涂层梯度液相烧结的原理和显微组织

讨论了均匀粉末压坯烧结时因热传而产生的温度分布存在的时间和空间上的异步现象,阐明了涂层烧结时梯度设计的必要性。分析了喷涂层梯度液相烧结的基本条件,并观察了其显微组织及其结合性能,结果表明,采用梯度设计可实现涂层稳定成形所需的液相烧结,避免了常规液相烧结时涂层的粘弹性流动。显微组织中氧化物有球化趋势,表导存在明显固-液相分界线,基材界面出现了冶金结合。     

Study of plasma- and detonation gun-sprayed alumina coatings using taguchi experimental design

Atmospheric plasma spraying (APS) is a most versatile thermal spray method for depositing alumina (Al₂O₃) coatings, and detonation gun (D-gun) spraying is an alternative thermal spray technology for depositing such coatings with extremely good wear characteristics. The present study is aimed at comparing the characteristics of Al₂O₃ coatings deposited using the above techniques by using Taguchi experimental design. Alumina coating experiments were conducted using a Taguchi fractional-factorial (L₈) design parametric study to optimize the spray process parameters for both APS and D-gun. The Taguchi design evaluated the effect of four APS and D-gun spray variables on the measured coating attributes. The coating qualities evaluated were surface roughness, porosity, microhardness, abrasion, and sliding wear. The results show that the coating quality is directly related to the corresponding coating microstructure, which is significantly influenced by the spray parameters employed. Though it is evident that the D-gun-sprayed coatings consistently exhibit dense and uniform microstructure, higher hardness, and superior tribological performance, the attainment of suitable plasma-sprayed coatings can be improved by employing the Taguchi analysis.     

Optimized multiaxis robot kinematic for HVOF spray coatings on complex shaped substrates

High accuracy robot systems are required for an efficient and reproducible application of thermal spray processes. Due to the influence of the torch trajectory on the heat and mass transfer processes during the deposition of APS and HVOF coatings, specific software tools for the simulation, generation and implementation of these trajectories must be developed. The internal HVOF series coating process of cylinder bores in lightweight engine manufacturing, the series production of optimized oxide ceramic coatings on textile surfaces and the trajectory generation and simulation for the coating of a complex 3D surface will be presented as case studies of these technologies.     

Development of superhydrophobic coating on paperboard surface using the Liquid Flame Spray

This paper introduces a new method for generating nanoscale coatings in a continuous roll-to-roll process at normal pressure. Nanostructured and transparent coating, based on titanium dioxide nanoparticles, was successfully deposited on-line at atmospheric conditions on pigment coated paperboard using a thermal spray method called the Liquid Flame Spray (LFS). The LFS coating process is described and the influences of process parameters on coating quality are discussed. Nanocoating was investigated by a field emission gun scanning electron microscope (FEG-SEM), an atomic force microscope (AFM), an X-ray photoelectron spectroscopy (XPS) and a water contact angle measurement.The highest measured water contact angles on the nanocoated paperboard surface were over 160°. Falling water droplets were able to bounce off the surface, which is illustrated by high speed video system images. Regardless of the high hydrophobicity, the coating showed sticky nature, creating a high adhesion to water droplets immediately as the motion of the droplets stopped. Nanocoating with full coverage of the substrate was produced at line speeds up to 150 m/min. Therefore, the LFS coating has scale up potential to industrial level as an affordable and efficient method for coating large volumes at high line speeds.     

Design of a fuzzy logic approach based on genetic algorithms for robust plasma-sprayed zirconia depositions

This paper proposes a design for an adaptive system by modeling the relationship between coating surface roughnesses and the controling factors in plasma spray coating processes. A statistical design was used to obtain sufficient experimental information with the least number of experiments. Analysis of variance was then used to select significant control factors for reinforced coatings, and these identified factors used to construct an adaptive fuzzy logic control model. In order to model the process, a fuzzy logic controller (FLC) was utilized. A genetic algorithm (GA) was applied as a tool to optimize rule bases from traditional FLCs. Therefore, with the use of a GA-optimized FLC, robust reinforced deposition for coatings in the plasma spraying process can be obtained. The experimental results show that the obtained optimal rule base for FLC is capable of achieving the desired results. That is to say, the proposed design, which combines a statistical method and a GA-optimized FLC, is efficient and robust for the investigation of reinforced coatings in a plasma spraying process.     

