Corrosion resistance of multilayer coatings of nanolayered Cr/Ni electrodeposited from Cr(III)-Ni(II) bath

In this study the corrosion resistance of chromium and nickel single layers and multilayer coatings of nanolayered Cr/Ni, electrodeposited from Cr(III)-Ni(II) baths on low carbon steel substrates, has been studied. The coatings were electrodeposited from a bath using pulse current and modulated agitation. The total thickness of single layer and multilayer coatings was fixed at 5 μm and multilayer coatings with different modulation wavelengths and Cr to Ni thickness ratio were electrodeposited. Corrosion behavior of coatings was then studied by using potentiodynamic polarization test and electrochemical impedance spectroscopy in 0.1 M H₂SO₄. The results showed that Cr and Ni single layers had low corrosion resistance due to the presence of surface cracks and pores, respectively. On the other hand, optimized 20 nm Cr/50 nm Ni multilayer deposition significantly improved corrosion resistance.     

Microstructure and wear resistance of electrodeposited RE-Ni-Mo-P-B4C-PTFE composite coating

Abstract

The structure, hardness and wear resistance of RE-Ni-Mo-P-B₄C-PTFE composite coating have been studied by means of X-ray diffraction, scanning electron microscopy, abrasion testing and microhardness testing. The results show that the structure of RE-Ni-Mo-P-B₄C-PTFE composite coating experiences a transformation from amorphous via a mixture to crystalline as the heat treatment temperature is increased. Crystalline particles in the coating become gradually finer with the addition of B₄C, B₄C plus polytetrafluoroethylene (PTFE) and B₄C plus PTFE plus rare earths (RE), in that order. The hardness and wear resistance of the RE-Ni-Mo-P-B₄C-PTFE composite increase with increasing temperature, reaching peak values at 400°C and 300°C, respectively. The wear resistance of the composite coating is greatly superior to that of other traditional coatings.     

Balancing the corrosion resistance and through-plane electrical conductivity of Cr coating via oxygen plasma treatment

Developing an electrically conductive and corrosion-resistant coating is essential for metal bipolar plates of polymer electrolyte membrane fuel cells(PEMFCs). Although enhanced corrosion resistance was seen for Cr coated stainless steel(Cr/SS) bipolar plates, they experience a quick decrease of through-plane electrical conductivity due to the formation of a porous and low-conductive corrosion product layer at the plate surface, thus leading to an increase in interfacial contact resistance(ICR). To tackle this issue, the multilayer Cr coatings were deposited using the magnetron sputtering with a remote inductively coupled oxygen plasma(O-ICP) in the present study. After the O-ICP treatment, a Cr oxide layer(Cr O*) is formed on the specimen surface. The Cr O*/Cr/SS has a remarkably lower stable corrosion rate(iss) than that of the native Cr oxides(Cr On/Cr/SS). Compared with Cr On/Cr/SS, the excellent performance of Cr O*/Cr/SS is attributed to a denser and thicker surface layer of Cr O* with Cr being oxidized to its highest valence state,Cr(VI). More importantly, the through-plane electrical conductivity of the specimens treated by the optimized O-ICP decreases much slowly than Cr On/Cr/SS and thus, the increament of ICR of Cr O*/Cr/SS after the potentiostatic polarization test is considerably smaller than that of Cr On/Cr/SS, which is benefited from the reduced issthat mitigates the deposition of corrosion products and hinders further oxidation of Cr coating. Therefore, Cr O*/Cr/SS proves to be a well balanced trade-off between corrosion resistance and through-plane electrical conductivity. The results of this study demonstrate that O-ICP treatment on a conductive metal coating is an effective strategy to improve the corrosion resistance and suppress the increase of ICR over the long-term polarization. The technique reported herein exhibits its promising potential application in preparing corrosion resistant and electrically conductive coatings on metal bipolar plates to be used in PEMFCs.     

Effects of nano-diamond particles on the structure and tribological property of Ni-matrix nanocomposite coatings

Microcrystalline Ni (m-Ni) and nanocrystalline Ni (n-Ni) based composite coatings were prepared by a conventional electrodeposition method from a Watts-type electrolyte containing nano-diamond particles. Effects of nano-diamond particles on the microstructure, surface morphology, microhardness and wear resistance of two different Ni-matrix composites were investigated comparatively. Our present study shows that in the case of m-Ni matrix, the incorporation of nano-diamond particles significantly affects the microstructure, mechanical and tribological properties of corresponding composites. As to the n-Ni matrix, however, above properties were only slightly affected by the presence of nano-diamond particles, and the n-Ni matrix composites exhibit much poorer anti-wear performance than pure n-Ni under dry sliding wear conditions.     

