High thermal conductivity composites consisting of diamond filler with tungsten coating and copper (silver) matrix

Tungsten coatings with thickness of 5–500 nm are applied onto plane-faced synthetic diamonds with particle sizes of about 430 and 180 μm. The composition and structure of the coatings are investigated using scanning electron microscopy, X-ray spectral analysis, X-ray diffraction, and atomic force microscopy. The composition of the coatings varies within the range W–W₂C–WC. The average roughness, R _a, of the coatings’ surfaces (20–100 nm) increases with the weight–average thickness of the coating. Composites with a thermal conductivity (TC) as high as 900 W m⁻¹ K⁻¹ are obtained by spontaneous infiltration, without the aid of pressure, using the coated diamond grains as a filler, and copper or silver as a binder. The optimal coating thickness for producing a composite with maximal TC is 100–250 nm. For this thickness the heat conductance of coatings as a filler/matrix interface is calculated as G = (2–10) × 10⁷ W m⁻² K⁻¹. The effects of coating composition, thickness and roughness, as well as of impurities, on wettability during the metal impregnation process and on the TC of the composites are considered.     

Microstructure of high velocity oxy-fuel sprayed Ti2AlC coatings

The microstructure formation and phase transformations in Ti₂AlC-rich coatings deposited by High Velocity Oxy-fuel spraying of Maxthal 211^? powders is presented. High resolution electron microscopy analysis, using both scanning and transmission electron microscopy with energy dispersive spectrometry and energy filtering, combined with X-ray diffraction reveals that the coatings consist of Ti₂AlC grains surrounded by regions of very small TiC grains embedded in Ti _x Al _y . The composition of the Ti _x Al _y depends on its surrounding and varies with size and distribution of the adjacent TiC grains. Impact of spray parameters on coating microstructure is also discussed. Two spray parameters were varied; powder size distribution and flame power. They were found to greatly affect the coating microstructure. Increasing powder size and decreasing flame power increase the amount of Ti₂AlC, but produces thinner coatings with lower cohesion. Larger powder size will also decrease oxygen incorporation.     

Microstructure and property of Ni60A/WC composite coating fabricated by fiber laser cladding

Laser clad Ni60A/WC composite coating was fabricated on the surface of Q235 steel by using 6 kW fiber laser. The morphology, composition, and microhardness of composite coating were studied by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X‐ray diffraction (XRD), and micro‐hardness tester. The results show that in the process of fiber laser cladding Ni60A/WC composite coating, residual WC particles partially dissolve and react with other elements to form eutectics, which exists in the shape of lumpy, strip and spherical. The main structures of laser cladding are γ‐Ni, WC, W₂C, M₇C₃, M₂₃C₆ etc. From the hardness analysis, the average hardness of the composite coating is four times of the substrate.     

Synthesis of mesoporous hydroxyapatite using a modified hard-templating route

Mesoporous polycrystals of hydroxyapatite-calcium are synthesized via a modified hard-templating route. The structure properties of hydroxyapatite-calcium are characterized by means of X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and N₂ adsorption-desorption isotherms. Wide-angle X-ray diffraction and Fourier transform infrared spectroscopy measurements reveal that the crystalline grains consist of highly crystalline pure hydroxyapatite phases. Transmission electron microscopy results show that rod-like hydroxyapatite-calcium grains with an average diameter of about 100 nm long and about 20 nm wide are uniformly distributed, which are also observed with an average pore size of 2-3 nm. Based on N₂ adsorption-desorption isotherms investigation, the pore size, surface area and pore volume of mesoporous hydroxyapatite-calcium are 2.73 nm, 42.43 m² g⁻¹ and 0.12 cm³ g⁻¹, respectively.     

Homogenization of Carbides in Ni60/WC Composite Coatings Made by Fiber Laser Remelting

In the current study, the effect of laser remelting on homogenization of carbides in WC-reinforced Ni60 composite coatings was investigated. Ni60 + 50 wt% WC composite coatings were fabricated on the surface of Q550 steel by LDF4000-100 fiber laser device. First cladding layer was made by rectangle laser spot and then circular laser spot was utilized to remelt the coatings. Microstructure characteristics were investigated by optical microscope and scanning electron microscopy. Elemental distribution and phase constitution were analyzed by energy disperse spectroscopy and X-ray diffraction. The results showed that accumulation of residual WC particles was sufficiently eliminated under the effect of laser remelting. The irregularly shaped carbides in first cladding layer were transformed into well-distributed polygonal carbides by laser remelting. Statistical analysis indicated median size of reinforcement particles decreased from 35.40 to 5.62 µm. Microhardness of remelted region had a smooth profile and decreased by ?50 HV_0.1 than that of first cladding region. Homogenization of carbides in nickel composite coating was well realized by laser remelting.     