Zn-Al-Mg-RE涂层自封闭特性在复合涂层中的作用机制

通过铜加速醋酸盐雾腐蚀试验,研究了自封闭特性在Zn-Al-Mg-RE高速电弧喷涂层与舰船涂料结合成防腐复合涂层中的作用.经过480h的试验,在基体上直接涂装涂料的试样表面的划痕里充满了铁锈,而中间喷有高速电弧喷涂层的试样表面划痕里只有少量的白锈.这说明在腐蚀环境中,Zn-Al-Mg-RE高速电弧喷涂层表面的微观孔隙能够被自身的腐蚀产物堵塞,生成的腐蚀产物非常致密,能够阻止缺陷处继续被腐蚀.从试验结果可知在复合涂层体系中,高速电弧喷涂层的自封闭特性起到了积极的作用.     

Surface roughness of thermal spray coatings made with off-normal spray angles

The formation of a thermal spray coating using an off-normal direction angle for the spray has been analyzed to identify the causes of the large surface roughness of the coating. In the analysis, the string method was used for modeling the formation of the coating. The method uses a string of equally spaced node points to define the shape of the coating surface and to track the change in this shape as the thermal spray mass is deposited. The method allows for the calculation of arbitrary shapes for the coating surface that may be very complex. The model simulates the stochastic deposition of a large number of thermal spray droplets. Experiments were carried out to obtain the data used in the model for the mass flux distribution on the target surface. The data show that when the thermal spray mass impinges on the target surface a large fraction of it, called overspray, splashes off the target and is redeposited with a small direction angle. This component of the deposited mass results in a large coating roughness.     

面向自由曲面精准涂胶系统的设计与实现

大多数产品的外形都是不规则复杂曲面,智能涂胶设备要综合考虑胶接对象的多样性和复杂性。为了实现涂胶轨迹在各转角处保持尺寸一致,研制了面向自由曲面的精准涂胶系统,详细描述了系统的原理、软硬件及控制系统设计等。该系统通过工件模型建立准确涂胶轨迹,使用胶线质量模型计算胶线尺寸,使用超高速轮廓测量仪测量胶线尺寸并进行反馈微调。通过汽车扰流板涂胶试验,验证了该设备能满足曲面工件的精准涂胶要求。研究结果为涂胶机器人智能精准涂胶提供了科学依据、方法及创新技术。     

Optimization of a Rotating Twin Wire-Arc Spray Gun

This paper presents a CFD (Computational Fluid Dynamic) study and experimental results concerning a rotating twin wire-arc spray process for the production of coatings on engine cylinder bores. In this process, the wire atomization is performed using a gas injection coaxially with the cylinder axis. The thermal spray tool is equipped with a deviation head rotating around the cylinder axis and allowing deflecting the droplet spray perpendicularly to the cylinder surface. The initial deviation head was found to be not sufficiently efficient so that a new deviation head incorporating an inclined slot was designed and used. Both CFD results and experiments showed that this new deviation head is more efficient. Moreover, it allowed increasing the coating bond-strength up to the specifications imposed by PSA Peugeot-Citroen. The present article shows that the wire-arc spray technology may replace efficiently the Atmospheric Plasma Spray (APS) for the thermal spray of coatings on engine cylinder bores. Moreover, it shows how CFD may help in solving industrial problems. In particular, the FLUENT CFD code was used in order to perform improvements of the deviation head design. This article was originally published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, 2007.     

先进陶瓷涂层结构调控及其在固体氧化物燃料电池中的应用

等离子喷涂技术可以对陶瓷涂层的微观结构进行调控设计,因此在制备固体氧化物燃料电池方面具有独特的优势。基于等离子喷涂方法,可以直接制备或经过后处理获得致密的电解质涂层。采用等离子喷涂技术也可以制备高性能的多孔阳极和阴极,并可对钙钛矿结构阴极材料的成分和晶体结构进行调控。文中介绍了目前国内外采用涂层制备电池的方法,主要探讨了热喷涂方法制备电解质涂层的特点,对存在的问题和可行思路进行了讨论,并探讨了基于提高三相反应界面长度来制备高性能电极的方法。由于固体氧化物燃料全电池各功能层都有可能通过热喷涂方法制备,因此该方法在固体氧化物燃料电池结构设计具有巨大的潜力。     

喷涂层下基体疲劳裂纹的超声红外热成像检测

目的 验证一种喷涂层下基体疲劳裂纹红外热成像识别方法。方法 综合采用理论分析、数值模拟和试验研究相结合的方法,基于热波传导理论分析超声波激励下基体裂纹产生的热波与喷涂层裂纹产生的同频率热波,在向涂层表面传播过程中发生的叠加干涉效应,以及由此导致的表面热波相位偏移现象。采用数值模拟手段研究涂层裂纹热波与基体裂纹热波之间的叠加干涉规律,开展喷涂层下基体疲劳裂纹的超声红外热成像检测试验验证该方法的有效性。结果 受到脉冲超声波激励后,基体裂纹与涂层裂纹产生的热波向表面传导过程中会发生叠加干涉效应,并导致涂层表面热波相位发生偏移,低频热波相位偏移现象比高频热波更加明显。结论 采用涂层表面热波相位特征识别涂层下基体中的疲劳裂纹是一种可行且高效的方法。     