镀锌板表面有机硅烷-磷化复合膜与阴极电泳漆膜配套性研究

本文介绍了一种可以满足阴极电泳涂装要求的有机硅烷化的磷化处理液,对有机硅烷化的磷化转化膜进行电化学、耐碱性、溶出率、硫酸铜点滴测试,结果显示当有机硅烷和磷化成分配比为8：2时,其耐蚀性最好。通过分析入槽前干膜和湿膜的电化学等性能,发现无论是湿膜或干膜在一定条件下均能得到均一致密的膜层。讨论不同电泳电压、电泳时间对膜厚以及膜外观的影响,当电泳电压为150V、电泳时间为120s时,可形成性能优异的电泳漆膜。     

Characteristics and performance of hard Ni60 alloy coating produced with supersonic laser deposition technique

A novel coating fabrication technique, known as supersonic laser deposition (SLD), which combines cold spray (CS) with laser technology, is applied to produce hard Ni60 (58–62 HRC) coating on medium carbon steel (AISI 1045 steel) substrate. Different process parameters are investigated to obtain the optimal. The Ni60 coating specimens prepared by SLD process are studied microstructurally using scanning electron microscope (SEM), energy dispersive spectrum (EDS) and X-ray diffraction (XRD). The microstructures of the coatings are compared with those of the coatings produced using laser cladding (LC). The hardness, tribological property and corrosion resistance of the Ni60 coatings produced by SLD and LC with the optimal process parameters are evaluated under Vickers hardness, pin-on-disk wear and electrochemical corrosion tests. It is demonstrated that the Ni60 coating with SLD exhibits some characteristics, such as fine microstructure as cast, stable phases and less dilution; it surpasses the coating produced with conventional LC process in sliding wear resistance; but in 1 mol/L H₂SO₄ solution, the SLD and LC coatings performed similarly in corrosion resistance. This research has proved that SLD technique enables depositing hard Ni60 on steel substrate, which is impossible for CS technique.     

Characterization and properties of CuZrAlTiNi high entropy alloy coating obtained by mechanical alloying and vacuum hot pressing sintering

CuZrAlTiNi High entropy alloy (HEA) coating was synthesized on T10 substrate using mechanical alloying (MA) and vacuum hot pressing sintering (VHPS) technique. The MA results show that the final product of as-milled powders is amorphous phase. The obtained coating sintered at 950 °C is compact and about 0.9 mm in thickness. It is composed of a couple of face-centered cubic (FCC), one body-centered cubic (BCC) solid solutions and AlNi₂Zr phase. The interface strength between coating and substrate is 355.5 MPa measured by three point bending test. Compared with T10 substrate, the corrosion resistance of CuZrAlTiNi HEA coating is enhanced greatly in the seawater solution, which is indicated by the higher corrosion potential, wider passivation region, and secondary passivation. The average microhardness of the coating reaches 943 HV_0.2, and is about 3.5 times higher than the substrate, which is mainly ascribed to the uniformly dispersed nano-size precipitates, phase boundary strengthening and solid solution strengthening. Moreover, the wear resistance of the coating is slightly improved in comparison with the substrate.     

Characterization of Cr(VI) binding and reduction to Cr(III) by the agricultural byproducts of Avena monida (oat) biomass

Chromium contamination of the environment has become an important issue due to the potential health threat it poses. Conventional technologies to clean up heavy metal ions from contaminated waters have been utilized, but these technologies are not cost-effective. However, the use of agricultural waste byproducts for the removal of Cr(VI) from contaminated waters may be a new cost-effective alternative. Oat byproducts from the Juarez Valley in Mexico were studied for the ability to bind Cr(VI) under different temperature and time conditions. The metal binding ability of oat byproducts was calculated from experimental data collected at temperatures of 8, 26, and 54°C, and time exposures of 1, 6, 24, 48, and 72 h at each temperature. These results showed that the binding of Cr(VI) to oat biomass increased as time and temperature increased. The bound chromium was recovered from the oat biomass by treatment with 0.2 M HCl. Through the use of X-ray absorption spectroscopy, the reduction of Cr(VI) to Cr(III) was determined to occur by the oat byproducts. These results indicate that the use of agricultural waste byproducts could be a better alternative for the removal and subsequent reduction of Cr(VI) to Cr(III) from contaminated waters.     

