Microgrinding of Nanostructured Material Coatings

This study is aimed at experimentally investigating the effect of microgrinding process on the surface finish, subsurface damage and residual stresses of thermally sprayed nanostructured WC/12Co (n-WC/12Co) and Al₂O₃/13TiO₂ (n-Al₂O₃/13TiO₂) coatings. The material removal mechanisms are discussed. Surface textures are measured with stylus profilometry, scanning electronic microscopy (SEM) and atomic force microscopy (AFM), and analyzed using conventional methods and scale-sensitive fractal analysis. Residual stresses are measured with glancing incident X-ray diffraction (GIXD) technique that is capable of providing the depth profiles of residual stresses. Investigated is also grinding damage to the coatings.     

Grinding of nanostructural ceramic coatings: damage evaluation

This paper investigates the damage, mainly surface and subsurface cracks, in ground n-Al₂O₃/13TiO₂ and n-WC/12Co coatings. Surface cracks are formed under some special conditions. The presence and formation of the surface cracks are studied.Subsurface damage, especially cracks, of the ground components greatly influences their performance and life in service. The effects of the grinding conditions such as material removal rate, wheel grit size and bond materials on the subsurface damage, especially subsurface cracks, are investigated. The difference of material properties of these two coatings also influences the subsurface cracks. Different from bulk samples, large quantities of defects inherited from the thermal spray process play a significant role in the initiation and development of the cracks, present the crack configurations more complex than the typically reported system of median and lateral cracks observed in ground bulk ceramics. This complexity is analyzed.     

Microstructures of nanostructured ceramic coatings obtained by suspension thermal spraying

In the present work, the elaboration of nanostructured alumina and titania coatings by thermal spraying with liquid precursors is described. Nano- and submicrometer-sized powders were used to prepare aqueous or alcoholic suspensions. The suspensions were sprayed using APS and HVOF processes in order to obtain thin and thick deposits. The paper discusses the coating microstructures as a function of suspension characteristics and spray parameters in both APS and HVOF processes.     

超音速火焰喷涂纳米结构涂层研究进展

超音速火焰(High Velocity Oxy -Fuel,简称HVOF)喷涂具有高速和相对较低的温度两个重要特征,能够获得比普通火焰喷涂或等离子喷涂(Plasma Spray,简称PS)结合强度更高的致密涂层.纳米材料具有独特的表面效应、体积效应及量子尺寸效应,其电学、力学、磁学、光学和热学等性能产生了惊人的变化.随着材料科学技术的深入发展, 在实际生产和生活中运用性能优良的纳米材料倍受人们关注,其中,采用热喷涂技术制备纳米结构涂层是构筑纳米结构材料的最具前途的方法之一.从目前国内外的情况来看,HVOF喷涂纳米结构涂层技术的研究取得了较大的进展.综合国内外文献,总结了HVOF喷涂制备纳米结构涂层的研究现状,着重阐述了热喷涂纳米涂层的基本过程和结合机理,指出了利用HVOF喷涂纳米结构涂层存在的问题,并对热喷涂纳米结构涂层的发展前景作了展望.     

HVOF喷涂纳米结构WC-12Co涂层的组织结构分析

纳米结构WC-12Co涂层的研究目前已受到了广泛重视,对其组织结构及影响因素的研究有利于提高涂层性能.采用HVOF工艺制备了纳米结构、多峰结构及普通微米结构3种WC-12Co金属陶瓷复合涂层,并采用SEM、XRD等对粉末及涂层的显微形貌、组织结构进行了分析;探讨了粉末在喷涂过程中的氧化脱碳机理,并指出了与之相关的影响因素.结果表明:纳米结构WC-12Co涂层结构致密,孔隙率低,与基体结合状态良好;纳米粉末在喷涂过程中比微米粉末氧化失碳严重,并发生了不同的纳米晶粒的长大;纳米粉末在喷涂过程中的氧化脱碳程度不仅与喷涂工艺有关,还在很大程度上取决于粉末本身的结构特性.     