高速低温喷涂气固作用行为及喷涂系统研究进展

高速低温喷涂是利用固相或含固相的低温粉末在高速度、高动能作用下碰撞基体表面沉积的喷涂方法,具有氧化轻微、 结合牢固、组织致密、综合力学性能优异等潜在优势,在高性能金属或金属基复合材料涂层制备、增材制造和零件损伤修复等领域获得广泛关注。以粉末低温高速碰撞沉积过程为主线,凝练现有冷喷涂和低温超音速火焰喷涂两种具体工艺的共性特征,阐明喷涂气流与粉末颗粒的气固两相交互作用规律,分析出合理调控颗粒温度和速度是改善沉积体性能的关键。其次分析高速低温喷涂设备系统的构成,详细讨论各核心部件的结构设计策略及对气固流动行为的影响,总结出通过调整工艺参数与喷枪结构,可以实现颗粒温度和速度的按需控制。最后,对高速低温喷涂工艺及设备系统发展目前尚存的关键问题进行展望。总结如何通过喷涂参数与装置设计,最终达成调控沉积体性能的目的,有助于深入理解高速低温喷涂的沉积机理,对研制高性能的喷涂设备系统具有参考意义。     

On the use of auxiliary systems during thermal spraying

Whatever the degree of knowledge and control which can be obtained on each critical parameter of a thermal spray process, it seems now understood that it will ever be extremely difficult to obtain the desired properties of a coating only by controlling the spray parameters. In fact, a number of desired properties require contradictory settings of parameters, which rends necessary the choice of compromises. Therefore, it appears more and more necessary to introduce in the system new degrees of freedom in order to cut the Gordios' knot of the interrelated parameters.Those new degrees of freedom can be brought by auxiliary systems such as those enabling to control the surface state or the energy level in the system. Auxiliary systems could be defined in a number of ways, incorporating pre-treatments and post-treatments as well as control systems. In this paper, we shall only consider the systems, which are or could be implemented simultaneously to the deposition stage apart from the controlling devices. The purpose is to help and realise the usefulness of considering the possibility of using such devices in order to be able to design and produce more efficient thermal spray coatings.     

Post-treatment of thermal spray coatings on magnesium

Magnesium alloys have a beneficial combination of high strength to weight ratio, good machinability and high recycling potential. Despite this, the application of magnesium still is behind that of other constructive materials mainly due to low wear and corrosion resistance. For more demanding applications, a large amount of surface treatment methods are developed to overcome this problem. Thermal spraying is an efficient and flexible method of coating deposition and is widely used for protection of different materials against corrosion and wear. Nevertheless, the bonding of thermal spray coatings on magnesium alloys is not sufficient, so the following post-treatment processes are needed. One of such possibilities is high energy beam treatment of thermally sprayed coatings. During the heat treatment of magnesium substrates with coating the remelting of coating and a thin surface layer of substrate occurs. Depending on the combination of applied coating system and treatment method, different processes can be realised in modified layers: the alloying of magnesium substrate with other elements to improve corrosion properties, redistribution of hard particles from composite coating and new phases formation during the processing to improve the wear resistance of magnesium alloys. In the present work some examples concerning the laser and electron beam treatment of aluminium based composite coatings as well as infra red irradiation of zinc based coatings are described. Coatings are deposited on magnesium substrates (AM20, AZ31, AZ91) by arc spraying with Zn, ZnAl4 and ZnAl15 solid wires and cored wires in aluminium core with powder filling containing different hard particles, such as boron, silicon and tungsten carbide or titanium oxide. Remelting of thermal spray coatings is carried out by means of continuous irradiation of СО₂-laser in nitrogen or argon atmosphere, electron beam in vacuum and focused tungsten halogen lamp line heater in atmosphere. Microstructure of sprayed coatings as well as that of modified surface layers is investigated by metallographic methods. Corrosion properties are estimated by electrochemical measurements. Abrasion wear resistance of the modified layers is determined by scratch test, corundum grinding disk test and Rubber wheel test. It is shown that all methods applied for processing of thermal spray coatings lead to formation of modified surface layers in magnesium substrate with improved wear and corrosion properties. Different mechanisms of microstructure formation such as redistribution of chemical composition of composite coating components, partial remelting of hard phase particles, and new phases formation are discussed. Electrochemical behaviour of modified surface layers is mostly improved due to alloying, homogenization of element distribution and strong decrease of as-sprayed coating porosity. Abrasion wear resistance of processed magnesium substrates strongly depends on the microstructure and usually is 5 to 20 times higher compared with base material.     

