Proposal for photothermal characterization of boundaries between layer and substrate

The accurate measurement of frequency dependent photothermal phase angle curves allows the characterization of the boundary layer between substrate and coating. Regarding the measurable quantities phase extremum and the ratio of the abscissa for the zero crossing and the extremum we can classify the boundary type as a jump in material properties, as a delamination or as a diffusion zone between substrate and coating.     

Scratch adhesion testing of hard coatings

The scratch test for adhesion is reviewed as the only method currently available for testing thin, hard and well-adhering coatings such as TiC on steel or cemented carbide substrates. The critical load, mode of coating removal and acoustic signals are discussed. It is found that the combination of acoustic signal with microscopic observations can indicate whether failure occurs following a cohesive or an adhesive mode. The critical loads increase with increasing coating thickness in a manner which is a characteristic of the coating-substrate combination being studied. Critical loads are higher for harder tougher substrate materials; they also appear to depend on the elastic modulus and the coefficient of friction of the coating itself.     

HVOF金属陶瓷涂层的冲蚀失效行为研究现状

超音速火焰喷涂具有粒子飞行速度高、涂层质量好、沉积速度快、材料选择性好以及与基体的结合强度高等优点。冲蚀是水轮机过流部件、轮船螺旋浆、泥浆泵及钻杆等的主要失效形式之一。HVOF技术制备的金属陶瓷涂层因其能显著提高金属零部件的耐冲蚀性能而受到广泛应用。本文对国内外HVOF喷涂金属陶瓷涂层的冲蚀失效行为进行综述,系统归纳了冲蚀颗粒粒径、冲蚀速度、攻角等外部因素及涂层的结合强度、孔隙率、涂层颗粒尺寸、碳化物颗粒的大小等内部因素对HVOF喷涂金属陶瓷涂层冲蚀失效行为的影响机制。并指出综合评价外部服役条件和自身性能参数对涂层冲蚀失效行为的作用机理是本领域今后研究的重点方向之一。     

Diamond films deposited on WC-Co substrates by use of barrier interlayers and nano-grained diamond seeds

Results on the structure, composition and properties of diamond films deposited onto WC-Co cemented carbides via special multilayer barrier interlayers preliminary seeded by nano-grained diamond particles are presented. The barrier interlayers comprise a layer adjacent to the substrate, which completely prevents substrate decarburization and Co diffusion from the substrate, and a diamond-bonding layer needed to obtain an enhanced adhesion of the PACVD diamond coating. Preliminary seeding the barrier interlayers with nano-grain diamond particles by use of a laser ablation technique allows a fine-grained, uniform and highly adherent diamond coating of high quality to be deposited by use of a conventional PACVD technique. Results on the nature of the interaction between the diamond nano-grained seeds and barrier interlayer are also presented.     

热冲击作用下基底/涂层结构的应力分析及结构优化

分析了基底/涂层结构的动态热应力, 并对涂层的厚度进行了优化。采用Fourier 变换法,在L aplace 域内求解了问题的控制微分方程, 然后利用界面连续条件、边界条件以及L ap lace 数值反演, 得出了结构中的动态温度场和热应力场。数值算例表明, 加热速度对结构中的最大热应力、破坏模式以及涂层厚度的优化值都会产生影响。      

Indentation modulus extrapolation and thickness estimation of ta-C coatings from nanoindentation

