喷枪扫描速度对等离子喷涂Mo/8YSZ梯度 热障涂层温度场的影响规律研究

目的 突破新型动力热障涂层高温环境易剥落的技术瓶颈,揭示等离子喷涂过程中,喷枪扫描速度对梯度热障涂层温度分布的影响规律。方法 利用ANSYS有限元仿真模拟软件,建立了等离子喷涂Mo/8YSZ梯度热障涂层温度场的仿真模型,模型中考虑了材料热物性参数随温度的变化情况及材料的相变潜热。 结果 当喷枪扫描速度由550 mm/s增加至1000 mm/s时,喷枪与基体或已沉积涂层间交互作用的时间缩短,在喷涂构件自身热传导及喷涂构件与外界环境对流换热等综合因素作用下,致使喷涂作业结束时,喷涂构件的最高温度由475 ℃降低至371 ℃,涂层厚度方向的最大温度梯度由2.15×107 ℃/m降低至2.05×107 ℃/m。由于喷涂构件的温度、温度梯度及等离子射流热源用于粉末粒子直接温升的比例均与材料的热物性参数密切相关,致使在喷涂作业结束时,喷涂构件各部分最高温度及涂层厚度方向的最大温度梯度均呈现陶瓷层最高、过渡层次之、粘结层最低的分布规律。由于等离子喷涂过程中,先沉积的涂层对后沉积的涂层存在一个预热作用,故伴随着涂层厚度的增加,喷涂构件的最高温度增加。结论 在等离子喷涂过程中,通过增大喷枪扫描速度,可在牺牲涂层最高温度的条件下,降低喷涂构件的最大温度梯度。热障涂层采用梯度结构,可实现涂层厚度方向材料热物性参数的连续梯度变化,进而实现对喷涂构件空间温度分布的有效调控。     

等离子喷涂陶瓷涂层基体温度变化对结合强度和残余应力的影响

喷涂产生的残余应力对涂层结合强度的影响极大,而残余应力是由喷涂过程中基体温度的急剧变化以及基体和陶瓷涂层的热膨胀系数存在明显差异造成的,又与喷涂时温度脉动产生的沿涂层深度方向较大的温度梯度密切相关。残余应力的精确测定一直未得到解决。本文系用最新研制的测试仪可完成对残余应力的精确测定。即当等离子喷枪在喷涂过程中沿着试件表面某个方向往复移动时,用接触式高精度位移传感器测试基体背面由于加热、骤冷引起的梯度变化,在此同时用固定在基体上的热电偶测量基体的温度变化,再通过应力应变关系计算得到残余应力,结合对喷涂后结合强度的测试,就可得到涂层形成过程中基体的温度变化对结合强度和残余应力的影响规律。     

等离子熔-喷WC-17%Co涂层工艺参数对外观形貌的影响

等离子熔-喷技术同时具备等离子喷涂、熔焊技术的综合特点,可以实现各种陶瓷材料涂层与基体的冶金结合。Co基WC具有硬度高、耐磨损、耐腐蚀、耐高温等一系列优点。采用等离子熔-喷技术在Q235钢基体表面制备WC-17％Co涂层,通过研究等离子熔-喷工艺参数（等离子熔枪和喷枪角度、熔枪和喷枪与基材表面的距离、熔-喷速度、喷涂送粉量）对涂层外观形貌的影响,获得最佳的工艺参数,制备出外观形貌良好、无缺陷的熔-喷涂层。     

铝基非晶纳米晶复合涂层的喷涂工艺

为了研究喷涂参数对涂层性能的影响规律,采用高速电弧喷涂技术制备铝基非晶纳米晶复合涂层,利用正交试验法系统研究喷涂电流、喷涂电压、喷涂距离、喷枪移动速度和雾化空气压力对涂层性能的影响规律。优化后的工艺参数为喷涂电流160 A,喷涂电压36 V,喷涂距离200 mm,喷枪移动速度300 mm/s,雾化空气压力0.7 MPa,喷涂参数对涂层性能影响的主次顺序为：雾化空气压力、喷涂电压、喷枪移动速度、喷涂电流和喷涂距离。采用扫描电子显微镜(SEM)、能谱仪（EDS）、X射线衍射仪（XRD）和透射电镜（TEM）对工艺优化后的涂层进行分析,同时对涂层的显微硬度和孔隙率进行了测试。结果表明,采用优化参数制备的涂层组织结构致密,孔隙率为1.13%,硬度可达392 HV0.1,涂层具有明显的非晶纳米晶相,非晶含量约为24.2%。     