Effect of Cr interlayer on the adhesion and corrosion enhancement of nanocomposite TiN-based coatings deposited on stainless steel 410

Applications of hard protective nanocomposite coatings are frequently limited by insufficient adhesion related to high stress. In the present work, we study the effect of an intermediate Cr layer on top of the stainless steel 410 (SS410) substrate on the performance of the nanocomposite (nc) TiN-based coatings prepared by plasma enhanced chemical vapor deposition. The Cr layer was found to enhance the corrosion resistance of the SS410 substrate by a factor of 280 in terms of corrosion current, and to increase adhesion of the TiN coating by a factor of 4. We show that for the nc-TiN/a-SiN_x and nc-TiCN/a-SiCN coatings, the substantial improvement of the corrosion resistance can be attributed to the combination of the inertness of the Cr layer, and of the densely packed homogeneous nc structure of the nc coatings containing Si and/or C in comparison to columnar crystalline TiN coatings.     

Influence of CO2 laser heat treatment on surface properties,electrochemical and tribological performance of HVOF sprayed WC–24%Cr3C2–6%Ni coating

In this investigation, the tribological and electrochemical performances of HVOF sprayed WC–24%Cr₃C₂–6%Ni coatings before and after laser heat (LH) treatment were investigated. In the wear test, the friction and wear resistance of the coatings were improved significantly with an optimized LH process. The improvement can be attributed to the improved roughness and hardness, as well as the formation of oxide tribofilms. With LH treatment, the local corrosion of the coating had a decrease and the pit corrosion resistance of the WC–24%Cr₃C₂–6%Ni coating was improved as a result of the decreasing the size and number of the porosities, especially compact interface achieved by LH treatment.     

Effect of encapsulation with zeolite and coating with TiO2 on the thermal stability of caffeine during melt extrusion of a PET/TiO2@(zeolite/caffeine) nanocomposite

The practice of encapsulating a functional material in a thermally stable porous material displays great potential in preventing decomposition during high-temperature processing. In this study, caffeine encapsulated in zeolite was coated with TiO₂ to withstand high-temperature melt extrusion with poly(ethylene terephthalate) (PET). Two coating processes were trialed: in situ encapsulation and coating where TiO₂ precursor was added to zeolite/caffeine solution; and ex situ coating in which pre prepared zeolite/caffeine capsules were added to the TiO₂ precursor for coating. The TiO₂-coated nanocomposites were melt-extruded with PET at 285?°C. Residual amounts of caffeine confirmed the shielding effect of the TiO₂ coating during the high-temperature melt extrusion. The in situ TiO₂ coating process was more effective than the ex situ process.     

浸涂法荷电微孔滤膜基本结构及性能研究

论述了浸涂法荷正电微孔滤膜的基本结构及性能．电镜照片及孔径分布曲线显示,浸涂工艺不会改变膜的微孔结构,膜的孔径分布也非常均匀,但孔径尺寸减小,变化率小于10％．与基膜相比,荷电膜的外形尺寸、透水率及孔隙率减小,泡点压力及拉伸强度增加,而且具有明显的正电性能及吸附分离性能．     

聚苯胺的制备及其在压载舱涂料中的防腐性能

为满足《船舶专用海水压载舱和散货船双弦侧处所保护涂层性能标准》对压载舱涂层的防腐性能要求,开发新型聚苯胺(PANI)涂层.通过化学氧化法制备聚苯胺,并采用扫描电镜和透射电镜对其进行了形貌观察.将质量分数为5%和10%的聚苯胺添加到呋喃氧茚树脂中制备船舶压载舱防腐涂料,涂覆于Q235碳钢表面.通过附着力测试、极化曲线测试、电化学阻抗谱等表征手段,评价其力学及防腐性能,并初步探讨其防腐机理.结果表明:制备的聚苯胺有纳米纤维网状结构,有利于增加树脂的交联程度,可起到屏蔽作用;添加聚苯胺后,SEM中基体与涂层之间的界面不明显,且涂层缺陷及孔隙变少;5%PANI和10%PANI涂层的附着力分别达12.3和11.8 MPa,涂层的附着力显著提高,符合PSPC的要求;聚苯胺涂层的自腐蚀电流密度下降,自腐蚀电位正移,阻抗弧半径变大,防腐性能有了较大的提高;质量分数5%的聚苯胺涂层试样较10%试样的力学及防腐性能均有所提高,能为Q235碳钢提供更好的保护.     

Effect of operating parameters and chemical treatment on the tribological performance of natural fiber composites: A review

The demand for high-performance engineering products made from natural resources is increasing because of the low-cost, low-density, biodegradability, renewable nature and lighter than synthetic fibers. With these characteristics, the tribological performance of natural fiber composite has become an important element to be considered in most industrial and manufacturing functions. This paper presents an overview of the factors that influence the tribological performance of natural fiber composites, which include applied load, sliding distance, sliding velocity and fiber orientation. Influences of chemical treatment is also reviewed and illustrated through scanning electron microscope (SEM) observations. This review will focus on kenaf fibers (KFs) and oil palm fibers (OPFs) which have been widely exploited over the past few years among the available natural resources. The results show that the operating parameter, fiber orientation and chemical treatment has significant effects on the tribological performance of natural composite. A clear understanding of the factors that affect the tribological performance is very essential in performance improvement on natural fibers reinforced polymer composite for potential applications.     

