coatings, but without decreasing the deposition rate unlike conventional displacement methods. In the studied ENP deposition systems the decrease of corrosion rate could mainly be attributed to the lower microporosity and smoother morphology of the nickel-phosphorus coatings.     

NaCl溶液中腐蚀学因素对化学镀Ni－P合金腐蚀磨损行为的影响

在自行研制的腐蚀磨损试验机上，研究了腐蚀学因素对化学镀Ｎｉ－Ｐ合金腐蚀磨损行为的影响。结果表明，当ＮａＣｌ浓度为３．５％时，化学镀Ｎｉ－Ｐ合金的腐蚀磨损速率、摩擦系数和腐蚀磨损协同作用率具有峰值特性。ＮａＣｌ浓度升高将引起Ｎｉ－Ｐ合金的自腐蚀电位负移，温度升高将引起Ｎｉ－Ｐ合金的腐蚀磨损速率增大，协同作用率上升。化学镀Ｎｉ－Ｐ合金可以作为Ｇ１０５钢在ＮａＣｌ溶液中抵抗腐蚀磨损的表面改性材料。     

Nanoscratching deformation and fracture toughness of electroless Ni-P coatings

In the present investigation electroless Ni-P coatings were prepared. Structural characterizations indicated that the as-deposited coating had an amorphous structure with a P content of 23 at.%. The deformation behavior of an electrolessly amorphous Ni-P coating was investigated by using the Vickers indentation and the Tribo-indenter instrumented nano-indentation technique. The hardness of the Ni-P coating is remarkably improved after proper heat-treatment and the hardness is as high as 12.7 GPa for the coating annealed at 400 °C for 1 h. However, the cracks were observed during the indentation of the Ni-P coatings annealed at 400 °C and 500 °C for 1 h. The corresponding fracture toughness was evaluated as 2.58 MPa m^0.5 and 1.33 MPa m^0.5, respectively. Nanoscratching tests indicated that the wear resistance of the Ni-P coatings was improved significantly with an increasing ratio of hardness (H) to elastic modulus (E). It was observed that the friction coefficient increased from 0.083 ± 0.006 for the Ni-P coating annealed at 300 °C up to 1.337 ± 0.009 for the IF steel substrate, while the H/E simultaneously decreased from 0.084 (10.7/128) to 0.009 (1.85/200). The study revealed that the electrolessly amorphous Ni-P coating had offered better corrosion resistance than the Ni-P coatings after heat-treatment. An annealing temperature of 300 °C is preferentially suggested for the trade-off between the wear resistance property and anti-corrosion property of the Ni-P coating.     

ZL104合金表面化学镀镍磷合金层的研究

在ＺＬ１０４合金表面上进行Ｎｉ－Ｐ与Ｎｉ－Ｃｕ－Ｐ化学镀,以提高ＺＬ１０４合金材料的耐蚀性与耐磨性。结果表明：化学镀可以显著提高ＺＬ１０４合金表面的硬度,并改善其在５％ＮａＣｌ溶液中的耐蚀性;在２００～５２０℃温度下热处理后,镀层的硬度显著提高,但耐蚀性略有降低,这可能与镀层中的析出物Ｎｉ３Ｐ析出有关。     

中温酸性化学镀Ni-P合金耐蚀性能研究

为提高化学镀Ni-P合金耐蚀性能,以Q235钢为待镀基体,在中温的酸性条件下,采用正交试验方法得到镀层耐蚀性最佳的工艺条件为:镀液pH值 5.2;Ni2 与H2PO2-的摩尔比为0.48;复合络合剂乳酸15mL/L 丙酸5mL/L;加速剂NaF 0.4g/L;热处理温度500 ℃.在此条件下,腐蚀电流为2.166×10-5A,可较好地提高镀层耐蚀性.     

Annealing temperature effect on the corrosion parameters of autocatalytically produced Ni-P and Ni-P-Al2O3 coatings in artificial seawater

Ni-P and Ni-P-Al₂O₃ amorphous alloy coatings with 9.3 and 8.3 wt.% P respectively were obtained by autocatalytic deposition at 90 °C on carbon steel substrates. The effect of annealing temperature (100, 200, 300, 400 and 500 °C) upon the corrosion parameters of the coatings in artificial seawater with pH 5.0 and 8.1 at room temperature was evaluated by potentiodynamic polarisation and electrochemical impedance spectroscopy. It was found that deposits annealed at 400 and 500 °C presented an increase of the charge transfer resistance and negligible changes on samples annealed at lower temperature. Polarisation tests showed a charge transfer controlled anodic kinetics on both Ni-P and Ni-P-Al₂O₃ deposits and diffusion controlled cathodic reaction in artificial seawater at pH 5.0 and 8.1. The coatings did not present passive behaviour in the electrolytes and impedance measurements showed a single time constant for all cases with the lowest double layer capacitance (C_dl) for samples annealed at 400 and 500 °C. The best corrosion parameters were observed on Ni-P and Ni-P-Al₂O₃ coatings annealed at temperatures higher than 400 °C, which is the temperature where crystallisation of this kind of coatings takes place.     

化学沉积Ni—P合金层及Ni—P—SiC复合层的研究

本文通过对化学沉积Ni-P合金和Ni-P-SiC复合镀层的研究,找到了制取适宜的磷含量和SiC含量的工艺方法。介绍了所得沉积层具有较高硬度和优良的耐磨性,并列举了应用于工业生产的实例,预期这项技术具有较广阔的应用前景。     

Substituted uracils as corrosion inhibitors for copper in 3% NaCl solution

Substituted uracils were tested as corrosion inhibitors of copper in 3% NaCl medium using electrochemical polarisation, impedance measurements and non-electrochemical techniques (weight loss, IR and UV-visible). This study permitted to follow the evolution of the inhibitory effect of the uracil derivatives, according to their substituents, on copper in 3% NaCl medium. Comparison of results showed that dithiouracil (DTUr) was the best inhibitor. The maximum inhibition efficiency reached 98% at 10⁻³ M. DTUr adsorbs on the copper surface according to the Frumkin isotherm model.     

