Preparation and tribological behavior of electrodeposited Ni-W-GO composite coatings

Ni-W-GO composite coatings were successfully plated on 45# steel substrate by co-electrodeposition technique in a Ni-W electrolyte solution,with different contents of graphene oxide(GO)nanoparticles in suspension.The structure,phase composition and surface morphology of as-plated composite coatings were characterized by Raman,X-ray diffraction(XRD),scanning electron microscopy(SEM)attached with energy disperse spectroscopy(EDS),respectively.The hardness and tribological behavior of the present coatings were also evaluated by Vickers Hardness tester and high-speed reciprocating friction and wear tester,and the wear mechanism was discussed as well.The results show that layer-structured GO nanoparticles significantly affect the microstructure and grain size of the Ni-W-GO composite coatings.Meanwhile,GO nanoparticles embedded in NiW-GO coatings can obviously improve the hardness and wear resistance in comparison with the corresponding NiW coatings.The highest microhardness and wear resistance of Ni-W-GO composite coatings are obtained with 0.15 g·L~(-1)GO employing.     

Morphology and corrosion resistance of composite coatings obtained by phosphating and molybdate post-sealing on galvanized steel

The phosphated hot-dip galvanized （HDG） sheets were post-sealed with sodium molybdate solution to improve the corrosion resistance of phosphate coatings. The morphology, chemical composition and corrosion resistance of the coatings were investigated using scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, Tafel polarization measurements and neutral salt spray （NSS） tests, and were compared with those of the single coatings. The results show that post-sealing the phosphated HDG steel with molyhdate solution, the pores among the zinc phosphate crystals are sealed with molybdate films containing Zn, P, O and Mo, and the continuous composite coatings are formed. The suppression of both the anodic and the cathodic processes of zinc corrosion on the samples are enhanced significantly. The synergistic corrosion protection effect of the single phosphate coatings and molybdate films for zinc is evident. The corrosion resistance of the composite coatings increases with phosphating time up to 300 s.     

Wear and Friction Properties of Electrodeposited Ni-Based Coatings Subject to Nano-enhanced Lubricant and Composite Coating

This paper presents research findings on the tribological performance of electrodeposited coatings subject to nano-lubricants with the addition of nano-Al_2O_3 and graphene and Ni/nano-Al_2O_3 composite coatings. Electrodeposited coatings were produced by using a pulse electrodeposition method. Tribological experiments were conducted by using a linear reciprocating ball on flat sliding tribometer. Experimental results confirmed that the wear and friction resistance properties were significantly enhanced by doping of nano-effects in the lubricating oil and composite coating. The addition of Al_2O_3 nanoparticles in the lubricating oil showed the best tribological properties, followed by Ni–Al_2O_3 composite coatings and nano-oil with graphene. The surface morphology and microstructure of electrodeposited coatings were examined by scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction. The wear mechanisms of these coatings subjected to tribological testing were investigated by post-test surface analyses. This research provides a novel approach to design durable nano-coatings for tribological applications in various industries such as automotive,aerospace, locomotive and renewable energy technologies.     

Preparation of Ni-CNT composite coatings on aluminum substrate and its friction and wear behavior

Nickel-carbon nanotube(CNT) composite coatings with a Zn-Ni interlayer were prepared by electrodeposition technique on aluminum substrate. The effects of CNT concentration in plating bath on the volume fraction of CNTs in the deposits and the coating growth rate were investigated. The friction and wear behavior of the Ni-CNT composite coatings were examined using a pitt-on-disk wear tester under dry sliding eonditions at a sliding speed of 0.062 3 m/s and load range from 12 N to 150 N. Because of the reinforcement of CNTs in the composite coatings, at lower applied loads, the wear resistance was improved with increasing volume fraction of CNTs. Since cracking and peeling occur on the worn surface, the wear rates of composite coatings with high volume fraction of CNTs increase rapidly at higher applied loads. The friction coefficient of the composite coatings decreases with the increasing volume fraction of CNTs due to the reinforcement and self-lubrication of CNTs.     

