Modeling and simulation of the microstructural behaviour in thermal sprayed coatings

The purpose of the current work is the investigation of the mechanical behavior of thermal sprayed coatings to predict the influence of the application of compaction on the coatings. Due to the porosity and the poor surface quality of thermal sprayed coatings, an additional process step is necessary to compact the coating and to increase the surface quality, though leading to a complex deformation behavior of the coating. In a first step the microstructural evolution is investigated. Due to the fact that the experimental determination of the mechanical properties of a coating is quite complicated and cost-intensive, a general procedure is developed which generates the desired quantities for different coating composites from microstructural images which are compared to analytical mean-field homogenization solutions for elastic material behavior. The discussed thermal sprayed coatings are multiphase systems consisting of a metal-matrix composite with pores. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

基于分形维数的Ni-Co电刷镀层表面形貌分析研究

采用电刷镀技术获得了Ni-Co合金电刷镀层,借助于扫描电子显微镱观察得到了镀层的表面形貌图.通过改变镀液中Co离子含量的比例,使镀层中Co元素含量发生变化,从而使镀层表面形貌发生变化.利用盒维数的计算方法,计算出了不同Co元素含量的表面形貌分形维数.以分形维数作为衡量指标,研究了镀液中Co元素比例对镀层表面形貌的影响.     

FEM simulation of oxidation induced stresses in a simplified thermal barrier coating system

To study the behaviour of the complex failure mechanisms in thermal barrier coatings, a simplified model system is used to reduce the number of system parameters. The artificial system consists of a bond-coat material (fast creeping Fecralloy or slow creeping MA956) as the substrate with a Y₂O₃ partially stabilized plasma sprayed zircon oxide TBC on top and a TGO between the two layers. A FEM simulation was developed to calculate the stress distribution inside the coating system. The simulation permits the identification of compression and tension areas which are established by the growth of the oxide layer and the stresses which occur during the heating and cooling processes. Full thermal cycles, including heating from RT to 1000°C, dwelling for 2 hours and cooling to RT, were simulated. The stress distributions provide an insight into the possible failure mechanisms in the coating and allow to draw conclusions for optimizing real thermal barrier coating systems. It is shown that the failure mechanism depends on the creep properties of the bond-coat. Therefore, optimizing the creep properties may adjust lifetime of the whole coating system. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mechanical properties of cold sprayed Titanium and Nickel based coatings

Cold spray is an innovative coating technology. Very fine particles are accelerated, then sprayed on a substrate in condition very far from material melting. The unique mechanical properties experienced by the sprayed material are due to the severe plastic deformation acting during particle impact. In the present paper, the microstructural and mechanical behavior of Ti- and Ni-based nanocomposites coatings produced via cold spray are presented. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mechanical properties of carbon fibers coated with refractory carbides

The internal friction method has been used to investigate the protective function of barrier coatings of silicon and zirconium carbide. The effect of the thickness of the coating on the mechanical characteristics of carbon fibers and their oxidation resistance is examined. The optimal coating thickness is established. A surface hardening effect of the coatings has been detected.Voronezh Polytechnic Institute, Moscow. Translated from Mekhanika Polimerov, No. 3, pp. 536–538, May–June, 1976.     

Effect of silicon carbide coatings on the strength of carbon fibers

Conclusion The character of the effect of silicon carbide coatings on the strength of carbon fibers is a function of the strength of the coating, which decreases with an increase in its thickness. The results obtained permit hoping for a significant increase in the strength of fibers by application of high-modulus coatings. It can be attained as a result of increasing the critical value of the coating thickness due to optimization of the conditions of preparation, which will improve the structure of the articles.Translated from Mekhanika Kompozitnykh Materialov, No. 4, pp. 604–608, July–August, 1988.     

Analysis of the Adhesion and Adhesion Strength of Two-Layer Polymer Films and Coatings

The formation of adhesion bonds during the creation of two-layer polymer films and coatings capable of acid–base interaction is considered. The coatings are obtained from polymer solutions, and the second layer is formed from the polymer solutions and their mixtures on a hard polymer coating. As a result of absorption by the coating of a considerable amount of solvents (to 14%), polymer macrochains are able to approach one another at a distance necessary for the formation of acid–base (hydrogen) bonds and a transition layer. The polar component of the work of adhesion is equal to about 50% of the whole work W _a. There is no interrelation of the thermodynamic work W _a between the films and the work of their separation into layers. The main part of the external work upon the separation is spent (if strong donor–acceptor bonds are formed) for extracting the segments and macrochains of polymers out of the films.     