纳米材料的马氏体相变

简述了纳米材料的定义、制备、结构、性能和应用。总结了马氏体相变的尺寸效应。概括了近十年来,纳米材料的马氏体相变和热力学研究的最新结果。     

Effect of tribological media on tribological properties of multilayer Cr(N)/C(DLC) coatings

In this research, Cr(N)/C(DLC) multilayered coatings were deposited on M2 steel substrates by an unbalanced magnetron sputtering technique. By varying the substrate rotation speed, four multilayered coatings with different bilayer thickness were produced. The bilayer thickness and structure of multilayered coatings were characterized by low-angle XRD, XPS depth profile, and cross-section TEM observation. The tribological investigation focused on the effect of layer thickness and tribological media on tribological property of the multilayer coatings against Al counterface. A pin-on-disc tribometer with a tribological medium container was used to investigate the wear behaviours of the four multilayered coatings under dry and wet (distilled water and S500 coolant) sliding. A stylus surface profilometer was used to measure wear rate. The investigation of wear tracks and wear mechanism was performed using Scanning Electron Microscopy (SEM). The research results showed that coatings with different bilayer period performed different tribological behaviour. The proper tribological media applied in the wear tests could improve the wear properties of multilayer coatings.     

AC-HVAF喷涂高铬镍基合金纳米结构涂层的热腐蚀性能研究

使用AC-HVAF喷涂工艺分别制备了纳米和微米结构的高铬镍基合金涂层,对两种涂层和20G钢在550℃和650℃表面涂盐情况下的热腐蚀性能进行了研究,并利用配有能谱分析仪的扫描电镜(SEM)和X-ray衍射仪(XRD)对涂层腐蚀产物的形貌、成分和相组成进行了分析.试验结果表明,腐蚀后的两种涂层表面均生成一层连续致密的氧化铬保护膜,可有效抑制腐蚀反应的进程.在相同腐蚀条件下,纳米结构涂层比微米结构涂层具有更低的腐蚀增重,显示出更优异的抗热腐蚀性能.     

Study of oxidation behavior of nanostructured NiCrAlY bond coatings deposited by cold spraying

Nanostructured NiCrAlY bond coating was deposited using a milled powder by cold spraying. A shot-peening treatment was then applied to the as-sprayed coating to modify the coating surface morphology. The oxidation behavior of the coating with the as-sprayed surface and shot-peened surface was investigated under isothermal oxidation at 900 °C and 1000 °C for different times. The oxidation behavior of the coating was characterized through surface morphology and cross-sectional microstructure by scanning electron microscopy. It was found that a uniform oxide layer was formed on the surface of the shot-peened nanostructured NiCrAlY coating during oxidation at temperatures of 900 °C and 1000 °C. The surface morphology of the coating has significant effect on the morphology of the oxide. The surface geometry of the cold-sprayed MCrAlY coating must be modified to promote formation of a protective oxide film during oxidation, through application of a post-treatment process such as shot-peening.     

Nanostructured coatings produced by a novel ultrasonic-assisted method: Coating characterisation and formation mechanism

In this study, we introduce a novel method of mechanical plating to produce nanopowder coatings on a number of metal substrates by using TiN nanopowder as a representative example. This method, proposed earlier by the authors, allows a coating to be applied at room temperatures and atmospheric pressure in a relatively short time. These coatings were characterised for microhardness, roughness, and scratch adhesion. Their micro- and nanostructures were investigated by SEM and TEM. On the basis of the results of these analyses, possible mechanisms of coating formation were tentatively proposed and discussed. To further elucidate the coating formation mechanisms and to estimate the process capability, a mathematical model was developed and verified against the experimental results.     

树脂基复合材料用陶瓷涂层防护性能分析

采用等离子喷涂铝粉作为打底材料在碳纤维增强聚酰亚胺复合材料（PMC）基体上制备了Al2O3和ZrO2轻质陶瓷防护涂层，测试了涂层的剪切结合强度、耐热循环性能、抗冲蚀性能、隔热性能。结果表明，等离子喷涂铝粉作打底层的涂层系统，性能优于电弧喷铝或电弧喷锌作打底层的涂层系统。带有Al2O3涂层的试样失重不到基体材料失重的1／3，Al2O3和ZrO2陶瓷涂层都可以为聚酰亚胺复合材料基体提供有效的冲蚀防护。Al2O3和ZrO2陶瓷涂层都可以为聚酰亚胺复合材料基体提供有效的隔热防护，ZrO2涂层隔热性能优于Al2O3涂层。     

玻璃鳞片树脂涂料的施工

分析了玻璃鳞片生产原理;玻璃鳞片在涂料中耐腐蚀作用;介绍了玻璃鳞片如何施工以及施工后的效果。     

Nanostructured coatings for machining and wear-resistant applications

Nanostructured coatings offer great potential for various applications due to their superior characteristics that are not typicallyfound in conventional coatings. In this paper, the development and synthesis techniques of nanostructured coatings for machining and wear-resistance applications are reviewed.     