Aluminum-silicon carbide coatings by plasma spraying

An aluminum base composite (Al-SiC) powder has been developed for producing plasma sprayed coatings on Al and other metallic substrates. The composite powders were prepared by mechanical alloying of 6061 Al alloy with SiC particles. The concentration of SiC was varied between 20 and 75 vol%, and the size of the reinforcement was varied from 8 to 37 μm in the Al-50 vol% SiC composites. The 44 to 140 μm composite powders were sprayed using an axial feed plasma torch. Adhesion strength of the coatings to their substrates were found to decrease with increasing SiC content and with decreasing SiC particle sizes. The increase in the SiC content and decrease in particle size improved the erosive wear resistance of the coatings. The abrasive wear resistance was found to improve with the increase in SiC particle size and with the SiC content in the composite coatings.     

Effect of silicate pretreatment, post-sealing and additives on corrosion resistance of phosphated galvanized steel

Sodium silicate （water glass） pretreatment before phosphating, silicate post-sealing after phosphating and adding silicate to a traditional phosphating solution were respectively carried out to obtain the improved phosphate coatings with high corrosion resistance and coverage on hot-dip galvanized（HDG） steel. The corrosion resistance, morphology and chemical composition of the coatings were investigated using neutral salt spray（NSS） tests, scanning electron microscopy（SEM） and energy dispersive spectroscopy（EDS）. The results show that pretreatment HDG steel with silicate solutions, phosphate coatings with finer crystals and higher coverage are formed and the corrosion resistance is enhanced. Adding silicate to a traditional phosphating solution, the surface morphology of the coatings is nearly unchanged. The corrosion resistance of the coatings is mainly dependent on phosphating time. Phosphating for a longer time （such as 5 min）, the corrosion resistance, increasing with concentration of silicate, is improved significantly. Post-sealing the phosphated HDG steel with silicate solutions, the pores among the zinc phosphate crystals are sealed with the films containing Si, P, O and Zn and the continuous composite coatings are formed. The corrosion resistance of the composite coatings, related to the pH value, contents of hydrated gel of silica and Si2O^2- 5 and post-sealing time, is increased markedly. The improved coatings with optimal corrosion resistance are obtained for phosphating 5 min and post-sealing with 5 g/L silicate solution for 10 min.     

Preparation of calcium phosphate coatings on Mg-1.0Ca alloy

The calcium phosphate coatings were prepared by virtue of electrochemical deposition in order to improve the corrosion resistance of Mg-1.0Ca alloys in simulated body fluids.The chemical compositions,structures and morphologies of the coatings were investigated by energy dispersive spectroscopy(EDS),X-ray diffractometry(XRD)and scanning electron microscopy(SEM), respectively.The potentiodynamic electrochemical technique was employed to investigate the bio-degradation behavior of Mg-1.0Ca alloys with Ca-P coatings in Hank's solutions.The experimental results show that the deposited coatings predominately consist of flake-shape brushite(DCPD,CaHPO4·2H2O)crystallites.The corrosion resistance of the substrates with coatings is improved in Hank's solutions significantly.     

Bioactivity of bioresorbable composite based on bioactive glass and poly-L-lactide

Bioactive and bioresorbable composite was fabricated by a solvent evaporation technique using poly-L-lactide（PLLA） and bioactive glass （average particle size： 6.8μm）. Bioactive glass granules are homogeneously distributed in the composite with microcrack structure. The formation of hydroxyapatite（HA） on the composite in simulated body fluid（SBF） was analyzed by scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS）, X-ray diffraction（XRD）, and Raman spectra. Rod-like HA crystals deposit on the surface of PLLA/bioactive glass composite after soaking for 3 d. Both rod-like crystals and HA layer form on the surface for 14 d in SBF. The high bioactivity of PLLA/bioactive glass composite indicates the potential of materials for integration with bone.     

PREPARATION OF TEM THIN FOIL CONTAINING POWDER PARTICLE BY ELECTRODEPOSITION METHOD

A practical technique to prepare transmission electron microscopy （TEM） thin foil containing powder particle was described and the data for the codeposition of two type particles with copper in the electroplating were presented. By depositing the particles which were distributed in CuSO4 electrolyte on cathode together with Cu^2＋ in electrodeposition bath, composite coating with suitable thickness could be formed. The thin coating was separated from the substrate and cut into a disc with diameter of 3mm for electropolishing. When the Cu matrix was thinned during electropolishing, the particles contained in the coating plate were also thinned to meet the suitable thickness for TEM observation. Various experimental results revealed that during electrodepositing the current density, pH-value of electrolyte and stirring mode all have significant effects on the distribution of particles in composite coating and the surface quality of the composite coating. The proper parameters used during electrodepositing to prepare TEM thin foil containing powder particle were discussed.     