Structure and Properties of Electrodeposited Composite Metal–Nanodisperse Inorganic Compound Coatings

By using the electrodeposition method, composite Sn-inorganic coatings have been obtained. As the inorganic compounds, ultrafine PbMo₆S₈, NbC_xN_y, Ti_xN_y, and Ti_0.63Nb_0.34C_0.38N_0.58 powders were utilized. The Sn–PbMo₆S₈ coatings containing 28-88 wt.% PbMo₆S₈ were superconductive. The highly electroconductive Sn–NbC_xN_y coatings containing 1-88 wt.% of the disperse phase and the Sn–Ti_xN_y coatings with 42-70 wt.% Ti_xN_y were structurally stable at a low temperature (–50°C), solderable, and corrosion resistant on copper. The formation of the structure of the coatings is determined by the electrolyte composition, the cathode current density during the electrolysis, and the codeposition of the disperse phase. By electrodeposition of the chromium carbonitride Cr₃C_1.6N_0.4, in the presence of H₄P₂O₇ in an CrO₃-based electrolyte, mat composite Cr–Cr₃C_1.6N_0.4 coatings with 6.8 wt.% Cr₃C_1.6N_0.4 were obtained, which had a finely uneaven surface structure. Such surfaces are needed in the cases where lubricants are used.     

Effect of polymer molecular weight on its reaction with nonporous and porous fillers

The effect of polymer molecular weight (using polyethylene and polyisobutylene) on the formation of polymer contact with the surface of porous and nonporous fillers has been studied. It has been shown that the extent of coating of a nonporous surface by polymer does not depend on polymer molecular weight, but the extent of coating of a porous surface is larger, the lower the molecular weight of the polymer; this is explained by a selective adsorption of macromolecules of lower molecular weight on the porous filler from the polymer melt.     

Determining Mechanical State of the Body – Multilayer Coating System

This paper suggests an effective approach, essentially simplifying determining mechanical state of bodies with thin multilayer coatings. It is based on the modeling of such coatings by thin shells with appropriate geometrico-mechanical properties of a coating. In such an approach, the influence of thin coatings on the mechanical state of the body - multilayer coating system is described by special generalized boundary conditions. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mass-spectrometric investigation of solid lubricating coatings subjected to friction in a deep vacuum

The life of solid lubricating coatings of the VNII NP type, based on molybdenum disulfides and various binders, has been experimentally investigated under deep vacuum conditions (10^–8–5 · 10^–9 torr) together with the composition of the gas released in the friction process. It is shown that both under atmospheric conditions and in a deep vacuum the life of the coatings depends on the chemical nature of the film-former. The depth of the vacuum also has an important influence on the life of the coatings, both the mechanism and the end result of this effect depending to a large extent on the physicochemical properties of the bind. On the interval 10^–1–10^–2 torr there is a sudden change in the life of the coating.Physicotechnical Institute of Low Temperatures, Academy of Sciences of the Ukrainian SSR, Khar'kov. Translated from Mekhanika Polimerov, No. 6, pp. 1070–1075, November–December, 1970.     

泡沫覆盖层对水下爆炸气泡射流防护机理缩比试验研究

水下爆炸会对水中结构物造成严重威胁。柔性覆盖层或夹层板能够降低水中结构物水下爆炸冲击响应，因此成为研究的热点。以往的研究多集中于覆盖层对冲击波的防护机理，适用于较远距离的水下爆炸情况。近距离水下爆炸除了冲击波外，爆炸气泡溃灭时产生的朝向结构物的高速水射流更为致命。该文针对这种情况，基于量纲原理，推导缩比相似关系，通过缩比模型水下爆炸试验发现了覆盖层表面空化微气泡群对爆炸气泡形成高速水射流过程产生干扰，提出了泡沫覆盖层钢板水下爆炸气泡射流防护机理。     

A study of the life of alkyd coatings

The effect of the conditions of formation and aging on the life of alkyd coatings is studied. It is shown that the life of alkyd coatings aged under various conditions can be expressed by the general equation =Ae^–ax The relationship between the life of alkyd coatings and curing temperature is linear. It is observed that the conditions of aging have no effect on the rupture energy or ₀, but cause a substantial change in the distribution of the lines =f(1/T_f). Cross-linkage of alkyd coatings due to the action of heat, light, and moisture, under various conditions of aging, is accompanied by an increase in rupture energy with increase in the internal stresses.Mekhanika Polimerov, Vol. 1, No. 3, pp. 68–76, 1965     

Mathematical modelling of layered contact mechanics of cam–tappet conjunction

The paper briefly introduces a fast converging mathematical model to predict the peculiarities of the non-conforming contact between an infinitely long cylinder and a coated elastic substrate. The proposed method is then integrated into a multi-physics analysis of the valve train system of a racing type internal combustion (IC) engine. Due to relatively high loads and speeds experienced, particularly in the cam–tappet contacts, hard wear resistant coatings are used, which greatly influence the contact mechanics performance. Results indicate that the layer thickness is the determining factor in contact characteristics, which alters during the cam cycle. Therefore, for optimal performance coatings of non-uniform thickness should ideally be applied to the circumference of the cam rather than the usual coating of the tappet surface with a given thickness.     