大气物理气相沉积行为对层流等离子喷涂Mo涂层结构影响*

通过提高基体温度或粒子温度可以突破大气等离子喷涂涂层结合率一般不超过 1 / 3 的瓶颈，然而目前粒子温度难以通过提高功率等方式进一步提高。基于大气层流等离子喷涂的相关研究证明了层流等离子射流具有射流长度长、速度低、能量密度高等特点，能够有效通过提高粒子在等离子射流的滞留时间从而实现对粒子的充分加热。为了研究层流等离子喷涂高熔点 Mo 涂层的结构演变规律与关键影响因素，并推导出金属与陶瓷涂层的一般沉积行为，使用扫描电子显微镜对三种喷涂参数下制备的 Mo 涂层的结构进行了表征与分析。结果表明，喷涂过程中，在等离子射流以及高温粒子对基体的原位加热作用下，Mo 的氧化物蒸气能够在等离子射流扫掠中与扫掠后附着、沉积在涂层表面，从而影响后续 Mo 粒子的沉积而改变涂层的微观结构。涂层的结构主要与 Mo 粒子的蒸发和基体温度有关。粒子蒸发越剧烈，基体温度越高，涂层越趋向于呈现出多孔岛状凸起结构；粒子蒸发越弱，涂层越趋向于呈现出层状结构，有利于实现低氧化、高致密金属涂层的制备，拓宽等离子喷涂的应用。综合以上研究结果，揭示层流等离子射流中的粒子大量蒸发现象与气相沉积过程，为其作为一种大气环境物理气相沉积的实施方式奠定了基础。     

AZ31镁基体等离子喷涂NiAl粒子扁平行为研究

以抛光和喷砂的AZ31镁合金为基体,并在基体温度分别为25℃、150℃、250℃下,用等离子喷枪在基体表面喷涂NiAl粉末,研究熔滴粒子扁平行为及涂层的结合机理.研究结果表明:随着基体预热温度的升高,粒子中心扁平凝固区域逐渐扩大;NiAl粉末喷涂时很容易熔化镁合金基体表面,并使基体表面产生凹坑变形,主要是微区冶金结合,提高结合强度.     

激光等离子复合热源喷涂工艺沉积机理研究

目的提高涂层的结合强度和改善微观组织结构。方法选取WC-10Co4Cr喷涂材料,分别通过激光等离子复合热源喷涂工艺以及等离子喷涂工艺制备涂层,对涂层组织与基本性能进行检测,对两种不同喷涂工艺的沉积机理作对比分析研究。研究复合热源喷涂涂层微观组织结构以及涂层与基体间结合方式较等离子喷涂涂层的变化。利用高速摄像仪对激光等离子复合热源喷涂以及等离子喷涂的工艺过程进行跟踪监测和分析,研究复合热源沉积过程中,基体表面微熔池的形成及粉末粒子在不同沉积工艺过程中熔融状态的对比,分析等离子喷涂涂层和复合热源喷涂涂层的沉积机理。结果等离子喷涂WC-10Co4Cr涂层以机械结合方式为主,涂层结合强度为39.5 MPa,孔隙率为1.7%,而激光等离子复合热源喷涂WC-10Co4Cr涂层实现了冶金结合,其结合强度提升到91 MPa,孔隙率降低到0.86%。结论激光等离子复合热源喷涂工艺可以有效提升涂层的结合力,改善涂层组织致密性,更有利于涂层的耐磨耐腐蚀性能。     

激光熔覆多层涂层温度场的数值模拟

基于ANSYS生死单元技术,建立了多层激光熔覆三维有限元分析模型,获得多层激光熔覆温度场的分布规律,同时分析预热温度对激光熔覆热循环的影响.试验结果表明,平行于热源移动方向的节点加热速度较快,降温速度缓慢;垂直于热源移动方向的节点,距离熔覆层中心越近,加热速度和冷却速度越大.y方向的结合处节点的温度梯度大于x方向的结合处节点的温度梯度;热输入保持不变时,随着预热温度的升高,加热速度变化较小,峰值温度升高,相变温度以上停留时间变长,但高温停留时间变化不大.预热温度为200?℃时,t8/5约为未预热下的3.2倍,预热可以减小熔覆层开裂倾向,有效降低涂层应力.     