Influence of Zn and Mg Alloying on the Corrosion Resistance Properties of Al Coating Applied by Arc Thermal Spray Process in Simulated Weather Solution

In this study,Al–Zn and Al–Mg coatings were deposited on steel substrates by an arc thermal spray process.X-ray diffraction and scanning electron microscopy were used to characterize the deposited coatings and corrosion products.Open circuit potential(OCP),electrochemical impedance spectroscopy,and potentiodynamic studies were used to assess the corrosion characteristics of these coatings after exposure according to the Society of Automotive Engineers(SAE)J2334 solution of varying durations.This solution simulates an industrial environment and contains chloride and carbonate ions that induce corrosion of the deposited coatings.However,the Al–Mg alloy coating maintained an OCP of approximately-0.911 V versus Ag/Ag Cl in the SAE J2334 solution even after 792 h of exposure.This indicates that it protects the steel sacrificially,whereas the Al–Zn coating provides only barrier-type protection through the deposition of corrosion products.The Al–Mg coating acts as a self-healing coating and provides protection by forming Mg_6Al_2(OH)_(16)CO_3(Al–Mg layered double hydroxides).Mg_6Al_2(OH)_(16)CO_3has interlocking characteristics with a morphology of plate-like nanostructures and an ion-exchange ability that can improve the corrosion resistance properties of the coating.The presence of Zn in the corrosion products of the Al–Zn coating allows dissolution,but,at the same time,Zn_5(OH)_6(CO_3)_2and Zn_6Al_2(OH)_(16)CO_3are formed and act to reduce the corrosion rate.     

Microstructure, morphology and electrochemical property of RuO270SnO230 mol% and RuO230SnO270 mol% coatings

The DSA anodes based on RuO₂–SnO₂ oxides are most employed in chlorine-alkali cells. Their properties are strongly influenced by the mixed-oxide coating structures. In this paper, two RuO₂–SnO₂/Ti DSA anodes with different Ru and Sn molar ratios were prepared through a sol–gel technique. The nano-structure, morphology, grain structure and composition of the coatings were investigated by means of XRD, SEM and TEM. XRD analysis indicates two rutile-type solid solutions are formed. Peak profile analysis shows that in the solid solution where SnO₂ is the major component smaller crystallites (about 20–30 nm) are formed than in those where RuO₂ is the major component (about 100–200 nm). The SEM images reveal the coating with high level of SnO₂ possesses more accumulated and compact structures. The EDS analysis indicates that two DSA anodes coatings in which SnO₂ is similar to the designed concentration are prepared by the sol–gel method. TEM characterization shows the polygonal crystallites are present in the obtained RuO₂–SnO₂ coatings. The voltages of Cl₂-evolution and O₂-evolution suggest both RuO₂–SnO₂/Ti DSA anodes have a good electrochemical performance and can be used for the chlorite industrial productions.     

钛合金表面激光熔覆高温自润滑耐磨复合涂层

为了提高钛合金的摩擦学性能,采用激光熔覆技术在Ti-6Al-4V合金表面制备了γ-NiCrAlTi/TiC与γ-NiCrAlTi/TiC/CaF₂复合涂层. 采用 X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)分析了涂层的物相和显微组织,在球-盘式高温摩擦磨损试验机上测试了不同温度下(室温,300 ℃,600 ℃)复合涂层的摩擦学性能. 结果表明,激光熔覆的复合涂层与基体呈冶金结合,γ-NiCrAlTi/TiC/CaF₂复合涂层主要由"原位"生成的小块状,针状TiC颗粒及TiC树枝晶,γ-NiCrAlTi固溶体基体及弥散分布的球状CaF₂颗粒组成. 由于硬质增强相 TiC与增韧相γ-NiCrAlTi的共同作用,γ-NiCrAlTi/TiC与γ-NiCrAlTi/TiC/CaF₂复合涂层的磨损率在试验温度下都远低于Ti-6Al-4V基体;在600 ℃时,γ-NiCrAlTi/TiC/CaF₂涂层的平均摩擦系数为0.21,相对于基体与γ-NiCrAlTi/TiC涂层分别降低了43%,50%,表现出良好的高温自润滑减摩性能.     