Molecular simulation of interfacial reaction between TiAl alloy melts and different coatings

The effect of coatings (Y2O3, ZrO2 and Al2O3) on the interfacial reaction of TiAl alloys was studied with molecular dynamics. The binding energy of coatings and the diffusion process of oxygen in the melt were simulated, and then the simulation results were compared with the experimental results. The simulation results indicate that for each of the three simulated coatings, inordinate interfacial reactions have occurred between the coating and the melt. The binding energy results show that Y2O3 has the best stability and is the most difficult to break down. ZrO2 has the greatest decomposition energy and is the easiest to break down in the melt. Besides,the molecular dynamics indicate that the diffusion coefficient of the oxygen atom in Al2O3 is larger than that in the other two coatings, indicating that oxygen diffusion in Al2O3 is the fastest at a given temperature. The experimental results show that the oxygen concentration of the melt with Al2O3 coating is the highest, and the oxygen diffusion is of similar magnitude to the simulation values, from which the conclusion can be obtained that the oxygen concentration is significantly influenced by the coating materials.     

热喷涂NiCr/纳米(Zr02 +8% Y2 03)梯度涂层的性能研究

针对陶瓷涂层与基体结合强度低、易产生裂纹和剥落的现象,进行了抗高温氧化耐磨损梯度涂层的设计。采用热喷涂技术在45钢基体表面制备由面层[纳米（Zr02 +8% Y203）]和中间层(NiCr)组成的梯度涂层,利用扫描电镜(SEM)、测定结合强度、测定显微硬度、X射线衍射等方法研究涂层的性能。结果表明：NiCr/纳米(Zr02+ 8% Y203)梯度涂层显微组织结构致密,与NiCr合金涂层和纳米(Zr02,+8% Y2 03)陶瓷涂层相比,具有更优良的力学性能;梯度涂层的面层有利于提高基体的耐高温、耐磨损性能,而中间层则有利于改善基体的抗高温氧化性能。     

Biomimetic coating of calcium phosphate on materials

The biomimetic coating process in comparison with other processes is reviewed. This processing shows advantages in the surface bio-modification, such as low cost and flexible processing, wide range of apatite composition and thickness, non-line-of-sight characteristic and possibility to coat polymers and porous implants. The biomimetic apatite coating is made up of larger number of globules with size of 1 - 5μm. Each globule is a group of numerous flakes with a size range of 100 - 200 nm to 30 μm in length and 0. 1 - 1 μm in thickness. In-vitro and in-vivo studies show that the biomimetic apatite coating can promote an early and strong bonding to bone or promote the bone in-growth into the porous structure, which will be beneficial to the cementless stable fixation of orthopaedic implants. Recently developed co-precipitation of a kind of protein molecules into the HA coating shows much promising.     

金刚石颗粒强化银基复合镀层

在制备银基金刚石颗粒复合镀层的基础上 ,研究了复合镀层的力学性能和电接触性能 ,以及电镀工艺对镀层结构的影响。结果表明 ,金刚石粉末能够提高银镀层的硬度 ,降低其电磨损率 ,从而提高电触头的寿命及耐大电流的能力。金刚石粒径越小、浓度越高 (在一定的范围内 ) ,强化效果越好。影响复合镀层结构的因素有很多 ,各因素必须相互协调 ,才可得到与衬底结合牢固的、颗粒均匀分布的结晶致密的复合镀层。镀液中金刚石含量不很高时 ,其最优化工艺与常规镀银相仿 ,使用适量的分散剂并加以搅拌有利于金刚石粉末在镀层中的均匀分布。     