超高强钢表面激光和等离子制备钕和镍基复合涂层界面的控形模拟研究

针对激光重熔等离子喷涂制备的耐磨防腐涂层与超高强钢基体结合界面的形貌控制问题,建立了激光重熔等离子喷涂制备的钕基和镍基复合涂层的数值模型,模型中考虑了材料不同温度下的热物理性能参数、不同温度下的相变潜热及激光热源等因素的综合影响。结果表明:随着激光功率的增加,涂层与基体结合界面的熔池形貌由扁平状逐渐过渡到月牙形与扁平形的复合形貌,这是由于等离子喷涂制备的涂层与基体的熔点及热物理性能参数等因素存在差异;随着激光扫描速度的增加,涂层与基体结合界面处的扁平形熔池和月牙形熔池的宽度降低,最大温度梯度增加;激光重熔过程中喷涂构件厚度方向的等值线疏密程度不同,呈现出"减小-增大-减小"的变化趋势。     

基于ANSYS生死单元法的多层等离子喷涂体系仿真

根据等离子喷涂的特点,采用ANSYS有限元软件中的单元生死法,建立多层等离子喷涂涂层体系直接热力耦合有限元模型。对等离子喷涂Ni/WC涂层每一层的温度场和应力场进行了分析。结果表明:随着沉积层的增多,涂层温度升高,至喷涂最外层时温度最高,可能会造成涂层表面烧损;喷涂端面热量积累多,对减小残余应力不利;涂层与基体结合面多次反复经历迅速升温降温,容易造成应力集中。基体与涂层的结合界面是残余应力高度集中区,其残余应力值大于涂层外表面的值;残应余力的最大值是径向拉伸应力;较低的冷却速率和冷却系数可减少残余应力的分布。     

An Investigation on Temperature Distribution Within the Substrate and Nozzle Wall in Cold Spraying by Numerical and Experimental Methods

During cold spraying (CS), heat exchange between the hot driving gas and the solid bodies, e.g., spray nozzle and substrate, results in the temperature redistribution within the solid bodies. In this study, numerical and experimental investigations on the heating behavior of the substrate and nozzle wall were conducted to clarify the temperature distribution within the solid bodies in CS. The results show that after heating by the hot gas, the highest temperature presents at the center point of the substrate and decreases toward the substrate back surface and edge. With increasing standoff distance or decreasing inlet temperature, the substrate temperature decreases gradually, but the temperature gradient within the substrate changes little. The numerical results are consistent with the experimental measurements. Besides, it is also found that increasing the substrate size (diameter) can lead to the gradual increment in the substrate temperature. Moreover, the numerical study on the temperature distribution within the nozzle wall reveals that the highest temperature presents at the throat section of the nozzle and that the nozzle material significantly affects the temperature distribution within the nozzle wall.     

气体放电热源喷涂技术的数值模拟研究现状∗

热喷涂技术是表面工程领域中极为重要的一种装备强化修复技术，其中以气体放电形式为热源的喷涂技术包括等离子喷涂和电弧喷涂，两者更是占据热喷涂领域的绝大市场份额，采用数值模拟可以解决一些在试验上较为棘手的重点研究问题， 如等离子体流场和熔滴传热传质行为等，以期实现工艺参数的准确调控和优异涂层的制备。研究电弧及等离子喷涂模拟的模型差异化问题及流场速度、温度、电磁性质，归纳相关模拟的发展历程，并调查试验与模拟的吻合程度。结果表明：电弧喷涂中丝材原料会使阴阳极产生温度差，水平速度分布较发散，熔滴模型也多未考虑熔滴群间相互作用；等离子喷涂研究中常用的三维瞬态双温模型已十分贴近实际工况，对熔滴飞行中的加热、加速过程及破碎行为的研究已较为完备，但仍存在湍流模型计算精度不够、对鞘层弧柱区的研究不够深入等问题。后续应重点在电弧喷涂多液滴模型、等离子体电磁作用和等离子丝材喷涂工艺的数值模拟等方面进行深入研究。     

The effect of heat treatment on the stiffness of zirconia top coats in plasma-sprayed TBCs

