Ni-WC composite coatings by carburizing electrodeposited amorphous and nanocrystalline Ni-W alloys

In situ formation of tungsten carbide in the matrix of FCC nickel has been achieved by carburizing of the electrodeposited Ni-W alloy coatings. The size of the carbide particles ranges between 100 and 500 nm. The carbide phase is also present in the form of very small precipitates inside the nickel grains. The size of such precipitates is between 10 and 40 nm. The carburizing environment was created by introducing a flowing mixture of vaporized 95.5% alcohol (0.25 ml/min, liquid) and argon (0.5 L/min, gas) into the carburizing furnace. Supersaturated nature of electrodeposited amorphous and nanocrystalline alloys, in addition to high diffusivity, have been attributed for the formation of carbide phase in the deposits at a temperature range of 700-850 °C. The carbide-metal interface is clean and the composite coatings are compact. Hardness values up to about 1100 KHN are achieved. Hardness increases with tungsten content and carburizing temperature.     

Ultrasonic-assisted electrodeposition of Ni/diamond composite coatings and its structure and electrochemical properties

Ni/diamond composite coatings have been synthesized by ultrasonic-assisted electrodeposition in a Ni electroplating bath containing diamond nanoparticles. The influences of current density and ultrasonic agitation on the coating composition, morphology, topography, phase structure, and electrochemical characteristics of the electrodeposits were evaluated. Ultrasonic agitation was provided using an external ultrasonic bath at a frequency of 40 kHz and acoustic power of 300 W. Coating samples were also prepared under magnetic stirring for comparison with the ultrasonic-assisted deposits. This work reveals that the diamonds have been incorporated and evenly distributed in the composites. The coatings exhibit dense, granular like morphology with pyramid-like grains. As current density increases, the diamond amount of ultrasonic-assisted electrodeposits first increased to maximum of 11.4 wt% at 3 A dm⁻² and then decreases to 9.9 wt% at 5 A dm⁻², and the RTC of the preferred orientation (2 0 0) plane increases from 76.3% up to 93.4%. The crystallite size was 60–80 nm and the R_a of the magnetic and ultrasonic agitations were 116 nm, 110 nm, respectively. The maximum R_p of 39.9, 50.3 kΩ cm² was obtained at 4 A dm⁻² when respectively immersed 30 min and 7 days, illustrating the best corrosion resistance of the coatings of 4 A dm⁻². The effects of mechanical and ultrasonic agitations on the mechanism of the co-electrodeposition process were both proposed. The incorporation of diamond particles enhances the hardness and wear-resisting property of the electrodeposits. The ultrasonic-assisted electrodeposited Ni/diamond coating has better corrosion resistance than that prepared under mechanical stirring conditions.     

Tribological coatings with a chromium-based composite structure obtained by reactive deposition in vacuum

The peculiarities inherent to the chemical and phase compositions, microstructure, and tribological behavior of Cr-O, Cr-C-O, Cr-C-H and Cr-C-N-H coatings, obtained by plasma-assisted physical vapor deposition in a chemically active gas atmospheres (activated reactive deposition and magnetron sputtering methods), have been studied. It has been demonstrated that all coatings have a micro- and/or nanocomposite structure comprising nanoscale chromium-based domains, as well as chromium oxide, carbide and nitride phases with different stoichiometries. The tribological properties of the coatings investigated in a broad temperature range under unlubricated friction contact conditions, as well as their correlation with microstructures and reactive-deposition technology parameters, are discussed.     

Nonlinear properties of two-phase composite films with a fractal structure

Inhomogeneous two-phase conducting films whose structure is intermediate between three-and two-dimensional configurations are discussed. The longitudinal film size exceeds the correlation length, and its thickness is less than the correlation length. In the case of weak nonlinearity, we found dependences of the film resistivity on the concentration and size of conducting particles, as well as on the film thickness, in the framework of a percolation approach.     

Magnetic properties of nanocrystalline composite in the Nd--Fe--B system

Using ⁵⁷Fe Mössbauer spectroscopy, X-ray diffraction and magnetization measurements, magnetic properties of melt-spun Nd_4.5Fe₇₇B_18.5 ribbon have been investigated after the annealing treatments which make nanocrystalline composite from the as-prepared amorphous state. Specimen ribbon which shows coercivity and is suitable for a permanent magnet consists of the mixture of Fe₃B and Nd₂Fe₁₄B. Relative fraction of these phases in the ribbon have been determined.     