Coatings used in tribological applications often exhibit high hardness and stiffness to achieve high wear resistance. One coating characterization method frequently used is nanoindentation which allows the determination of indentation hardness and indentation modulus among other material properties. The indentation modulus describes the elastic surface behavior during indentation and is, among hardness, a direct indicator for wear resistance. To obtain the true indentation modulus of a coating, it must be measured with varying loads and then extrapolated to zero load. Current recommendation of the standard ISO 14577-4:2016 is a linear extrapolation which fits poorly for nonlinear curves. Such nonlinear curves are commonly found for high hardness mismatches between coating and substrate, for example, superhard tetrahedral amorphous carbon coatings (ta-C) on a steel substrate. In this study, we present a new empirical fit model, henceforth named sigmoid. This fit model is compared to several existing fit models described in the literature using a large number of nanoindentation measurements on ta-C coatings with wide ranges of indentation modulus and coating thickness. This is done by employing a user-independent and model agnostic fitting methodology. It is shown that the sigmoid model outperforms all other models in the combination of goodness of fit and stability of fit. Furthermore, we demonstrate that the sigmoid model’s fit parameter directly correlates with coating thickness and thus allows for a new approach of determining ta-C coating thickness from nanoindentation.

     

Sliding wear evaluation of various coating processes on AISI 52100 and M 50 steels

Abstract

Lubricated sliding wear tests were carried out on various surface coatings that were deposited on AISI 52100 and M50 steel substrates. The coatings include titanium nitride (TiN) deposited via an ion plating process, an electroplated chromium termed thin dense chrome (TDC), and a vanadium carbide (VC) deposited via the Toyota diffusion (TD) process. The tests were carried out using a synthetic turbine oil at one sliding speed and stepwise loading until catastrophic failure of the coating occurred. Friction coefficients were measured throughout the test interval, which showed that the vanadium carbide coating produced the lowest values (less than 0·055). Furthermore, this coating process had the greatest load carrying capacity, followed by the ion plated TiN on the M 50 substrate. Optical and scanning electron microscopy revealed that each coating process exhibited a different wear mode. In the TiN and VC coatings, polishing occurred along with the formation of cracks perpendicular to the sliding direction. Portions of the TiN coating spalled off the substrate via a delamination process. The TDC coating exhibited only a polishing wear mode.

MST/1691     

Evaluation of residual stresses in PVD-coatings. Part 2

The values of residual stresses in PVD-coatings of titanium, aluminum and niobium nitrides are determined by the flexible specimen method. An experimental-and-calculation procedure for separating the structural and thermal components of residual stresses is proposed that allows one to determine the thermal expansion coefficients of the coating materials and a general level of residual stresses in coatings on a substrate of any material. The dependence of the residual stress on the roughness of the substrate surface is established. The possibility of adjusting the level of residual stresses in coatings by the discrete surface topography formation is shown.     

等离子熔覆ZrB_2-ZrC/Fe复合涂层组织及耐磨性

采用等离子熔覆技术,以Zr、Fe、B_4C混合粉末为原料,在Q235低碳钢表面原位反应合成了ZrB_2和ZrC增强的Fe基复合涂层,分析了ZrB_2-ZrC/Fe涂层的物相组成和组织结构,并进行了硬度、耐磨性对比试验,探讨了物相和组织结构的形成过程及磨损机制。结果表明:涂层主要物相为ZrB_2、α-Fe、ZrC、Fe_2B和Fe_3C,其中ZrB_2呈现针棒状、花瓣状,ZrC呈现规则的颗粒状;随着原始粉末中(Zr+B_4C)含量的增加,增强相ZrB_2和ZrC含量增多,尺寸变大,ZrB_2-ZrC/Fe涂层与Q235钢基体之间结合紧密,呈冶金结合;与Q235钢基体相比,ZrB_2-ZrC/Fe涂层耐磨性显著提高,最高可达基体的5.45倍,ZrB_2-ZrC/Fe涂层的磨损方式以磨粒磨损为主,断裂方式以穿晶断裂为主。     

A numerical study of contact damage and stress phenomena in curved porcelain/glass-filled polymer bilayers

