Effect of SiC/nano‐CeO2 on wear resistance and microstructures of Ti3Al/γ‐Ni matrix laser‐cladded composite coating on Ti–6Al–4V alloy

The Ti–6Al–4V alloy is an important aviation material, but has a poor resistance to slide wear. Laser cladding of the Al₃Ti + Ni/Cr/C + TiB₂/Al₂O₃ + SiC/nano‐CeO₂ preplaced powders on the Ti–6Al–4V alloy can form the Ti₃Al/γ‐Ni matrix composite coating, which improves the wear resistance of the substrate. In this study, the Al₃Ti + Ni/Cr/C + TiB₂/Al₂O₃ + SiC/nano‐CeO₂ laser‐cladded coating was researched by means of X‐ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. The experimental results indicate that under the action of SiC/nano‐CeO₂, this composite coating exhibited a fine microstructure. Furthermore, the proper content of nano‐CeO₂ decreased the crack tendency. The results above indicated that, it is feasible to improve the tribological property of the Al₃Ti + Ni/Cr/C + TiB₂/Al₂O₃ laser‐cladded coating by adding of SiC/nano‐CeO₂. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and properties of Ni–Co–P/nano‐sized Si3N4 electroless composite coatings

Ni–Co–P/nano‐sized Si₃N₄ composite coating was successfully fabricated on aluminum alloys by electroless plating in this work. The surface and cross‐sectional morphologies, composition, microstructure, microhardness, friction and wear behavior of deposits were investigated with SEM, EDS, XRD, Vickers hardness and high‐speed reciprocating friction, respectively. It was found that a Ni–Co–P/nano‐sized Si₃N₄ composite coating on aluminum alloy substrate is uniform and compact. The existence of nano‐sized Si₃N₄ particles in the Ni–Co–P alloy matrix causes a rougher surface with a granular appearance, and increases the microhardness but decreases the friction coefficients and wear rate of electroless coatings. Meanwhile, the effects of heat treatment at 200, 300, 400 and 500 °C for 1 h on the hardness and tribological properties were researched. It is revealed that both of the microhardness and tribological properties of Ni–Co–P coatings and Ni–Co–P/Si₃N₄ composite coatings increase with the increase of heating temperature in the range of 200–400 °C, but show different behavior for the two coatings after annealing at 500 °C. Copyright © 2011 John Wiley & Sons, Ltd.     

Corrosion behavior of electroless Ni–P/TiO2 nanocomposite coatings

Composite Ni–P/nano‐TiO₂ coatings were prepared by simultaneous electroless deposition of Ni–P and nano‐TiO₂ on a low carbon steel substrate. The deposition was carried out from stirred solutions containing suspended nano‐TiO₂ particles. The Ni–P and Ni–P/nano‐TiO₂ coatings before and after heat treatment were characterized by X‐ray diffraction, scanning electron microscopy and energy dispersive X‐ray spectroscopy. The micro‐structural morphologies of the coatings significantly varied with the nano‐TiO₂ content. The corrosion resistance of as‐plated and heat‐treated Ni–P and Ni–P/nano‐TiO₂ coatings was investigated by anodic polarization, Tafel plots and electrochemical impedance spectroscopic (EIS) studies in 3.5% NaCl solution. Ni–P/nano‐TiO₂ coating exhibited superior corrosion resistance over Ni–P coating. Copyright © 2015 John Wiley & Sons, Ltd.     

Impact of Al nanoparticles upon the microstructure and wear properties of Ni-Cr-Al nanocomposite coatings

Ni–7Cr and Ni–7Cr–2Al (wt.%) nanocomposite coatings were fabricated by co-electrodeposition of Ni with Cr (40 nm) or and Al (75 nm) nanoparticles from a nickel sulfate bath, their microstructure, friction and wear performance were comparably evaluated in order to elucidate the effect of Al nanoparticles on the properties of nanocomposite coatings. The results indicated that the co-deposition of minor Al nanoparticles significantly increases the microhardness and wear resistance because Al nanoparticles with surface amorphous oxides layers exert the dispersion-strengthening effect like Al₂O₃ nanoparticles.     