纳米GaSb-SiO2复合薄膜的非线性光学特性

利用射频磁控共溅射的方法制备出纳米GaSbSiO2镶嵌复合薄膜.用Cary5E分光光度计分析研究了复合薄膜的室温透射光吸收特性.用Z扫描方法测量了复合薄膜在6328nm处大的双光子吸收系数β≈0082mW,非线性折射率γ≈376×10-9m2W及非线性系数χ(3)≈784×10-9esu. 关键词： 纳米GaSb 双光子吸收 光学非线性     

Production, structure, and microhardness of nanocrystalline Ni-Mo-B alloys

Radiography, differential scanning calorimetry, luminescence and high-resolution electron microscopy are used to study the production, nanocrystalline structure, stability, and microhardness of alloys from the Ni-Mo-B system containing from 27 at. % to 31.5 at. % Mo and 10 at. % B. All studies of these alloys indicated that annealing at 600 °C leads to the creation of a granular phase consisting of FCC nanocrystallites with average grain sizes of 15–25 nm, depending on the chemical composition of the alloy. Annealing these nanocrystalline samples isothermally at a temperature of 600 °C has no appreciable effect on the grain size. Structurally, the nanocrystalline phase consists of grains of an FCC solid solution of Mo and B in Ni, dispersed in an amorphous matrix that isolates them from one another. The lattice parameters of the FCC nanocrystallites depend on the alloy composition and the duration of their isothermal anneal. Within this latter time, molybdenum and boron atoms diffuse from the FCC solid-solution lattice into the surrounding amorphous matrix. The stability of the nanocrystalline structure is determined by the thermal stability of the amorphous matrix, whose crystallization temperature increases with the isothermal annealing time due to enrichment by boron and molybdenum. As the structure forms, the alloy becomes harder as the nanocrystalline grains grow in size. This relation between hardness and grain size, which is opposite to the Hall-Petch law, is explained by hardening of the amorphous matrix due to changes in its chemical composition. Fiz. Tverd. Tela (St. Petersburg) 40, 10–16 (January 1998)     

Development and evaluation of electroless Ag-PTFE composite coatings with anti-microbial and anti-corrosion properties

Electroless Ag-polytetrafluoroethylene (PTFE) composite coatings were prepared on stainless steel sheets. The existence and distribution of PTFE in the coatings were analysed with an energy dispersive X-ray microanalysis (EDX). The contact angle values and surface energies of the Ag-PTFE coatings, silver coating, stainless steel, titanium and E. coli Rosetta were measured. The experimental results showed that stainless steel surfaces coated with Ag-PTFE reduced E. coli attachment by 94-98%, compared with silver coating, stainless steel or titanium surfaces. The anti-bacterial mechanism of the Ag-PTFE composite coatings was explained with the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The anticorrosion properties of the Ag-PTFE composite coatings in 0.9% NaCl solution were studied. The results showed that the corrosion resistance of the Ag-PTFE composite coatings was superior to that of stainless steel 316L.     

Magnetic properties and structure of the nanocrystalline Gd-Ti-Ge intermetallic compound

This paper reports an experimental study of the magnetization processes and structure of the Gd-Ti-Ge compound in the initial coarse-grained state and a nanostructured state obtained under torsion at a high quasihydrostatic pressure. It is established that in a nanocrystalline sample, the magnetic ordering temperature is 30 K lower, the coercive force is eight times higher, and the magnetization is 3.7 times lower than their respective values in a coarse-grained sample. The observed changes in the magnetic properties are shown to be related primarily with the conversion of a part of the initial phase with the CeScSi-type lattice to a CeFeSi-type weakly magnetic phase. The effect of structural defects and of partial disorder on the magnetic characteristics of the compound are also discussed.     

