The Structure and Protective Properties of Zinc and Nickel Alternate Electrodeposits

A NEW TYPE of coatings consisting of a large numberof laminar deposits has been the keen subject of muchresearch,because these layered-structure coatingspossess improved properties or novel phenomenon suchas increased mechanical strength,micro-hardness,giantmagnetoresistance and corrosion resistance[1"6'.Thesecoating systems with individual layers making upoverall structure are also called compositionallymodulated multilayer(CMM)coatings'3"5'.In view ofthe plating historical use of surface…     

The physical and electrochemical properties of electroless deposited nickel–phosphorus black coatings

The manufacture of electroless black nickel surfaces had been obtained, through etching electroless nickel deposits by oxidizing acid solution. The morphology, chemical composition and reflectance of pre-etch and post-etch coatings were compared to examine influence of phosphorus and sulfur content on preparation of black surfaces. The non-metallic elements content of electroless nickel deposits was greatly improved after black treatment. It indicated the etching treatment was a selective dissolving process. The nickel atoms can be preferentially removed during the period. Optimum phosphorus content range to produce low reflectance black surface was proposed, after reflectance measurement of black surfaces. Additionally, the effect of co-deposited phosphorus and sulfur atoms on corrosion resistance of electroless nickel deposits was evaluated by electrochemical impedance spectroscopy (EIS). The fitting results indicated that corrosion resistance of high-phosphorus electroless nickel deposits will be significantly reduced after black treatment. However, that of low-phosphorus deposits will be improved.     

Einfluß von Beschichtungen auf das Schwingungsrißkorrosionsverhalten des Chromstahls X20Cr13

Influence of coatings on the corrosion fatigue behaviour of 13% chromium steel The influence of coatings on the corrosion fatigue behaviour of 13% chromium steel has been studied. There have been selected different coating systems: Barrier coating (enamel), diffusion coatings, (aluminizing, chromizing) and anodic coating, (aluminium, zinc, tin, cadmium). The corrosion fatigue limits of coated with uncoated specimens in neutral NaCl-solution are compared. Salt-concentrations were 0,01 and 22% (? 0,38 M) NaCl at 80°C and 150°C. The tests were carried out with alternating tensions and a constant frequency of 50 Hz. Only the use of andic coatings improved the corrosion fatigue behaviour of the chromium steel.     

Corrosion Resistance of Nickel+Chromium Deposits: Influence of Insoluble Non-Metallic Additives in Nickel Solutions

Recent research has shown that substantial improvements in the corrosion resistance of nickel+chromium coatings on steel and zinc-base alloy die castings can be obtained by the use of multiple deposits of these metals, plated under differing conditions. Certain decorative nickel deposits produced by codepositing various very fine, bath-insoluble non-metallic particles in the plate obtained from semi-bright and bright nickel electroplating solutions have also been found to lead to improved corrosion resistance, when they are used as the top plate in multiple-layer systems before the final chromium is applied. Accelerated and outdoor exposure tests are described and the theoretical basis of the results obtained is discussed.     

Elektrochemische Untersuchungen zur Korrosion von Nickelüberzügen

Electrochemical investigations into the corrosion of nickel coatings The corrosion behaviour of pure rolled sheet nickel, electrodeposited nickel and electroless Ni-P-alloy-coatings is investigated by electrochemical methods. Some mechanisms of corrosion and passivation in 0,1 N H₂SO₄ and deionated water - both with addition of several anions - are described.     

Vergleich des SwRK-Verhaltens eines auf hohe Duktilität vergüteten martensitaushärtenden PH 13-8 Mo Stahls mit dem Dampfturbinenlaufschaufelstahl X20 CrMoV 12 1

Corrosion fatigue behaviour of the to high ductility aged precipitation hardened steel PH 13-8 Mo and the X20 CrMoV 121 steam turbine blading steel in comparison The corrosion fatigue behaviour of the martensitic stainless steels PH 13-8 Mo and X20 CrMoV 121 is compared. The investigation includes both electrochemical and corrosion fatigue tests. Also mechanical, metallographical and SEM investigations were performed. The corrosion fatigue resistance at 150°C of the precipitation hardened steel PH 13-8 Mo in the modification with the higher strength level (cast I) varies between 100 and 135 MPa. The mean stress was 250 MPa. The influence of the pH-value is predominant to the Cl^? -concentration. The corrosion fatigue resistance of the lower strength modification of PH 13-8 Mo (cast II) is significant lower than that of cast 1. At the conventional 12% Cr-steel cracks are initiated from notches caused by corrosion under salt like deposits primarily at the grain boundaries, weakened by carbide precipitations. At the PH 13-8 Mo steel the crack initiation is located at zones of plastic deformation between the martensitic laths. Corrosion attack occurred preferably by orthogonal orientation of the laths to the surface.     