快变海底和自由表面流共振生成的弱非线性Stokes波

运用WKBJ型摄动逼近法,对环境流同沙纹海底共振产生的自由表面水波的非线性效应进行了研究。沙纹海底由缓变平均水深部分和快变海底部分叠加构成。根据对快变海底波长的不同选取,可以相应地激发环境流同非平整海底的同步共振、超谐波共振和次谐波共振,由此产生自由表面波运动。对次谐波共振进行了详细考察。对于定常流自治动力系统,对可能出现的非线性各种稳态及其稳定性进行了探讨。假如环境流具有一个小振动分量,动力系统成为非自治的,则将发生混沌现象。     

Nanocrystalline Diamond Coatings

Carbon—in the form of diamond coatings (nanocrystalline diamond—NCD) on suitable substrates—has attractive properties for biomedical applications. The excellent chemical inertness of NCD films makes them a promising material for medical implants, cardiovascular surgery and for coating of certain components of artificial heart valves.

The medical applications of carbon films impose some special requirements on their quality, purity, phase content and the state of the surface. Of particular importance is the smoothness of the surface and good adhesion of the coatings to the substrate. We have investigated carbon films which were synthesized by Radio Frequency Plasma Chemical Vapour Deposition (RF–PCVD).

The specimens obtained have been tested to show their structure and their biological, mechanical and chemical resistance. Additional investigations of the NCD films were carried out by micro-X-ray spectroscopy, Raman spectroscopy, AFM, Auger spectroscopy, corrosion tests, breakdown tests and clinical investigations. Nanocrystalline diamond (NCD) layers obtained by a new method of RF dense plasma CVD onto AISI-316L steel used in surgery were investigated to determine their suitability as biomaterials.     

Long Nonlinear Waves in Resonance with Topography

The evolution of periodic long surface waves over a periodic bottom topography resonant with the waves is studied. Coupled Korteweg–de Vries equations are derived and describe the evolution in terms of interaction between right- and left-traveling waves. The coupling arises from the cumulative effect of wave scattering. We discuss the various conserved quantities of the system and compute solutions for the initial value problem and for the time-periodic problem of fluid "sloshing" in a tank. Some three-dimensional extensions are discussed.     

Effect of fillers and solvents on the properties of polystyrene coatings

The mechanism of coating formation from solutions of atactic polystyrene in xylene and carbon tetrachloride has been investigated. It has been established that, as the filler content increases, in coatings formed from polystyrene solutions containing an evaporating solvent the growth of the internal stresses and the thermophysical characteristics is characterized by similarity of slope, as distinct from the case of coatings obtained from systems containing a polymerizing solvent. It is shown that the nature of the solvent has an important effect on the character of the interaction at the polymer—filler interface and on the structure and properties of the coatings.Kucherenko Central Scientific-Research Institute of Structural Design. Institute of Physical Chemistry, AS USSR, Moscow. Translated from Mekhanika Polimerov, Vol. 4, No. 6, pp. 1127–1129, November–December, 1968.     

Theory of vibration-damping polymeric coatings

Conclusions 1. An approximate method for calculating the characteristics of vibration-damping polymeric coatings of complex construction, based on equations of the theory of multilayer plates and shells, has been developed.2. The dimensionless parameters of the theory of multilayer plates and shells, g and h/r, are the basic quantities which determine the effectiveness of a damping coating.3. An increase in number of layers in the coating, while preserving the overall thickness of the packet and an assigned ratio between the thicknesses of the polymeric and rigid layers, exerts only a small effect on the effectiveness of the coating.Moscow Power Institute. Translated from Mekhanika Polimerov, No. 2, pp. 269–276, March–April, 1978.     

Rotational waves generated by current‐topography interaction

We study nonlinear free‐surface rotational waves generated through the interaction of a vertically sheared current with a topography. Equivalently, the waves may be generated by a pressure distribution along the free surface. A forced Korteweg–de Vries equation (fKdV) is deduced incorporating these features. The weakly nonlinear, weakly dispersive reduced model is valid for small amplitude topographies. To study the effect of gradually increasing the topography amplitude, the free surface Euler equations are formulated in the presence of a variable depth and a sheared current of constant vorticity. Under constant vorticity, the harmonic velocity component is formulated in a simplified canonical domain, through the use of a conformal mapping which flattens both the free surface as well as the bottom topography. Critical, supercritical, and subcritical Froude number regimes are considered, while the bottom amplitude is gradually increased in both the irrotational and rotational wave regimes. Solutions to the fKdV model are compared to those from the Euler equations. We show that for rotational waves the critical Froude number is shifted away from 1. New stationary solutions are found and their stability tested numerically.