Effect of Pr2O3 on the microstructure and hydrogen evolution property of nickel sulphur coatings electrodeposited on the nickel foam substrate

This paper studies the effect of the Pr₂O₃ addition on the hydrogen evolution property and microstructures of the Ni-S coating electrodes. The coating electrodes with and without Pr₂O₃ have been prepared through electrodeposition using a modified Watts bath. Results indicated that Ni-S coating with Pr₂O₃ shows a much better electrocatalytic activity than that without Pr₂O₃. XRD and SEM results indicated that the high electrocatalytic activity for the Ni-S coating with Pr₂O₃ addition is due to the larger surface area and amorphous microstructure.     

Materials selection for hot stamped automotive body parts: An application of the Ashby approach based on the strain hardening exponent and stacking fault energy of materials

Complex stamping operations are becoming widespread in the automotive industry to produce vehicle body parts with adequate mechanical strength and reduced wall thickness. The need for weight reduction drives the development of new metallic materials capable of achieving a good balance between formability and mechanical properties. Advanced high strength steels play a major role in this scenario. The aim of this work was to develop a materials selection strategy for hot stamped automotive body parts using the Ashby approach. The selection process was based on the formability of metallic alloys derived from two fundamentals materials properties, the strain hardening exponent and the stacking fault energy.     

用倍率与循环测试探讨LiFePO_4/C核壳材料的碳层构筑条件

磷酸铁锂材料的碳层构筑问题在文献中众说纷纭,难以把握具体细节。然而,倍率性能和循环性能是锂电材料的重要电化学性能,因此通过倍率性能和循环性能的测试,来理清单质型碳源和化合物型碳源的作用区别,同时对碳含量、碳化条件的影响开展研究。探讨了单质型(纳米石墨粉、乙炔黑)和化合物型(羟乙基纤维素、聚乙二醇2000、葡萄糖)碳源对LiFePO4/C电化学性能的影响。实验结果表明,葡萄糖和纳米石墨粉的综合性能优于其它碳源;使用同一种碳源时,碳含量和煅烧温度对材料高倍率性能的影响显著大于对低倍率性能的影响;碳含量和煅烧温度一定时,碳源种类对LiFePO4/C的低倍率初始性能有所影响,对其低倍率循环性能有较为显著的影响,对其高倍率性能则有非常显著的影响。     

High-velocity oxygen-fuel spray parameter optimization of nanostructured WC–10Co–4Cr coatings and sliding wear behavior of the optimized coating

In this paper, the Taguchi method was employed to optimize the spray parameters (spray distance, oxygen flow and kerosene flow) to achieve the highest hardness and, in turn, the best wear resistance of the high-velocity oxygen-fuel (HVOF) sprayed nanostructured WC–10Co–4Cr coating by investigating the correlation between the spray parameters and the hardness. The important sequence of spray parameters on the hardness of the coatings is kerosene flow > oxygen flow > spray distance, and the kerosene flow is the only significant factor. The optimal spray parameter (OSP) for the coating is obtained by optimizing hardness (330 mm for the spray distance, 2000 scfh for the oxygen flow and 6.0 gph for the kerosene flow). The coating deposited under the OSP with low porosity and high microhardness consists predominately of WC and a certain amount of W₂C phases. The coating deposited under the OSP exhibits better wear resistance compared with the cold work die steel Cr12MoV. The material removal of the coating is the extrusion of the ductile Co–Cr matrix followed by the crack and the removal of the hard WC particles.     

Identification of the optimal product configuration and parameters based on individual customer requirements on performance and costs in one-of-a-kind production

One-of-a-kind production (OKP) aims at manufacturing products based on the requirements from individual customers while maintaining the high quality and efficiency of mass production. This research addresses the issues in identifying the optimal product configuration and its parameters based on individual customer requirements on performance and costs of products. In this work, variations of product configurations and parameters in an OKP product family are modeled by an AND-OR tree and parameters of the nodes in this tree. Different product configurations with different parameters are evaluated by performance and cost measures. These evaluation measures are converted into comparable customer satisfaction indices using the non-linear relations between the evaluation measures and the customer satisfaction indices. The optimal product configuration and its parameters with the maximum overall customer satisfaction index are identified by genetic programming and constrained optimization. A case study to identify the optimal configuration and its parameters of window products in an industrial company is used to demonstrate the effectiveness of the introduced approach.