Wear behaviour of thermal flame sprayed FeCr coatings on plain carbon steel substrate

The principle aim of this study is to investigate the wear behaviour of FeCr coatings on Ni-based bond deposited plain carbon steel substrate for several applications in power generation plants. For this purpose, FeCr and Ni-based powders were sprayed on plain carbon steel substrates using a thermal flame spray technique. Fabricated layers were characterized by using a X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), microhardness and surface roughness testers. FeCr coatings were subjected to sliding wear against AISI 303 stainless steel counter bodies under dry and acidic environments. A pin-on-plate type of apparatus was used with normal loads of 49 and 101 N and sliding speed of 1 Hz. XRD results revealed that FeCr, Fe, Cr, Fe–Cr–Ni, γ-Fe₂O₃ and Fe₃O₄ phases are exist in the coating. In addition, some inhomogenities such as oxides, porosity, cracks, unmelted particles and inclusions were observed by SEM. The surface morphologies of FeCr samples after wear experiments were examined by SEM and EDS. It was found that friction coefficients of the coatings in dry condition are higher than that in acidic environment.     

Preparation and characterization of electroless Ni-P-Fe3O4 composite coatings and evaluation of its high temperature oxidation behaviour

Ni-P coatings modified with synthetic magnetite were prepared by electroless technique from a Ni-P plating bath containing magnetite powder. The coatings morphology was studied by means of scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The corrosion resistance at room temperature of the Ni-P films modified with magnetite was evaluated by means of electrochemical impedance spectroscopy (EIS), where the composite films exhibited a better behaviour. The films resistance to high temperature oxidation was evaluated by cyclic oxidation tests, SEM/EDS and X-ray diffraction analysis (XRD), where the coating with iron oxides appears to be more protective.     

Phase transformation and morphology of the intermetallic compounds formed at the Sn–9Zn–3.5Ag/Cu interface in aging

The morphology and phase transformation of the intermetallic compounds (IMCs) formed at the Sn–9Zn–3.5Ag/Cu interface in a solid-state reaction have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The monoclinic η′-Cu₆Sn₅ transforms to the hexagonal η-Cu₆Sn₅ and the orthorhombic Cu₅Zn₈ transforms to the body-centered cubic (bcc) γ-Cu₅Zn₈ as aged at 180 °C. The scallop-shaped Cu₆Sn₅ layer is retained after aging at 180 °C for 1000 h. In the solid-state reaction, Ag is repelled from η′-Cu₆Sn₅ and reacts with Sn to form Ag₃Sn, and the Cu₅Zn₈ layer decomposes. Kirkendall voids are not observed at the Sn–9Zn–3.5Ag/Cu interface even after aging at 180 °C for 1000 h.     

SnO2 coated Ni particles prepared by fluidized bed chemical vapor deposition

A Fluidized Bed Metal–Organic Chemical Vapor Deposition (FB-MOCVD) process was developed for the growth of tin oxide thin films on large hollow Ni particles. Tetraethyl tin was used as tin source and dry air both as fluidization gas and oxidant reagent. The SnO₂ films were grown in a FBCVD reactor under reduced pressure (13.3 kPa) in the temperature range of 633–663 K. A series of specific experiments was carried out to optimize the design of the reactor and to determine the range of experimental parameters (flow rate, pressure, temperature) leading to good fluidization of the large hollow Ni particles used as base material. The SnO₂ films deposited on particles exhibited a dense nodular surface morphology similar to that previously observed on flat substrates. The relative thickness of the films was determined by EDS analyses and the real values were measured by SEM on cross-sections of particles. The SnO₂ films exhibit satisfactory thickness uniformity from one particle to another in the same batch and from run to run. XRD studies revealed that the films exhibited good crystallinity with the cassiterite structure. Traces of NiO were found at the SnO₂/Ni interface. Finally, the SnO₂ CVD coated-Ni particles were used as anodes in an electrochemical cell. The potential limit of oxygen evolution measured was that of the SnO₂ layer despite the initial porosity of the hollow Ni particles inherent to their preparation. This work is the first step towards the preparation of high specific surface area electrodes.     