Optimization of electroless Ni?P coatings based on multiple roughness characteristics

This paper presents an experimental study of roughness characteristics of electroless Ni? P coatings. Optimization of coating process parameters is done with multiple surface roughness characteristics based on Taguchi method coupled with grey relational analysis. Experiments are carried out by utilizing the combination of process parameters based on L₂₇ Taguchi orthogonal design with three process parameters, viz. bath temperature, concentration of nickel source solution and concentration of reducing agent. Results show that concentration of the reducing agent and its interaction with concentration of the nickel source solution have significant influence in controlling the roughness characteristics of electroless Ni? P coating. Grey‐based Taguchi method is found to optimize the coating parameters fairly well. The surface morphology and composition of coatings are also studied with the help of scanning electron microscopy, energy dispersed X‐ray analysis and X‐ray diffraction analysis. No significant change in nickel and phosphorous content of coatings occurs with annealing. The Ni? P deposit is nanocrystalline in the as‐plated condition, and upon heat treatment at 400 °C it produces Ni₅P₂, Ni₂P, and NiP₂ as major compound constituents. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of Y2O3 on microstructural characteristics and wear resistance of cobalt‐based composite coatings produced on TA15 titanium alloy surface by laser cladding

The effects of Y₂O₃ on the microstructure, phase composition of the coatings, microhardness and wear resistance of cobalt‐based composite coatings prepared by laser cladding were investigated. The TA15 titanium alloy was selected as substrate which the cobalt‐based composite powder with different content of Y₂O₃ was cladded on. The microstructure of the coatings was observed by scanning electron microscope (SEM) and metallurgical microscope. The phase structure of the coatings was determined by X‐ray diffraction (XRD), and the microhardness and wear resistance of the coatings were measured by hardness tester and wear testing machine. The results show that the rare earth oxide Y₂O₃ can refine and purify the microstructure of the coatings, reduce the porosities and cracks and improve compactness of the coatings. Moreover the addition of Y₂O₃ improves the microhardness of the coatings and reduces the friction coefficient, thus improving the wear property of the coatings. And the wear resistance of the coating with Y₂O₃ has improved about 50 times; the highest value of microhardness in the coating is HV1181.1. And 0.8 wt% content of Y₂O₃ in the coating is the best choice for improving the microhardness and wear resistance of the coating. It is feasible to improve the microstructure and tribological properties of laser cladding coatings by adding of Y₂O₃. Copyright © 2014 John Wiley & Sons, Ltd.     

Microstructural characteristics of Ce conversion coatings on Cf/Al composite or Ni?P plated Cf/Al composite

The microstructural characteristics of Ce conversion coatings on carbon fiber reinforced Al matrix (Cf/Al) composites and Ce conversion coatings on Ni? P plated Cf/Al composites were studied by SEM, AFM, TEM and XPS. The Ce conversion coating on the Ni? P plated composite does not have obvious microcracks, which can be found easily in Ce conversion coatings. The Ce conversion coating on Ni? P plated composite has a lower surface roughness profile arithmetic mean deviation (R_a) than Ce conversion coating, as seen by AFM. Because of the inhomogeneity of the material surface and the different levels of deposition of Ce conversion coatings at the different sites, nonhomogeneous sites would promote microcrack formation of the Ce conversion coatings. The Cf/Al composite surface has lessuniformity than Ni? P plated composite, leading to more prominent microcracks. Selected area electron diffraction (SAED) patterns of Ce conversion coating could not be indexed nor matched closely to any of the oxides (Ce₂O₃, Ce₇O₁₂, Ce₆O₁₁) or hydroxides (Ce(OH)₃) that are listed in the Powder Diffraction File maintained by Diffraction Data, but for Ce conversion coating on the Ni? P plated composite the data matched closely with that of CeO₂ or Ce₆O₁₁. The XPS results showed that the Ce conversion coating mainly contained both Ce³⁺ and Ce⁴⁺ species, but Ce⁴⁺ species were the dominant oxidation state on Ni? P coating with Ce conversion deposition. Copyright © 2008 John Wiley & Sons, Ltd.     

Inclusion of W in electroless Ni–B coating developed from a stabilizer free bath and investigation of its tribological behaviour

In the present study, tribological and corrosion behaviour of electroless Ni–B–W (ENB-W) coatings prepared from stabilizer-free baths and deposited on AISI 1040 steel substrates were examined. Three distinct coating bath temperatures (85 °C, 90 °C, and 95 °C) were varied for coating deposition. The coatings showed nodular morphology. Thermogravimetric study of ENB-W coatings revealed improved thermal stability attained at 95 °C bath temperature. The microhardness of ENB-W coating was 645, 690, and 720 HV₁₀₀ at bath temperatures of 85 °C, 90 °C, and 95 °C respectively. The inclusion of W to Ni–B coating enhanced the hardness by ∼150 HV₁₀₀. On a pin-on-disc tribometer, wear test was conducted. The precipitation of Ni (111) and its borides occurred post sliding wear at high temperatures (300 °C). Ni (111) crystallite size decreased because of high temperature sliding wear at 300 °C with an increase in coating bath temperature. With a reduction in crystallite size at high temperatures, both wear rate and COF decreases. The scratch hardness and first critical load of failure of the coatings was determined using a scratch tester. Using potentiodynamic polarization, corrosion resistance of ENB-W coatings in 3.5% NaCl was investigated. ENB-W coatings could provide shielding to AISI 1040 steel from corrosion. Though the corrosion resistance is poor with respect to lead stabilized coatings.     