Finite Element Analysis is used to examine contact damage induced by Hertzian indentation of a porcelain coating on a glass-filled polymeric substrate. Different forms of cracking in the porcelain coating are studied –“Hertzian” cone cracks close to the indenter, more distant “outer” cone cracks, and “radial” cracking at the coating/substrate interface. The effects of porcelain coating thickness and radius of curvature on the critical stresses for initiation of these cracks are examined. The predicted critical load curves suggest that for systems with compliant substrates (relative to the coating) with a given radius of curvature, there is an optimum porcelain coating thickness that maximises the critical load for cone cracking. Conversely, for a given coating thickness, the effects of curvature vary significantly – for thinner coatings, where outer cone cracks are dominant, highly convex surfaces are more resistant to cracking, whereas for thicker coatings, which are more prone to Hertzian cone cracking, concave surfaces produce a higher predicted critical load. Curvature is observed to have little effect on the critical load for the formation of radial cracks, which remains the dominant mode of failure in cases of thin coatings on compliant substrates.     

Virtuelles Werkstoff‐ und Prozessdesign funktionaler Schichten

Virtual Material‐ and Processdesign of Functional Coatings Thermally sprayed and plasma transferred arc clad coatings are often used to improve the surface properties of mechanical parts with regard to an improved wear and corrosion behavior. New coating processes and applications can be developed, if it is possible to control the coating microstructure by a defined management of the process parameters. Simulation can be used to get a detailed understanding of the process‐material interaction for a defined controlling of the process parameters with less experimental effort. This allows a systematic variation of the coating structure and to calculate the parameter set which represents the best compromise between a high deposition rate and low residual stresses in the coating. In order to model thermal spraying, the following sub‐processes are considered: gas flow, material supply, heating and accelerating of particles, particle impact on the substrate, coating formation, solidification and formation of residual stresses. The results presented in this paper will demonstrate the influence of the process parameters on particle properties and subsequently on the splat formation, the coating formation and the coating microstructure. Controlling different process parameters like material injection conditions and substrate properties, the heating, cooling and solidification behavior of the particles and the coating structure can be influenced significantly.     

A study towards improving mechanical properties of sol-gel coatings for polycarbonate

Scratch-resistant coatings based on 3-glycidoxypropyltrimethoxysilane and tetraethylorthosilicate with a cross-linking agent and different amounts of colloidal silica are prepared on polycarbonate substrates by sol-gel technique. The failure mode of this type of coating on soft plastic substrate under pencil scratch test is studied. It is found that the pencil scratch failure contains a gouge failure under the static pressure and a film cracking failure under the sliding of the pencil tip. The gouge failure is due to the early plastic deformation in the substrate, while the film cracking is due to the tensile stress in the film induced by the sliding and friction of the pencil tip. Factors influencing the static gouge failure and sliding cracking failure are investigated. It is found that the cross-linking agent and colloidal silica filler increase the intrinsic cross-linking, hardness, elastic modulus and fracture toughness of the coating material, therefore, reduce the film cracking tendency; whereas the increased layer thickness and multi-layer coating improve the pencil scratch resistance significantly via delayed plastic deformation in the substrate. Based on these analyses, we conclude that the main factors towards improved pencil scratch resistance are: layer thickness, elastic modulus, fracture toughness and intrinsic hardness of the coating material. Pencil hardness is increased from grade 2B to 5H by adjusting these parameters.     

用涂层压入仪测定薄膜与基体结合强度的探讨

用新颖的能连续加载、卸载并配有声发射监测的涂层压入仪 ,对薄膜与基体的结合强度进行了探讨。实验结果表明 ,膜或膜 /基破坏的声发射信号各有特点 ,可区分压入过程中 (含卸载 )开裂和剥落及其对应的载荷值。压入法的临界载荷 pc 为加载过程中使膜发生初始剥落的外载 ,用涂层压入仪可精确测定。 pc 值对基体硬度和表面粗糙度的变化敏感。故用涂层压入仪可以实现用压入法考察膜 /基结合强度     

The application of X-ray photoelectron spectroscopy to the study of polymer-to-metal adhesion

The cathodic disbondment of a fusion-bonded epoxy coating applied to mild steel treated with a phosphoric acid wash has been investigated. The interfacial chemistry of disbondment has been studied by X-ray photoelectron spectrscopy (XPS), which shows the locus of failure to alternate between cohesive failure of the polymer coating and a phosphate-bearing layer. The kinetics of delamination are substantially reduced compared with data obtained for epoxy applied to a bare steel substrate. It is concluded that the application of an acid wash treatment results in a stronger, more durable, polymer-to-substrate bond. The process parameters of the wash treatment control both the substrate surface chemistry prior to coating and the eventual failure mode.     