Nanostructured zirconia coatings processed by PROSOL deposition

The development of nanostructured coatings is a new field of interest in the world of thermal spraying. Novel techniques, such as HVOF or plasma spraying have been developed with respect to thermally activated processes, in order to reach the nanometric scale (10-20 nm). Frequently, the evolution consists in using agglomerated nanoparticles or suspension feedings. The CEA has patented a process called PROSOL [K. Wittmann-Ténèze, K. Vallé, L. Bianchi, F. Blein, P. Belleville, CEA Le Ripault, France, “Revêtement nanostructuré et procédé de revêtement”, Fr patent n°04 52390, (2004).], which is based on the injection of a sol-gel colloidal solution in a plasma source. Studies on the resulting coatings have principally shown that a nanostructured material could be prepared all the while preserving the intrinsic properties of the nanoparticle sol, the nanoparticle size and the crystalline phase distribution.The present investigation illustrates the PROSOL process through an example of spraying of a zirconia (ZrO₂) sol, prepared under hydrothermal conditions, in an atmospheric plasma jet. A time-stabilized sol of zirconia nanoparticles (10 nm) crystallized in both monoclinic and tetragonal phases was obtained. The injection of such a sol in the plasma plume was performed through a liquid injector that dispensed a sol jet under pressure without any pulverization gas. Because of the high temperature and the high velocity medium, the sol was fragmented into droplets and the liquid phase was vaporized. The resulting nanoparticle agglomerates embedded in droplets were accelerated and collected on a substrate without melting. By adjusting the plasma spraying parameters, more or less dense coatings could be obtained. Various characterization techniques were performed on the as-sprayed layers, including SEM, XRD and TEM. Results showed that the coatings were constituted of 10 nm-sized grains in the monoclinic and tetragonal phases. The flexibility of the process was also highlighted, i.e., the possibility to obtain coatings with thicknesses between one and several microns, produced without any physical change at a given deposition rate, on a variety of geometries and on a vast range of substrates.     

热喷涂纳米涂层与基体结合强度的研究

分别以微米与纳米NiC/WC粉末为原料,采用活性燃烧超音速火焰喷涂技术制备了金属陶瓷涂层。采用最新的结合强度标准较准确地测试了涂层的结合强度,利用SEM分析了拉伸断口的成分分布和微观形貌。研究表明,用活性燃烧超音速火焰喷涂技术制备的纳米复合涂层的结合强度为163MPa。     

Design and performance of AlTiN and TiAlCrN PVD coatings for machining of hard to cut materials

Machining of hard to cut materials such as hardened steels and high temperature strong aerospace materials is a challenge of modern manufacturing. Two categories of the aluminum-rich TiAlN-based Physical Vapor Deposited (PVD) coatings, namely AlTiN and TiAlCrN, are commonly used for this area of application. A comparative investigation of the structural characteristics, various micro-mechanical properties, oxidation resistance and service properties of the both coatings has been performed.Crystal structure has been studied using High Resolution Transmission Electron Microscopy (HR TEM). Electronic structure has been investigated using X-ray Photoelectron Spectroscopy (XPS). Micro-mechanical properties (microhardness, plasticity index, impact fatigue fracture resistance) have been evaluated using a Micro Materials Nano-Test System. Short-term oxidation resistance has been studied at 900 °C in air. The tool life of the coating was studied during ball nose end milling of hardened H 13 tool steel as well as end milling of aerospace alloys such as Ni-based superalloy (Waspalloy) and Ti alloy (TiAl₆V₄).It was shown that the set of characteristics that control wear performance strongly depend on specific applications. For machining of hardened tool steels, when heavy loads/high temperatures control wear behavior, the coating has to possess a well-known combination of high hot hardness and improved oxidation resistance at elevated temperatures. To achieve these properties, crystal structure for TiAlN-based coatings should be mainly B1, and elemental composition of the coating should ensure formation of strong inter-atomic bonds such as Al-Cr metal-covalent bonds in the TiAlCrN coating. Nano-crystalline structure with grain size of around 10-30 nm enhances necessary properties of the coating.In contrast, for machining of aerospace alloys, when elevated load/temperature combined with intensive adhesive interaction with workpiece material results in unstable attrition wear with deep surface damage, the coating should possess a different set of characteristics. Crystal structure for TiAlN-based coatings is basically B1; but due to a high amount of aluminum, the AlTiN coating contains AlN domains. The coating has a very fine-grained nano-crystalline structure (grains sized around 5 nm). Electron structure of energy levels indicates formation of metallic bonds. This results in plasticity increase at the cost of hot hardness reduction. The surface is able to dissipate energy by means of plastic deformation (instead of crack formation) and in this way, surface damage is reduced.