LaNi1 − x Cu x O3 (x = 0.05, 0.10, 0.30) coated electrodes for oxygen evolution in alkaline medium

LaNi_1???x Cu _x O₃ (x?=?0.05, 0.10, 0.30) coated electrodes were prepared by brush painting using Ni foam substrates in order to increase its active surface area. For comparison, coatings with x?=?0.05 were also prepared using vitreous carbon substrates. Cyclic voltammetry was used to evaluate the coating roughness (R _f). Values between 5,145?±?148 and 6,334?±?277 were obtained, depending on the x value, for the coatings on Ni foam. These results show that the electrodes prepared with LaNi_1???x Cu _x O₃ powder, obtained at 600 °C, lead to a big increase on the oxide electrode roughness when compared with LaNiO₃ electrodes prepared by a similar method. Much lower values were obtained for the coatings on vitreous carbon indicating that the substrate nature is also a key factor for the preparation of high surface area electrodes. The calculated kinetic parameters for the oxygen evolution reaction (OER) show that the partial replacement of Ni by Cu has no beneficial effect on the intrinsic catalytic activity of the coatings. On the other hand, a big increase on the active area is observed even for small amounts of Cu (x?=?0.05), leading to a better overall OER performance for the LaNi_0.95Cu_0.05O₃ coating on Ni foam. For this composition, the activity is dominated by geometric effects.     

Effect of Sintering Temperature on the Corrosion and Wear Behavior of Protective SiO2-Based Sol-Gel Coatings

Sol-gel hybrid organic-inorganic and inorganic SiO₂-based protective coatings with and without added 3 m glass particles were developed and tested for their corrosion and wear behavior of an stainless steel substrate (AISI316L). The corrosion resistance greatly increases by incorporating glass particles in the sols. The incorporation of particles in the coatings allows the synthesis of thicker crack-free coatings. On the other hand, the corrosion resistance increases for coatings with a higher organic content obtained at lower sintering temperature. These coatings are also highly stable in saline aqueous solutions. However, the wear resistance is badly affected by the hybrid character of the SiO₂ matrix. The optimum coating process in terms of corrosion and wear resistance, appears to be a hybrid system with a dense SiO₂ network achieved at intermediate sintering temperatures.     

Surface modifications of Li-ion battery electrodes with various ultrathin amphoteric oxide coatings for enhanced cycleability

Ultrathin ZnO, ZrO₂, and Al₂O₃ surface coatings are deposited via atomic layer deposition (ALD) with high conformality and atomic scale thickness control to enhance the electrochemical performance of LiMn₂O₄ for applications in lithium ion batteries. Two types of ALD-modified LiMn₂O₄ electrodes are fabricated: one is ALD-coated LiMn₂O₄ composite electrode and the other is electrode composed of ALD-coated LiMn₂O₄ particles and uncoated carbon/polyvinylidenefluoride network. Cycling performance and cyclic voltammetric patterns reveal that ZnO ALD coating is the most effective protective film for improving the electrochemical performance of LiMn₂O₄ at either 25 or 55 °C, followed by ZrO₂ and Al₂O₃. After 100 electrochemical cycles in 1 C at 55 °C, the electrode consisting of LiMn₂O₄ particles coated with six ZnO ALD layers (as thin as ~1 nm) delivers the highest final capacity, more than twice that of the bare electrode. It is also found that amphoteric oxide coating on LiMn₂O₄ particles can enhance the cycleability of LiMn₂O₄ more effectively than coating on the composite electrode. Furthermore, for ALD coating either on the composite electrode or on LiMn₂O₄ particles, the effect of oxide ALD modification for improving capacity retention and increasing specific capacity of LiMn₂O₄ is more phenomenal at elevated temperature than at room temperature.     