Optical forces in hybrid plasmonic waveguides

We demonstrate that in a hybrid plasmonic system the optical force exerted on a dielectric waveguide by a metallic substrate is enhanced by more than 1 order of magnitude compared to the force between a photonic waveguide and a dielectric substrate. A nanoscale gap between the dielectric waveguide and the metallic substrate leads to deep subwavelength optical energy confinement with ultralow mode propagation loss and hence results in the enhanced optical forces at low input optical power, as numerically demonstrated by both Maxwell's stress tensor formalism and the coupled mode theory analysis. Moreover, the hybridization between the surface plasmon modes and waveguide modes allows efficient optical trapping of single dielectric nanoparticle with size of only several nanometers in the gap region, manifesting various optomechanical applications such as nanoscale optical tweezers.     

NdFeB磁性基材化学镀Ni-Cu-P初期形核过程及机赦

为了弄清NdFeB磁性材料表面化学镀Ni-Cu-P合金初期形核过程及机制,研究了不同时间化学镀Ni-Cu-P合金层初期形核过程、形貌和组织结构特征。结果表明：初期沉积过程具有明显的择优倾向和不均匀性：Ni和Cu原子并非以单个原子的形式沉积于基体表面,而是还原后在固．液界面处形成原子团在基体表面高能量区域优先沉积形核,然...     

Development of coating by thermal plasma spraying under very low-pressure condition <1 mbar

Very Low-Pressure Plasma Spray (VLPPS under 1 mbar) has been developed and used for deposition of copper powder (10-63 μm) coating on stainless steel substrate. In order to improve the understanding of this technique and to study the volatilization of the injected powder in supersonic plasma, optical emission spectroscopy study has been carried out. Preliminary results of the properties and the structure of VLPPS copper coating are presented. It is shown that the plasma expansion with decreasing chamber pressure increases the volatilization of particles and allows to obtain a very dense coating with crystalline structures and avoids oxygen, due to the preheating of the substrate with plasma (length about 1.50 m).     

Tribological characteristics of boronized niobium for biojoint applications

Boride coatings on corrosion-resistant refractory metals are potentially used as implanting materials. In this research, we investigated wear mechanisms of boride coatings on pure niobium using a pin-on-disk tribometer in two different conditions i.e. in dry and using a simulated body fluid (SBF). Surface morphology studied using a scanning electron microscope (SEM) shows the compressed boride layer with indistinguishable regions such as coating intermediate transition layer and the substrate. The surface analysis after wear tests was conducted using an atomic force microscope (AFM). It was found that, in dry condition, the boride coating underwent deformation wear, and debris formed and accumulated at both ends of the track due to adhesion. In presence of SBF, the coating shows different mode of failure. The tribo-chemical wear dominates the wear mode.     

电磁轨道失效与表面喷涂Mo技术研究

为提高电磁轨道材料性能,采用等离子喷涂技术在45CrNiMoVA钢表面制备了Mo涂层,观察了涂层显微形貌,测试了显微硬度和载流摩擦磨损性能,并与基体进行了比较。结果表明:Mo涂层显微硬度平均值为482.3HV1 N,比基体45CrNiMoVA钢硬度提高1倍。涂层与基体结合强度为41.5 MPa,结合方式为机械结合;同等载流摩擦磨损试验条件下,与基体45CrNiMoVA钢相比,Mo涂层磨合时间较短,摩擦系数更小(0.6),耐电弧烧蚀能力强,磨损量小;涂层磨损机理为断续式黏着磨损。