Comparison of anti-corrosion properties of polyurethane based composite coatings with low infrared emissivity

Four polyurethane resins, pure polyurethane (PU), epoxy modified polyurethane (EPU), fluorinated polyurethane (FPU) and epoxy modified fluorinated polyurethane (EFPU), with similar polyurethane backbone structure but different grafting group were used as organic adhesive for preparing low infrared emissivity coatings with an extremely low emissivity near 0.10 at 8-14 μm, respectively. By using these four resins, the effect of different resin matrics on the corrosion protection of the low infrared emissivity coatings was investigated in detail by using neutral salt spray test, SEM and FTIR. It was found that the emissivity of the coatings with different resin matrics changes significantly in corrosion media. And the results indicated that the coating using EFPU as organic adhesive exhibited excellent corrosion resistance property which was mainly attributed to the presence of epoxy group and atomic fluorine in binder simultaneously.     

Strength and plasticity of nanocrystalline metals with a bimodal grain structure

Using dislocation-kinetics equations, the structural factors are discussed that determine the strength and plastic properties of nanocrystalline metals with a bimodal grain structure containing not only nanograins but also a certain volume fraction of micron-sized grains. It is found that the plasticity (uniform strain) of nanocrystalline metals with a bimodal structure is significantly higher than that of a unimodal structure and the strength remains at the same high level. This improvement can be attained for a certain combination of factors, such as the relation between the grain sizes, the ratio of the volume fractions of nano-and micrograins in the bimodal structure, and the parameter determining the efficiency of grain boundaries as dislocation sources.     

Structure and properties of the Ti-Si-N nanocrystalline coatings synthesized in vacuum by the electroarc method

Phase composition, defect substructure, and mechanical properties of the Ti-Si-N coating deposited on metal and ceramic-metal substrates by electroarc sputtering of the Ti-Si composite cathode in an ionized nitrogen atmosphere are investigated by the methods of modern materials science. It is established that coatings so formed with a thickness of ∼1–3 μm are superhard (H_v ∼ 50 GPa), and have the nanocrystalline structure (with crystalline sizes D = 7 nm) based on titanium nitride δ-TiN. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 46–51, February, 2007.     

Electrodeposition and tribological properties of Ni-SrSO4 composite coatings

Ni-SrSO₄ composite coatings were electrodeposited on superalloy Inconel 718 from a Watts electrolyte containing a SrSO₄ suspension. Ni-SrSO₄ coatings were investigated by scanning electron microscope, microhardness tester, and friction and wear tester in sliding against a bearing steel ball under unlubricated condition. The incorporation of SrSO₄ into Ni matrix increases the microhardness of electrodeposited coatings. Ni-SrSO₄ composite coating exhibits a distinctly low friction coefficient and a small wear rate as contrasted with pure Ni coating and the substrate. The effect of SrSO₄ particles on microstructure and tribological properties of Ni-SrSO₄ composite coatings is discussed.     

Molecular structure and optical properties of PTFE-based nanocomposite polymer-metal coatings

The molecular organization of polytetrafluoroethylene (PTFE) thin coatings with incorporated Ag, Cu, and Mo nanoparticles that are deposited from an active gas component has been studied. Polyethylene terephtalate film coated by aluminium served as a substrate. The active gas component was produced by electron beam dispersion of original components in vacuum. The effect of metal particle size and its nature on the molecular structure of coatings have been investigated. Dichroism of thin nanocomposite coatings has been examined by polarized Fourier transform infrared spectroscopy using an attenuated total reflection unit. The morphology of the coatings has been analyzed by transmission (TEM), atomic-force (AFM), and scanning electron (SEM) microscopy. It is found that introduction of a metal (Ag or Cu) yields oriented layers at a lesser efficient thickness of a coating. The surface plasmon resonance of such structures was studied by measuring optical absorption of the coatings in the ultraviolet and visible ranges. The results show that the composite coatings containing Ag clusters are diameter less than 30 nm and absorb within the short-wave range from 400 to 550 nm.     

Electrodeposition and properties of Zn-nanosized TiO2 composite coatings

Nanosized TiO₂ particles were prepared by sol-gel method. The TiO₂ particles were co-deposited with zinc from a sulphate bath at pH 4.5 using electrodeposition technique. The corrosion behavior of the coatings was assessed by electrochemical polarization, impedance, weight-loss and salt spray tests. Wear resistance and microhardness of the composite coating was measured. The smaller grain size of the composite coatings was observed in the presence of TiO₂ and it was confirmed by the images of scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques.     