不同载体Ni基负载型催化剂对甲烷部分氧化制合成气催化行为研究

采用浸渍法制备了单一载体(Al₂O₃、ZrO₂、CeO₂)和ZrO₂、CeO₂改性的Al₂O₃复合载体的Ni催化剂,考察了在甲烷部分氧化制备合成气反应中的催化性能。通过N₂-物理吸附、H₂程序升温还原、X射线衍射、NH₃程序升温脱附和程序升温氧化等技术对催化剂进行了表征。结果表明,在单一载体催化剂中,Ni/Al₂O₃具有较大的比表面积,其初始反应活性较高,但该催化剂表面易形成大量的积炭而快速失活。Ni/ZrO₂和Ni/CeO₂催化剂比表面积较小,活性金属Ni在其表面分散性差,催化剂具有较低的CH₄转化率。而CeO₂和ZrO₂改性的Al₂O₃复合载体催化剂,具有较大的比表面积,反应活性明显高于单一载体催化剂。CeO₂-Al₂O₃复合载体催化剂具有最高的反应活性和较好的反应稳定性。同时表明,含CeO₂催化剂反应后表面积炭较少,CeO₂的储放氧功能增强了催化剂对O₂的活化,提高催化剂活性的同时,可以抑制积炭的生成。     

Formation of Superhydrophobic Alumina Coating Films with High Transparency on Polymer Substrates by the Sol-Gel Method

Transparent, superhydrophobic coating films have been prepared on polymer substrates at low temperatures through the sol-gel method. Al₂O₃ gel films were prepared on poly(ethylene terephthalate) substrates from Al(O-sec-C₄H₉)₃ chemically modified with ethyl acetoacetate. A small roughness of about 20–50 nm was found to form on the surface of the Al₂O₃ gel films dried at room temperature and then immersed in hot water at 60°C. The electron diffraction measurements have shown that this roughened surface consists of pseudoboehmite nanocrystals. The coating of hydrolyzed fluoroalkyltrimethoxysilane on the Al₂O₃ gel films with the small roughness produced transparent, superhydrophobic films with contact angle for water larger than 150°.     

Conversion‐coating treatment applied to in situ TiB2p reinforced Al?Si‐alloy composite for corrosion protection

In this work, continuous conversion coatings on the surface of in situ TiB₂ particulate reinforced A356 composite were formed successfully by cerium surface treatment for the first time. Scanning electron microscope (SEM) analysis showed that the conversion coatings were inhomogeneous and could be divided into two types of regions, namely, fine crack region and noncrack region. Many cerium‐rich nano‐nodules were uniformly distributed in the whole coatings. Energy dispersive spectroscopy (EDS) analysis testified that the crack coatings mainly covered the interdendritic sites occupied by TiB₂ particulates and Si phases. X‐ray photoelectron spectroscopy (XPS) analysis indicated that the conversion coatings were composed of CeO₂, Ce₂O₃, Ce(OH)₄, Ce(OH)₃, and a little amount of Al₂O₃. The electrochemical polarization tests showed that the cerium‐conversion treatment markedly improved the corrosion resistance of in situ TiB_2p/A356 composite in chloride environment, and the protection degree of the coatings was superior to that of conventional chromate‐conversion coating. According to these results, the formation mechanism of cerium‐conversion coatings was discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Ultrasound technique as a tool for high-rate incorporation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in NiCo layers

NiCo–Al₂O₃ composite coatings were prepared by electrodeposition in a sulfamate plating bath containing Al₂O₃ particles to be co-deposited under sonication. For reliable determination of the microstructure, detailed studies on composite cross-sections were carried out by energy-dispersive spectrometer (matrix composition, particle content) and FE-SEM/electron backscattered diffraction data (particle distribution, grain size), accompanied by XRD analyses concerning texture, lattice parameter, grain size, and residual stress. The NiCo matrix with a Co/Co + Ni ratio up to 0.4 is a face-centered cubic solid solution with <100> and <110> fiber textures. The distribution of the particles (size 250 nm) was well-dispersed and enhanced up to 15 wt.% by ultrasound application during plating. Vickers hardness increased up to 50% by dispersion hardening. First-order residual stress in the matrix increased with rising Co content, thus decreasing wear resistance and revealing the complex of composite properties with partially opposite effects.     