Improvements on the wear resistance of high thermal conductivity Cu alloys using an electroless Ni-P coating prior to PVD deposition

An attempt to improve the load support for hard PVD coatings on soft Cu alloys has been made by using a medium phosphorous content electroless Ni-P coating prior to PVD deposition, envisaging the application of these coating/substrate systems in plastic injection moulding. Several PVD coatings, including TiN, CrN, CrAlN, multilayered CrAlN, WC-C, multilayered CrAlN/WC-C were deposited onto an Ampcoloy 940 Cu alloy in two conditions: ‘standard’ and electroless Ni-P plated. The effect of the electroless Ni-P coating on the coating/substrate performance was evaluated by pin-on-disc wear and impact tests. Ultra-microhardness and surface roughness measurements were also used to characterise the resulting coating/substrate systems. The electroless Ni-P coating reduced the wear rates of the PVD-coated Cu alloys and increased the impact wear resistance. Among the PVD coatings trialled, CrN, CrAlN and multilayered CrAlN coatings on electroless Ni-P provided the lowest wear rates.     

Preparation of MgO coatings on magnesium alloys for corrosion protection

MgO coating is formed on magnesium alloy by anodic electrodeposition in 6 M KOH solution, whereas Mg(OH)₂ coating is produced by anodization in 10 M KOH solution, which could be successively converted to MgO by calcination in air at 450 °C. The evolution of morphology, structure and composition of anodic film obtained on Mg alloy is investigated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX) and X-ray diffraction (XRD). Potentiodynamic polarization measurements show that the as-grown MgO protective coatings are very effective in improving the corrosion resistance of magnesium alloy compared to bare metallic magnesium.     

镍磷非晶纳米晶复合镀层的制备及其耐蚀性

对电沉积12．3％P（质量分数）镍磷合金进行热处理，部分晶化获得非晶纳米晶复合镀层。利用X射线衍射仪、透射电镜和高分辨透射电镜分析镀层的结构。结果表明，镀态时镀层呈典型的非晶态结构，控制热处理工艺可得到非晶纳米晶的复合镀层。通过动电位极化曲线（3．5％NaCI溶液）测定，得知部分晶化的镀层耐蚀性得到改善。由于具有少量纳米晶相镶嵌于连续非晶相上，非晶纳米晶复合结构的镍磷合金镀层耐蚀性优于非晶态镍磷合金镀层。     

Corrosion behavior of electroless Ni-P alloy coatings containing tungsten or nano-scattered alumina composite in 3.5% NaCl solution

The corrosion protection performance of electroless deposited nickel-phosphorus (Ni-P) alloy coatings containing tungsten (Ni-P-W) or nano-scattered alumina (Ni-P-Al₂O₃) composite coatings on low carbon steel was studied. The effect of heat treatment on the coating performance was also studied. The optimum conditions under which such coatings can provide good corrosion protection to the substrate were determined after two weeks of immersion in 3.5% NaCl solution. Electrochemical impedance spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance before and after heat treatment. The Ni-P-W coatings showed the highest surface resistance compared with Ni-P-Al₂O₃ and Ni-P. The surface resistance of Ni-P-W coatings was 12.0 × 10⁴ Ω cm² which is about the double of the resistance showed by Ni-P-Al₂O₃ (7.00 × 10⁴ Ω cm²) and twenty times greater than the surface resistance of Ni-P (0.78 × 10⁴ Ω cm²). XRD analysis of non-heat-treated samples revealed formation of a protective tungsten phosphide phase. Heat treatment has an adverse effect on the corrosion protection performance of tungsten and alumina composite coatings. The surface resistance decreased sharply after heat treatment.     

AZ31镁合金轧态薄板化学镀Ni-P合金的工艺研究

为了改善AZ31镁合金轧态薄板的耐腐蚀性能,通过正交试验优化了化学镀Ni-P的配方及工艺,并对Ni-P镀层的形貌、镀层厚度、镀层中P元素的含量以及镀层在3．5％NaCI溶液中的极化曲线进行了测试和表征。结果表明,AZ31镁合金化学镀Ni—P的最优方案为：碱式碳酸镍10g／L,次亚磷酸钠25g/L,温度80％,pH值=8。所得的Ni—P镀层均匀,无明显缺陷,厚度约为18～23μm,P元素的质量分数为9．68％。试样经化学镀Ni—P后的自腐蚀电位大幅度提高,出现了约600mV的钝化区间,其耐蚀性能明显提高。     

碳钢Ni-P化学镀耐碱性溶液腐蚀性能的研究

为了研究碳钢材料在碱性介质中的腐蚀以及防护方法,采用静态浸泡法以及电化学的方法,对普碳钢以及进行化学镀后的耐碱液腐蚀性能进行了研究.结果表明:普碳钢在室温碱性溶液中放置1h后,表面即发生了严重的腐蚀.在碱性溶液中浸泡24h后,出现了基体局部剥离的现象.普碳钢在碱性溶液中发生了严重的腐蚀.在施加了化学镀层后,普碳钢在碱性溶液中浸泡24h后,表面光洁完整,与未施加化学镀层相比,有很小的腐蚀电流.在碳钢表面施加化学镀层后在碱性介质中具有良好的耐腐蚀性.