Korrosionsverhalten von Hybridschichtsystemen

Corrosion behaviour of hybrid coating systems Potentiodynamic methods were used to investigate the corrosion protection value of various hybrid coating systems. Combinations of galvanic chromium and electroless nickel interlayers with titanium nitride and chromium nitride coatings produced by sputterion-plating method were tested. Anodic polarization curves show that corrosion resistance is strongly connected with the microdefects present in the coatings. The coating system consisting of chromium nitride with electroless nickel as an interlayer exhibits excellent corrosion resistance properties in 1N H₂SO₄ solution. The reason for this behaviour is presented and discussed in detail.     

Protective coating on Mg AZ91D alloy - The effect of electroless nickel (EN) bath stabilizers on corrosion behaviour of Ni-P deposit

The effects of the electroless nickel (EN) bath stabilizers; thiourea (TU) and maleic acid (MA), on the corrosion of the EN coatings on Cu and Mg substrates were investigated in an aggressive oxygenated chloride environment.Corrosion was limited to the external EN layer, and thus, the intermediate Cu layer as well as Mg AZ91D substrate remained intact. On the EN surface, two different types of corrosion morphologies were observed. Specimens prepared with TU showed preferential attack along particle boundaries, while pitting corrosion was observed for specimens prepared either without a stabilizer or with MA. The latter deposits showed higher corrosion resistances due, in part, to the formation of a P-enriched layer on the surface. The poorer corrosion performance of EN specimens prepared with TU was attributed to the presence of the particle boundaries and the trace impurities adsorbed on, or included in, them. The key impurity was sulphur incorporated during formation of deposits in TU-stabilized baths.It was clearly shown that the corrosion behaviour of the EN specimens was predominantly influenced by the morphological and surface compositional aspects of the deposits.     

Corrosion properties of double layer nickel coatings obtained by pulse plating techniques

Abstract

In this study, the influence of pulse plating on the microstructure, morphology and corrosion properties of semibright nickel layers was investigated and it was observed that applied pulse sequences led to deposits with higher corrosion resistance than those obtained by direct current. Moreover, the study of the effect of pulse plated semibright nickel deposits on double layer nickel coatings showed that the applied pulse sequences provoked an increase in potential difference between individual nickel layers, favouring the lateral spread of pitting corrosion and reducing its penetration to substrate. In addition, the influence of the applied pulse sequences on the consumption of the organic additives in the semibright nickel electrolyte was evaluated, observing that this influence was similar to that given by direct current.     

Multifunctional epoxy coatings combining a mixture of traps and inhibitor loaded nanocontainers for corrosion protection of AA2024-T3

This work aims at investigating the corrosion protection effectiveness of multifunctional epoxy coatings modified with pigments such as ceramic nanocontainers loaded with corrosion inhibitor, chloride and water traps, applied on AA2024-T3. Characterizations on the morphology, composition and structure of the coatings were conducted. The corrosion resistance was studied by electrochemical impedance spectroscopy, localized electrochemical impedance spectroscopy and scanning vibrating electrode technique. The mechanical behaviour of the coatings was examined through nanoindentation and nanoscratching tests. Electrochemical and nanomechanical testing results, evidenced the improvement of the corrosion protective properties and mechanical behaviour of the coatings in the presence of the various pigments.     