Microstructure of Nanostructured WC-Co Coating Prepared by Thermal Spraying

Nanostructured WC-Co coatings were produced with Atmospheric Plasma Spraying (APS) and Low Pressure Plasma Spraying (LPPS). Microstructure characteristics and phase compositions of the coatings were studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. The microstructure compositions were analyzed with EDS. During APS deposition the existence of oxygen causes the decarburization of the coating, and the coating was composed of melted area and the WC/12Co powder. Besides WC phase, there was W2C phase. However in the coating deposited by LPPS the content of oxygen was so low that there were a limit degradation of the WC/12Co powder. The coatings were made up of compact block and loosen porosity area. There were large quantities of nanostructure WC grains and a small quantity of microstructure WC grains presented in the coating. Besides WC phase, a little W2C and WC1-x or Co6W6C phases occured. Consideration of the characteristics of the highly porous, spherical-shell morphology of nano-WC/12Co power, heterogeneous melting and localized superheating of the power were two main factors which caused the microstructure and phase composition of nano-WC-Co coatings.     

Role of Al additions in wear control of nanocrystalline Mo(Si1−xAlx)2 coatings prepared by double cathode glow discharge technique

Abstract

Four kinds of nanocrystalline Mo(Si_1?xAl_x)₂ coatings with differing Al contents are prepared onto a Ti–6Al–4V substrates by a double cathode glow discharge apparatus. The microstructural features of the deposited coatings were characterised by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. These coatings are composed of the equiaxed C40–MoSi₂ grains with the average grain size of ～5 nm. Nano-indentation measurements indicated that the hardness H, elastic modulus E and the H/E or H³/E² ratio of the nanocrystalline Mo(Si_1?xAl_x)₂ coatings slightly increase with the increase in Al content. The tribological behaviour of the nanocrystalline Mo(Si_1?xAl_x)₂ coating sliding against a ZrO₂ ceramic ball at room temperature has been compared using a ball-on-disc type tribometer under unlubricated conditions. Experimental results showed that the specific wear rates of the nanocrystalline Mo(Si_1?xAl_x)₂ coatings decrease with increasing Al content and are dramatically reduced by more than 1–2 orders of magnitude over the uncoated Ti–6A1–4V. The enhancement of wear resistance of the nanocrystalline Mo(Si_1?xAl_x)₂ coatings by Al additions is correlated with the increased mechanical properties and the forming oxide layer by tribochemical reactions.     

One-pot synthesis and strong near-infrared upconversion luminescence of poly(acrylic acid)-functionalized YF<Subscript>3</Subscript>:Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript> nanocrystals

This paper describes the synthesis of new upconverting luminescent nanoparticles that consist of YF₃:Yb³⁺/Er³⁺ functionalized with poly(acrylic acid) (PAA). Unlike the upconverting nanocrystals previously reported in the literature that emit visible (blue-green-red) upconversion fluorescence, these as-prepared nanoparticles emit strong near-infrared (NIR, 831 nm) upconversion luminescence under 980 nm excitation. Scanning electron microscopy, transmission electron microscopy, and powder X-ray diffraction were used to characterize the size and composition of the luminescent nanocrystals. Their average diameter was about 50 nm. The presence of the PAA coating was confirmed by infrared spectroscopy. The particles are highly dispersible in aqueous solution due to the presence of carboxylate groups in the PAA coating. By carrying out the synthesis in the absence of PAA, YF₃:Yb³⁺/Er³⁺ nanorice materials were obtained. These nanorice particles are larger (∼700 nm in length) than the PAA-functionalized nanoparticles and show strong typical visible red (668 nm), rather than NIR (831 nm), upconversion fluorescence. The new PAA-coated luminescent nanoparticles have the pottential be used in a variety of bioanalytical and medical assays involving luminescence detection and fluorescence imaging, especially in vivo fluorescence imaging, due to the deep penetration of NIR radiation.      