Fabrication,morphology and mechanical properties of Al2O3–Al graded coatings on China low activation martensitic steel substrates

Al₂O₃, Al₂O₃/Al and Al₂O₃–Al graded coatings were fabricated on China low activation martensitic steel and silicon substrates by RF magnetron sputtering. The coating composition and cross‐section morphologies were investigated using X‐ray photoelectron spectroscopy, Auger electron spectroscopy and field‐emission scanning electron microscopy. The mechanical properties of the coatings were studied using nanoindentation, wafer‐curvature measurements and microscratch tests. The results show that usable Al₂O₃–Al graded coatings could be fabricated. With a more continuous compositional gradient, the interface zone was more compact. The hardness and elastic modulus of Al₂O₃–Al graded coatings were less than those of Al₂O₃ coatings, but greater than those of Al₂O₃/Al coatings. After annealing at 773 K for 3 h, the hardness of Al₂O₃–Al graded coating showed a small increase. The residual stresses in Al₂O₃–Al graded coatings declined to about 0.3 GPa, compared with the 6.6 GPa for Al₂O₃ coating. The adhesion of Al₂O₃ was improved by deposition of Al or Al compositional gradient oxide layers. Copyright © 2011 John Wiley & Sons, Ltd.     

Characteristics of Plasma-Electrolytic Oxide Coatings Formed on Aluminum and Titanium in Electrolytes with Siloxane Acrylate and Particles of Vanadium,Boron, and Aluminum Oxides

It is shown that aqueous suspension-emulsion electrolytes containing sodium silicate, siloxane-acrylate emulsion, and dispersed particles of oxides are promising for direct synthesis by the plasma-electrolytic oxidation method of coatings with multicomponent composition on titanium and aluminum. The formation processes, composition, and structure of the coatings were studied in electrolytes with 1–4-μm particles of V₂O₅, B₂O₃, or Al₂O₃. The average content of metals and nonmetals of dispersed particles in the surface part of the coatings is ~1–2 at %. The coatings have a developed surface morphology and contain in the surface part up to 50–73 at % carbon.     

Preparation of nanoalumina/EPDM composites with good performance in thermal conductivity and mechanical properties

In this paper, nanoalumina (Al₂O₃) highly filled ethylene propylene diene monomer (EPDM) composites are prepared, and the mechanical (static and dynamic) properties and thermal conductivity are investigated systemically through various characterization methods. Furthermore, influences of in situ modification (mixing operation assisted by silane at high temperature for a certain time) with the silane‐coupling agent bis‐(3‐triethoxy silylpropyl)‐tetrasulfide (Si69) and stearic acid (SA) pretreatment on the nano‐Al₂O₃ filled composites are as well investigated. The results indicate that nano‐Al₂O₃ particles can not only perform well in reinforcing EPDM, but also improve the thermal conductivity significantly. Assisted by in situ modification with Si69, the mechanical properties (especially dynamic mechanical properties) of the nano‐Al₂O₃ filled composites are improved obviously, without influencing the thermal conductivity. By comparing to the traditional reinforcing fillers, such as carbon black (grade N330) and silica, in situ modified nano‐Al₂O₃ filled composites exhibit excellent performance in mechanical (static and dynamic) properties as well as better thermal conductivity, especially lower compression heat build‐up and better fatigue resistance. In general, our work indicates that nano‐Al₂O₃, as the novel thermal conductive reinforcing filler, is suitable to prepare rubber products serving in dynamic conditions, with the longer expected service life. Copyright © 2010 John Wiley & Sons, Ltd.     

Ni/Al2O3 catalysts for CO methanation: Effect of Al2O3 supports calcined at different temperatures

The correlation between phase structures and surface acidity of Al₂O₃ supports calcined at different temperatures and the catalytic performance of Ni/Al₂O₃ catalysts in the production of synthetic natural gas (SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al₂O₃ catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al₂O₃ supports were adjusted by calcining the commercial γ-Al₂O₃ at different temperatures (600–1200 °C). CO methanation reaction was carried out in the temperature range of 300–600 °C at different weight hourly space velocities (WHSV = 30000 and 120000 mL·g^?1·h^?1) and pressures (0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al₂O₃ supports due to the rapid decrease of the specific surface area and acidity of Al₂O₃ supports. Interestingly, Ni catalysts supported on Al₂O₃ calcined at 1200 °C (Ni/Al₂O₃-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al₂O₃-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures (600, 800 and 1000 °C). These findings would therefore be helpful to develop Ni/Al₂O₃ methanation catalyst for SNG production.     

Influence of powder-characteristics on the microstructure of ceramic plasma spray coatings

Summary The relationship between the properties of plasma spray powders and the resultant coating has been investigated. ZrO₂ powders, differing in grain size, state of agglomeration and morphology, have been used and coating properties such as microstructure, porosity, roughness, hardness, and wear resistance are described. Agglomerated powders cause high porosity, while sphericalized particles yield very dense layers. The homogeneity of an agglomerate is also responsible for the homogeneity of the microstructure of the coating. By selecting powders with defined characteristics it is possible to produce plasma spray coatings with defined properties; the microstructure of the layers can be varied over a wide range.