Preparation and properties of electroless Ni-P-SiO2 composite coatings

Dispersible SiO₂ nanoparticles were co-deposited with electroless Ni-P coating onto AISI-1045 steel substrates in the absence of any surfactants in plating bath. The resulting Ni-P/nano-SiO₂ composite coatings were heat-treated for 1 h at 200 °C, 400 °C, and 600 °C, respectively. The hardness and wear resistance of the heat-treated composite coatings were measured. Moreover, the structural changes of the composite coatings before and after heat treatment were investigated by means of X-ray diffraction (XRD), while their elemental composition and morphology were analyzed using an energy dispersive spectrometer (EDS) and a scanning electron microscope (SEM). Results show that co-deposited SiO₂ particles contributed to increase the hardness and wear resistance of electroless Ni-P coating, and the composite coating heat-treated at about 400 °C had the maximum hardness and wear resistance.     

Misfit disclination dipoles in nanocrystalline films and coatings

A theoretical model is proposed for describing the special physical micromechanism of misfit stress relaxation in nanocrystalline (NC) films and coatings. According to this model, under certain conditions, grain boundary sliding occurs in NC films and coatings, which is accompanied by the formation of an ensemble of disclination dipoles (rotational defects). These dipoles produce elastic stress fields, which partially compensate misfit stresses in NC films and coatings. Using the proposed model, it is shown that the nucleation of disclination dipoles in a film (coating) can significantly decrease the total energy of the film/substrate composite for the AlN/6H-SiC and GaN/6H-SiC systems over a wide range of structural parameter values.     

Hardness and microplasticity of nanocrystalline and amorphous calcium phosphate coatings

The hardness of thin (1.0–4.0 μm) hydroxyapatite coatings with different structures (nanocrystalline, amorphous-crystalline, and amorphous) grown by rf magnetron sputtering on Ti and Si plates has been studied using the nanoindentation method. All the grown structures are characterized by the strain which has reversible and irreversible components. The hardness of nanocrystalline coatings (about 10 GPa) corresponds to the average hardness of hydroxyapatite single crystals. The structure of nanocrystalline coatings in the indentation zone and outside it has been investigated and changes in the structure under the indenter have been revealed using high-resolution transmission electron microscopy. From a comparison of the hardnesses of coatings with different structures and based on an analysis of the intragranular structure, it has been assumed that the plastic deformation occurs according to a dislocation-free mechanism. The plastic deformation is interpreted in terms of the cluster representation of the hydroxyapatite structure and amorphous calcium phosphates of the same elemental composition and cluster-boundary sliding during the deformation.     

Effects of Co and W alloying elements on the electrodeposition aspects and properties of nanocrystalline Ni alloy coatings

Depending on deposition current density and alloying elements, various types of surface structure (surface morphology and grain orientation) were observed for Ni and Ni alloy nanocrystalline coatings. It was found that the variation of surface morphology with current density is in a good agreement with the variation of grain orientation. An increase in the current density produced larger grains and also reduced the charge transfer resistance and growth inhibition intensity which may change the surface structure of the coatings. For Ni coatings, the effect of surface structure on the corrosion resistance was detected to be superior to that of grain size. In the case of Ni-Co coating and at different deposition current densities, Co content and surface structure were recognized as the major factors influencing the corrosion resistance. Surface structure was also a more important factor determining the corrosion resistance of Ni-W coatings. In Ni-Co-W coatings, surface structure and grain size of the coatings were found to be independent of deposition current density. This is believed to be due to the simultaneous contrary effects of Co and W elements.     

Nb含量对FeSiBCuNb系铁基纳米晶合金结构和磁学性能的影响

为模拟Nb含量对FeSiBCuNb系铁基纳米晶合金结构和磁学性能的影响,采用Amorphous模块构建了Fe_88-xSi₉B₂CuNb_x(x=1,3,5,7)的硬球密剁模型,通过分子动力学方法进行弛豫,淬火以及退火处理,得到了Fe_88-xSi₉B₂CuNb_x(x=1,3,5,7)铁基纳米晶合金结构.基于第一性原理的计算方法,分析了不同Nb含量的铁基纳米晶合金的晶体结构和磁学性能.结果表明:随着Nb含量的增加,体系的晶格常数和体积都有所增大,导电性减小,磁矩不断减小,并且Fe的3d轨道是体系磁矩的主要贡献者,Nb元素对体系非晶化的形成有一定的作用.