Decarburization mechanisms of WC–Co during thermal spraying: Insights from controlled carbon loss and microstructure characterization

Decarburization behavior of WC–Co particles in terms of transformation of WC to W₂C and W, and formation of η and γ phases and microstructure evolution during plasma spraying have been systematically investigated in this study. The extent of the carbon loss of WC was tailored by either altering cooling conditions of substrate/pre-coating or spraying the particles into the media with different temperatures. It is revealed that loss of carbon of WC was alleviated by protection of Co during the coating formation stage. W₂C exhibits epitaxial growth on the WC substrates in perpendicular direction and forms a nearly complete shell around the WC particles. η phase was formed as a result of decarburization and diffusion of associated phases and is located around WC–Co splats with its crystals being in cross shape. The γ phase in rod-like shape with a size of 10–20 nm embeds within the binder Co and is clearly well separated from WC grains. Further decarburization-induced W was detected mainly in Co binder, being apart entirely from WC grains. The main advantage of Co for preventing decarburization in WC–Co particles is not associated with oxidation, but instead the diffusion-controlled carbon loss. These findings would facilitate fabrication of the WC-based cermet coatings with excellent mechanical properties in particular wear resistance for extreme wear applications.     

Influence of SiC, Si3N4 and Al2O3 particles on the structure and properties of electrodeposited Ni

The structure and properties of electrodeposited nickel composites reinforced with inert particles like SiC, Si₃N₄ and Al₂O₃ were compared. A comparison was made with respect to structure, morphology, microhardness and tribological behaviour. The coatings were characterized with optical microscopy, Scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD) technique. The cross-sectional microscopy studies revealed that the particles were uniformly distributed in all the composites. However, a difference in the surface morphology was revealed from SEM studies. The microhardness studies revealed that Si₃N₄ reinforced composite showed higher hardness compared to SiC and Al₂O₃ composite. This was attributed to the reduced crystallite size of Ni — 12 nm compared to 16 nm (SiC) and 23 nm (Al₂O₃) in the composite coating. The tribological performance of these coatings studied using a Pin-on-disk wear tester, revealed that Si₃N₄ reinforced composite exhibited better wear resistance compared to SiC and Al₂O₃ composites. However, no significant variation in the coefficient of friction was observed for all the three composites.     

Influence of Egyptian nanoilmenite/amorphous silica composite particles on the electrochemical and mechanical properties of cold galvanizing formulation coatings

In the present work, Egyptian ilmenite nanoparticles (FeTiO₃ NPs) were obtained with the average diameters of 20?nm by a direct solid-phase milling process and synthesized amorphous silica powder grains were processed to prepare a novel fabricated Egyptian nanoilmenite/amorphous silica composite (ENI/AS) particles. Flaky-like nature of ENI/AS and the spherical shape of Zn-dust particles were emphasized by scanning electron microscopic (SEM) micrographs. The nano features of ENI/AS particles were confirmed by transmission electron microscope (TEM) investigation. Various alkyd-based cold galvanizing coating formulations were modified using different uniformly dispersing amounts of the processed ENI/AS particles as a modifier to form some nanocomposite coatings. The electrochemical behavior of nanocomposite modified coated steel films in oil-wells formation water solution have been studied by both potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The mechanical properties of the coated films were studied through some coating tests as cross-cut adhesion, bend and impact to assert their application efficiency. Scanning electron microscope (SEM) technique was utilized to survey the protective film formed on the carbon steel surface by these modified coatings in formation water solution. The results of this study reinforced remarkable corrosion protection properties of ENI/AS modified cold galvanizing coating.     