HVOF Combustion spraying of inconel powder

A major trend in the thermal spray industry has been to increase the gas jet velocity to obtain better coating attributes. One emerging technology now used in industry is the high-velocity oxygen fuel process (HVOF). High-velocity spray guns combine oxygen and a fuel gas to generate heat and extremely high particle velocities. In this study, Inconel 718 powder was deposited on steel substrates. The primary coating function was electrical resistivity for a heater application. Experiments were conducted using a Taguchi L8 statistical fractional/factorial design parametric study. The Taguchi experiment evaluated the effect of six HVOF processing variables on the measured responses. The parameters were oxygen flow, fuel flow, air envelope gas flow, powder feed rate, spray distance, and nozzle configuration. The coatings were characterized by hardness tests, surface profilometry, optical metallography, and image analysis. This article investigates coating hardness, porosity, surface roughness, deposition efficiency, and microstructure with respect to the influence of the processing parameters. Analytical studies were conducted to investigate gas, particle, and coating dynamics for two of the HVOF thermal spray experiments.     

Studies on the thermal spraying of apatite bioceramics

Hydroxylapatite (HA) coatings on metal substrates have been investigated for many years. These coatings have proved to be compatible with bone. The degree of crystallinity of HA changed, and sometimes dissociation was observed with respect to the plasma spray process. However, the plasma spray process hardly altered the crystallographic structure, with only line broadening visible. Thein vitro solubility is dependent on the degree of crystallinity of the coating. Tensile strength measurements on the strength of the coating-substrate interface using various adhesives revealed a significant difference between epoxy resin and methacrylate. The failure mode of this tensile test was dependent on the coating thickness and surface texture (polished versus nonpolished). In animal studies, the fixation of hydroxylapatite plasma- spray coated cylinders as well as noncoated Ti- 6A1- 4V cylinders (Ti) in cortical bone was evaluated using pushout tests. It appeared that HA- coated implants showed higher push- out strengths in the first months than the titanium implants, because of the earlier bone formation against the HA coating.     

连铸结晶器铜板表面处理关键技术的研究与应用

结晶器涂镀前处理、表面涂镀层和涂层结构设计,是结晶器表面处理的关键技术.采用一步脱脂、刻蚀前处理工艺与采用传统前处理工艺相比,工件表面不仅粗糙度更高,而且更均匀.考察了几种结晶器表面涂镀层的热稳定性和耐磨损性能,喷涂涂层和Co-Ni镀层具有很好的热稳定性能和耐磨损性能,并具有良好的使用实绩.表面涂层的结构设计,包括涂层的厚度及厚度分布、多种涂层的组合使用等,都会显著影响结晶器的使用寿命.     

Trajectory Generation and Coupled Numerical Simulation for Thermal Spraying Applications on Complex Geometries

For high process reproducibility and optimized coating quality in thermal spray applications on complex geometries, atmospheric plasma spraying and high-velocity oxygen fuel torches are guided by advanced robot systems. The trajectory of the torch, the spray angle, and the relative speed between torch and component are crucial factors which affect the coating microstructure, properties, and, especially, the residual stress distribution. Thus, the requirement of high-performance thermally sprayed coatings with narrow dimensional tolerances leads to challenges in the field of robot-assisted handling, and software tools for efficient trajectory generation and robot programming are demanded. By appropriate data exchange, the automatically generated torch trajectory and speed profile can be integrated in finite element method models to analyze their influence on the heat and mass transfer during deposition. Coating experiments assisted by online diagnostics were performed to validate the developed software tools.     

热连轧冷却线工艺设计及软件开发

采用水力学模型和卷取温度数学模型分别研究了热连轧轧后冷却线设计中的水量计算和温度计算方法。基于集管上的鹅颈管管径、压力、位置分布等基础设备信息,进行了上下集管和侧喷管的流量计算、热流密度计算和冷却能力计算;基于冷却子区的上下喷射集管布置型式,进行了冷却线的集管数计算;基于产品大纲对冷却线的要求,进行了水量校核和温度模拟计算;基于冷却工艺、流量计算模块和温度计算模块,进行了冷却线工艺设计软件开发。多条冷却线参数的实际比对表明,所开发软件流量计算和温度计算准确,轧后冷却线设计信息可靠。