Microstructure and Properties of Nickel Layers Electrodeposited under Reduced Pressure and Temperature Gradient Conditions

前期研究表明,在5 k Pa恒负压和35℃/65℃温度梯度和无添加剂的条件下,能以高达1 mm/h的沉积速度制备出表面光滑、近无沉积缺陷且多项性能优越的镍镀层。本实验则重点研究负压、温度梯度等条件参数对镍沉积层形貌、织构和性能的影响。研究结果显示:负压和温度梯度大小对沉积层的形貌、织构与硬度、耐腐蚀等性能都有一定程度的影响;只有在贴近阴极面的液层处于沸腾状态时才能获得良好的镍沉积层;增大温度梯度和(或)降低沉积槽气压都有利于细化晶粒、提高硬度和耐酸腐蚀性;温度梯度对镍沉积层的织构特征影响作用明显,但负压大小对镍层的择优取向几乎没有影响。镍沉积层上述形貌、织构与性能的变化主要归结于负压电沉积的沸腾驱动传质效应与真空脱气效应。     

Mechanical and corrosion properties of dc magnetron sputtered Al/Cr multilayers

Mechanical and corrosion properties of Al/Cr multilayer coatings deposited by dc magnetron sputtering are investigated and compared to pure Al and Cr coatings. The objective of this study is to increase the mechanical properties of sacrificial Al-based coatings. The results indicate that mechanical and corrosion properties depend on the architecture organisation. The reduction of the layer thickness allows an increase of the coating hardness. The nanolayer architecture leads to a “hard and tough” material compared to the other architectures. Moreover, the intrinsic corrosion resistance is enhanced, as the corrosion and the pitting corrosion potentials are progressively shifted towards positive values. The nanolayer coating presents the highest intrinsic corrosion resistance but multilayer and nanolayer Al/Cr coatings become nobler than the steel substrate. The corrosion resistance of the coated steel is then strongly dependent on the microscopic coating defects which act as preferential pathways for the corrosive solution. So the nanolayer architecture organisation improves the mechanical properties but does not permit to conserve the sacrificial behaviour of the aluminium based coating, which is harmful for the corrosion protection of coated steel.     

Water-Lubricated Ni-Based Composite(Ni-Al_2O_3,Ni-SiC and Ni-ZrO_2)Thin Film Coatings for Industrial Applications

In this work,pure nickel and Ni-based nanocomposite coatings(N1-Al_2O_3,Ni-SiC and Ni-ZrO_2) were produced on steel substrate by using pulse electrodeposition technique.The industrial performance tests were conducted to evaluate the wear resistance,corrosion resistance,adhesion strength and wettability behaviour of newly developed coatings.Rolling contact ball-on-disc tribometer was used to assess anti-wear behaviour of these coatings under waterlubricated contacts.The results showed that the wear- and corrosion resistance properties of nickel alumina and Ni-SiC composite coatings significantly improved than that of pure Ni and Ni-ZrO_2 coatings.The adhesion and wettability results of Ni-Al_2O_3 composite showed better performance when compared to the rest of the coatings.The effects of incorporating nanoparticles on the surface microstructure,interface adhesion and distribution of the particles were also investigated.The coatings were characterized by using scanning electron microscopy,X-ray diffraction analysis and 3D white light interferometry.The wear failure behaviour of these coatings was further examined by post-test surface observation under optical microscope.     

Corrosion Behavior of Reverse-Pulse Electrodeposited Zn-Ni Alloys in Saline Environment

The study investigates the relationship of the reverse-pulse electrodeposited zinc-nickel alloy coatings’ characteristics and their corrosion behaviors in a saline environment, using both anodic polarization and electrochemical impedance analysis. The introduction of anodic pulsation gives deposits of more refined grain sizes and increased nickel contents, resulting in improvement of the corrosion resistance. High anodic current densities employed in the reverse-pulse electrodeposition, however, modulate crystallographic orientations of the grains, introduce porosity to the structure, and hence adversely affect the corrosion resistance of the coating deposits.     

Wear and corrosion resistance of laser remelted and plasma sprayed Ni and Cr coatings on copper

Nickel and chromium coatings were produced on the copper sheet using plasma spraying and laser remelting. The sliding wear test was achieved on a block-on-ring tester and the corrosion test was carried out in an acidic atmosphere. The corrosive behaviors of both coatings and original copper samples were investigated by using an impedance comparison method. The experimental results show that the nickel and chromium coatings display better wear resistance and corrosion resistance relative to the original pure copper sample. The wear resistance of the coatings is 8 - 12 times as large as original samples, and the wear resistance of laser remelted samples is better than that of plasma sprayed ones. The corrosion resistance of laser remelted nickel and chromium samples is better than that of plasma sprayed samples respectively. The corrosion rate of chromium coatings is less than that of nickel coatings, and the laser remelted Cr coating exhibits the least corrosion rate.     