Nanocrystalline TiO2 thin films for NH3 monitoring: microstructural and physical characterization

Nanocrystalline titanium oxide thin films have been deposited by spin coating technique and then have been analyzed to test their application in NH₃ gas-sensing technology. In particular, spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of titanium oxide thin films. The structure and the morphology of such material have been investigated by X ray diffraction, Scanning microscopy, high resolution electron microscopy and selected area electron diffraction. The X-ray diffraction measurements confirmed that the films grown by this technique have good crystalline tetragonal mixed anatase and rutile phase structure. The HRTEM image of TiO₂ thin film showed grains of about 50–60 nm in size with aggregation of 10–15 nm crystallites. Selected area electron diffraction pattern shows that the TiO₂ films exhibited tetragonal structure. The surface morphology (SEM) of the TiO₂ film showed that the nanoparticles are fine with an average grain size of about 50–60 nm. The optical band gap of TiO₂ film is 3.26 eV. Gas sensing properties showed that TiO₂ films were sensitive as well as fast in responding to NH₃. A high sensitivity for ammonia indicates that the TiO₂ films are selective for this gas.     

Structure and abrasive wear resistance of R6M5 steel-tungsten carbide composite coatings

Features of the structure formation, composition, and abrasive wear resistance of R6M5 steel-tungsten carbide (R6M5-WC) composite coatings have been studied as dependent on the WC content. The introduction of ～20 wt % WC into the hardening composition leads to an increase in the fraction of M₆C carbide (in the form of eutectic inclusions with average size ～5.9 μm at grain boundaries and dispersed ～0.25 μm particles in the volume of grains), while a large proportion of metastable austenite (～88 vol %) is still retained. The R6M5-WC coatings exhibit high abrasive wear resistance, which is ensured by the γ → α′ martensite transformation during friction and a muiltimodal size distribution of hardening particles.     

Synthesis and characterization of gold–polypyrrole film composite

Polypyrrole (PPy) coatings have potential applications in batteries, fuel cells, sensors, anti-corrosion coatings, and drug delivery systems. In this article, PPy film coating on the electrode of quartz crystal microbalance (QCM) was exposed to acidic aqueous HAuCl₄ solution. The reduction for gold ions took place and gold particles were produced at the film surface. The gold content at the PPy film was monitored by using QCM. The concentration of gold uptake increases as the original concentration of HAuCl₄ solution increases. The morphology of the film before and after the deposition of the gold particles was studied by the scanning electron microscopy coupled with energy dispersive X-ray spectrometry. The gold particles are of undefined shape and have diameters around 200–600 nm. However, the image of the composite powder shows that gold particles of sizes 100–120 nm are distributed over the surface of the polymer particles with some aggregation. Infrared spectroscopy and X-ray diffraction were used to characterize the composite.     

Cavitation erosion characteristics of a Fe–Cr–Si–B–Mn coating fabricated by high velocity oxy-fuel (HVOF) thermal spray

A Fe–Cr–Si–B–Mn coating was prepared by high velocity oxy-fuel (HVOF) thermal spray on the surface of 1Cr18Ni9Ti stainless steel. Microstructures of the coating were investigated by X-ray diffraction (XRD), optical microscopy (OM) and scanning election microscopy (SEM), and the cavitation erosion resistance of the coating was evaluated using a GB6383-86 standard method in fresh water and compared with hydro-machine material ZG06Cr13Ni5Mo martensite stainless steel. The coating consisted of a Fe–Cr-rich matrix and several kinds of borides, the former comprised both amorphous phase and nanocrystalline grains. The nanocrystalline grains with a size about 10–50 nm further formed into an agglomerate-like structure with an average size of 100–500 nm. The coating had a significantly higher microhardness (HV_0.21008) than the comparing material ZG06Cr13Ni5Mo (HV_0.2260), which resulted in greater weight losses of ZG06Cr13Ni5Mo at the whole cavitation erosion process. It was found that the mass loss began at the edges of the pores or the interface between un-melted or half-melted particles and the matrix in the coating, while the mass loss was initiated at the lath interface of martensite in the ZG06Cr13Ni5Mo. The experimental results indicate that the HVOF thermal spray is a promising method to prepare the cavitation resistance coating.     

High surface area neodymium phosphate nano particles by modified aqueous sol-gel method

Synthesis of nano rod shaped neodymium phosphate (NdPO₄) particles with specific surface area as high as 107 m²g⁻¹ and an average length of 50 nm with aspect ratio 5 was achieved using modified sol gel method. Crystallite size calculated from the X-ray diffraction data by applying Scherer equation was 5 nm for the precursor gel after calcination at 400 °C. NdPO₄ was first precipitated from neodymium nitrate solution using phosphoric acid followed by peptization using dilute nitric acid and further gelation in ammonia atmosphere. The calcined gel powders were further characterized by surface area (Brunauer-Emmet-Teller nitrogen adsorption analysis), Transmission electron microscopy, scanning electron microscopy, UV-vis and FT-IR analysis. Transmission electron microscopy confirms the formation of rod like morphology from the sol, gel and the calcined particles in nano size range. These particles could be compacted and sintered at as low as 1300 °C to a density of 98.5% (theoretical) with an average grain size of ∼1 μm.     