双层WC颗粒增强铁基体复合熔覆层的组织和性能研究

采用氩弧熔覆(GTAW)技术在45号钢表面制备了双层WC颗粒增强铁基体复合涂层,通过SEM,XRD和EDS分析了熔覆层的显微组织和相组成,并测试了熔覆层的显微硬度.结果表明:双层复合熔覆层内未见明显裂纹、夹杂等缺陷,与基体呈冶金结合;熔覆层的显微组织由未熔WC颗粒、灰色等轴状初晶和鱼骨状共晶碳化物组成;复合熔覆层的显微...     

热处理对化学沉积Ni-Zn-P-TiO2复合镀层的影响

采用化学沉积方法获得Ni-Zn-P-TiO2复合镀层.采用X射线衍射、扫描电子显微镜、能谱分析等手段对复合镀层进行表征,研究了不同热处理状态下复合镀层的显微硬度、耐蚀性及耐冲蚀特性.结果表明,复合镀层由锐钛矿的纳米TiO2颗粒和过饱和的镍固溶体所构成.对经过不同热处理温度后复合镀层的分析表明,300℃以下热处理时,复合镀层衍射图无明显变化;加热至400℃时,有Ni3P析出;加热至500℃时,有Ni5Zn12析出.经400℃×1 h热处理,复合镀层具有最大的硬度值.复合镀层经300℃×1 h热处理后质量损失最低,有最好的耐蚀性能.在介质流速为36 ml/s、冲击角度为45.条件下,经过300℃× 1 h热处理后的复合镀层质量损失最低.     

Microstructure and tribological properties of laser clad Ti2Ni3Si/NiTi intermetallic coatings

Wear resistant Ti₂Ni₃Si/NiTi full intermetallic composite coatings with a microstructure consisting of ternary metal silicide Ti₂Ni₃Si primary dendrites and interdendritic Ti₂Ni₃Si/NiTi eutectic were fabricated on a substrate of 0.2%C low carbon steel by the laser cladding process using Ti-Ni-Si alloy powders as the precursor materials. Microstructure of the coatings was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDS). Wear resistance of the laser clad Ti₂Ni₃Si/NiTi intermetallic coatings was evaluated under dry sliding wear test conditions at room temperature. Results indicate that the Ti₂Ni₃Si/NiTi intermetallic coatings have excellent abrasive and adhesive wear resistance under dry sliding wear test conditions because of the unique combination of high yield strength and toughness of the intermetallic compound NiTi and the high hardness, strong covalent dominant atomic bonds and possible strong hardness anomaly of the ternary metal silicide Ti₂Ni₃Si with MgZn₂ type Laves crystal structure.     

均一亚微米级氧化铈抛光粉的制备

为得到均一的亚微米级二氧化铈（CeO₂）抛光粉,以六水合硝酸铈（Ce(NO₃)₃·6H₂O）为原料,以醇－水混合溶液为溶剂,采用溶剂热法合成CeO₂。改变Ce3+浓度和醇-水体积比,利用X射线衍射仪（XRD）、激光粒度分布仪、扫描电子显微镜（SEM）对CeO₂的物相组成和形貌特征进行表征,分析CeO₂粒子的形成过程。将合成的CeO₂用于6H-SiC晶片Si面的化学机械抛光（chemical mechanical polishing,CMP）,利用原子力显微镜（atomic force microscopy, AFM）和电子天平得出CeO₂的抛光性能。结果表明:Ce3+浓度为0.10 mol/L,醇－水体积比为3∶1时合成的CeO₂的形貌规则、晶粒尺寸适中且粒度分布均匀。采用其抛光后,晶片表面粗糙度R_a为0.243 nm,材料去除速率d_MRR为287 nm/h。合成的CeO₂适用于化学机械抛光。