Electrochemical behaviour of high phosphorus electroless Ni–P–Si3N4 composite coatings

Abstract

A high phosphorus electroless nickel bath was used to prepare plain Ni–P and composite coatings containing submicrometre size silicon nitride particles. Deposits were characterised for their composition, morphology and electrochemical behaviour. Codeposition of particles in a Ni–P matrix has not influenced the phosphorus content (10 wt-%). Surface morphology of plain Ni–P deposits was smooth; the composite deposits became slightly rough with small nodules due to particle incorporation. Cross-sectional examination of composite coating revealed that the particles were uniformly distributed throughout the thickness of the coating. Potentiodynamic polarisation and electrochemical impedance studies were carried out in 3·5 wt-% sodium chloride solution in non-deaerated condition. Potentiodynamic polarisation studies showed that the corrosion current density value obtained for composite coatings is lower than that for plain Ni–P coatings. Electrochemical impedance spectroscopy studies showed that the coating resistance of the composite coating is higher than that of plain Ni–P coating. This was further confirmed by SEM analysis of corroded samples.     

Prevention of nickel release from electroplated articles in the context of allergic contact dermatitis: further outcomes

‘Nickel Allergy’ sometimes occurs when nickel-containing articles are in direct and prolonged contact with the skin, leading to corrosion of elemental nickel by sweat, liberating sufficient nickel ions to be absorbed through the skin and initiate an allergenic effect. EU ‘Nickel Restrictions’ impose limits on the amount of nickel released from articles intended for use in this application but permits a non-nickel surface coating that can ensure the rate of nickel release does not exceed 0.5?μg?cm^?2?week^?1 after 2 years of normal use. The official tests for coated items are simulated wear and corrosion under EN 12472 followed by determination of nickel release under EN 1811, and articles shall not be placed on the market unless they pass these tests. A paper published in Transactions during 2015 reported bright nickel coatings with top coats that would prevent nickel release and pass these tests. Regular chromium deposited from a hexavalent electrolyte was the benchmark, with microporous chromium and supplementary organic coatings evaluated for improved performance. All prevented nickel release, but the best low-cost commercial coating was regular (conventional) chromium deposited from a hexavalent electrolyte. Further tests reported here were conducted to evaluate bright nickel deposits with top coats of tin–cobalt alloy, and of hexavalent chromium with supplementary coatings of coloured physical vapour deposition and electrophoretic coatings. Tests with trivalent chromium top coats deposited from proprietary chloride and sulphate electrolytes showed that regular (conventional) chromium over bright nickel failed the nickel release test. But microporous trivalent chromium deposits passed the tests satisfactorily.     

Microstructure and Performances of Nanocrystalline Zinc-nickel Alloy Coatings

THE STUDY on zinc-nickel alloy coatings isdeveloped rapidly because of their higher corrosionresistance and better mechanical characteristics[1-8].The zinc-nickel coatings provide improved corrosionprotection for steels in relatively aggressiveenvironments.It has been found that the maximumprotective ability can be reached with the nickel contentbetween12%and15%[9].Recently,several newzinc-nickel alloy technologies have been developed[10-15]and further researches for better coating andchara…     

Investigation of high-performance acid zinc nickel electrolyte

Zinc nickel alloy coatings are increasingly demanded by the automotive industry due to their highly improved corrosion protection over pure zinc and other zinc alloy coatings. To produce zinc nickel coatings with a nickel incorporation of 12 to 16%, mainly alkaline zinc nickel electrolytes are used in the plating industry. Continuous improvements in the field of acidic zinc nickel alloy electrolytes now meet the needs of the automotive industry while being advantageous in specific fields of application.In this paper, zinc nickel coatings deposited from alkaline as well as from ammonium-free acid zinc nickel electrolytes are investigated. The morphology is evaluated by scanning electron microscopy; the texture is investigated by focused ion beam, and X-ray diffraction patterns identify the structure of the coating. The corrosion protection of the zinc nickel coatings and the adhesion of the zinc nickel coatings have been bench-marked. For applications on fasteners, the coefficients of friction have been measured and compared.     

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.