Preparation of zirconium diboride nanopowders in a sodium tetraborate ionic melt

Reactions between zirconium powder 10–15 μm in particle size and microcrystalline boron 10–20 μm in particle size in an Na₂B₄O₇ ionic melt have been studied at temperatures from 600 to 850°C and reaction times from 5 to 10 h. The results demonstrate that ZrB₂ forms starting at 750°C. According to scanning electron microscopy data, the ZrB₂ powder consists of particles 90–95 nm in average size. The crystallite size evaluated from X-ray diffraction data is 85 nm.     

Structural verification and optical characterization of SiO2–Au–Cu2O nanoparticles

In this paper, SiO₂–Au–Cu₂O core/shell/shell nanoparticles were synthesized by reducing gold chloride on 3-amino-propyl-triethoxysilane molecules attached silica nanoparticle cores for several stages. Cu₂O nanoparticles were synthesized readily with the size of 4–5 nm using a simple route of sol–gel method Then, they were clung to the surface of Au seeds. The morphology of the resultant particles was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Transmission electron microscopy images demonstrate growth of monodispersed gold seeds and Cu₂O nanoparticles in narrow size up to 10 nm and 5 nm, respectively. The presence of gold and Cu₂O coating was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and UV–Vis spectroscopy. Absorption spectroscopy shows considerably 40 nm blue shift in absorption edge for SiO₂–Au–Cu₂O nanostructure rather than SiO₂–Au core/shell nanoparticles.     

Microstructure, Magnetic and Electronic Transport Properties of Co–TiO2 Nanocomposite Films in Metal Matrix

In this work, Co–TiO₂ metallic composite films with a novel nanostructure have been electrodeposited in potentiostatic regime onto copper substrates, from a solution based on cobalt sulfate containing suspended TiO₂ nanoparticles, with magnetic stirring of the electrolyte. The effect of deposited film thickness on the morphology, microstructure, and composition of the films was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Functional properties (magnetic and electronic transport) of films with different thicknesses were studied in a view to find out the possibility for some technological applications. Nanocomposite Co–TiO₂ films contain three main phases: hcp Co crystalline grains (9–10 nm average size), TiO₂ nanoparticles (28 nm average diameter) embedded in Co metallic matrix and Co(OH)₂ adsorbed on the crystallite frontiers. The films display hysteresis (coercive field of 7.8÷11.9 kA/m) and significant values of magnetoresistance (with a maximum of ?59 % in the case of 0.07 μm film thickness). These properties can be qualitatively explained both by the elastic spin-dependent scattering of the conduction electrons at the interface between the magnetic Co matrix grains and the nonmagnetic regions, and by occurrence of antiferromagnetic coupling between Co crystallites, favored by inclusion in film of TiO₂ nanoparticles.     

工艺参数对EB-PVD制备YSZ涂层的影响

为探讨电子束物理气相沉积(EB-PVD)制备8 mol.%氧化钇稳定氧化锆(8YSZ)涂层过程中工艺参数对涂层致密性、表面粗糙度和晶粒择优取向生长的影响,利用扫描电镜、原子力显微镜和X射线衍射技术对涂层的上述性能进行了分析.分析结果表明,随沉积速率由750 nm/min下降至20 nm/min,YSZ涂层的晶粒逐渐聚合长大,晶粒之间的孔隙减少,涂层的气体扩散系数相应地由2.41×10-4cm4/(N·s)下降至6.56×10-5cm4/(N·s).YSZ涂层的表面粗糙度随靶基距的提高逐渐降低,涂层的晶体学取向随蒸汽粒子入射角的改变而改变,入射角为30°时(111)晶面具有平行于涂层表面排列的趋势,入射角为45°时(311)和(420)晶面具有平行于表面排列的趋势,而入射角为60°时(220)和(331)晶面具有平行于表面排列的趋势.