Thermal barrier coating (TBC) specimens have been prepared by plasma spraying. A vacuum plasma spray (VPS) MCrAlY bond coat and atmospheric plasma spray (APS) zirconia top coat were deposited onto a nickel superalloy substrate. The stiffness of detached top coats was measured by cantilever bending and also by nanoindentation procedures. Measurements were made on specimens in the as-sprayed state and after various heat treatments. Significant changes were detected in the Young's modulus of the top coat as a result of the heat treatments. The rate of sintering was found to be a function not only of the temperature but also of whether or not the coating was attached to the substrate during the heat treatment. This influences the stress state in the coating. A previously-developed numerical model has been modified in order to incorporate the effects of top-coat stiffening on the development of stress within the TBC system during exposure to high temperature. It is expected that sintering of the top coat will lead to increases in the driving force for debonding at the interface between the top coat and the bond coat. This effect may be at least partly responsible for the spallation of top coats which commonly afflicts TBCs after periods under service conditions.     

A novel integrated temperature investigation approach of sprayed coatings during APS process

Coating temperature is important for the coating reliability and reproducibility during the process of atmospheric plasma spray. A novel measurement and control approach for substrate and coating temperatures is presented. It is based on infrared (IR) pyrometry combined to specific robot spray trajectories in order to avoid harsh environment of spray workshops. The temperature evolution is continuously detected and recorded during preheating, spraying and cooling stages. The two specific factors, periodic average temperature and standard deviation were adopted to evaluate the temperature variation and the fluctuation of the thermal cycle relevant to one robot spray cycle based on the statistical method. These two factors are successful in describing the temperature variation during experimental processing sets. Finally, based on the monitoring system, the influence of Z-type robot spray trajectory parameters, including spray distance, scanning velocity and scanning step on coating temperature characterized by the two factors, is systemically investigated. Experimental results show that average temperature has no evident difference as a function of scanning velocity and no fixed relationship with scanning step, but just is dominated by the heating time of plasma jet and particle flux. Therefore, the selection of optimal scanning velocity just needs to take the temperature fluctuation into consideration. The temperature fluctuation decreases when scanning step increases, but both average temperature and fluctuation decrease with the increasing of spray distance and vice versa. Finally, on the basis of experimental results, a control experiment of sprayed coating temperature is presented to obtain constant temperature cycles by means of adjusting robot trajectories, cooling, among other considered operating parameters. Excellent control performance is observed.     

多功能超音速火焰喷涂粒子特性的数值模拟

通过建立多功能超音速火焰喷涂火焰流场的数值模型,对超音速火焰喷涂粒子的速度特性和温度特性进行数值模拟,其结果揭示了多功能超音速火焰喷涂粒子的速度和温度的变化规律.根据数值模拟结果分析了粉末粒度对火焰焰流速度和温度的影响,用不同粒度参数重复模拟计算,这对喷涂粉末的加速和加热性能具有重要意义.     

Comparison of plasma-sprayed coatings produced in argon or nitrogen atmosphere

When spraying is conducted at ambient atmosphere, the entrainment of air cools the plasma jet and affects its expansion. It can also cause oxidation or chemical decomposition of the sprayed materials. Inert plasma spraying (IPS), generally conducted in an argon atmosphere, prevents these phenomena. However, the main drawbacks of IPS in comparison with air plasma spraying are the capital and operating costs. This paper presents a study in which nitrogen is used as a substitute for conventional argon atmosphere, thus reducing costs by 25 to 30%. Titanium carbide and niobium powders were sprayed in both argon and nitrogen atmospheres. Cryogenic cooling of the substrate was used during the spray process. This helps to maintain a low temperature in the chamber, produce thick coatings, and allows the use of substrate materials that are sensitive to heat. The velocity, temperature, and composition fields of the argon-hydrogen plasma jet flowing in argon or nitrogen at atmospheric pressure are compared from numerical simulation. The adhesion, roughness, and microstructure of the niobium and TiC coatings produced in both atmospheres are discussed as well as their nitrogen content.     

Simulation of PYSZ particle impact and solidification in atmospheric plasma spraying coating process

In this work a numerical model of the impact and solidification of partially yttria stabilized zirconia particles on flat and rough substrate surfaces under plasma spraying conditions and the simulation results are presented. Results of the numerical simulation showed the influence of particle diameter and particle state prior to impact on splats spreading behavior and final morphology. The particles have a diameter range from 20 µm to 60 µm. Particle initial conditions prior to impact: speed, temperature and melting state are taken from previous simulation approaches of particle acceleration and heating. Simulations of fluid dynamics, heat transfer and solidification during the particle impact were performed using computational fluid dynamics. Tracing of free surfaces was determined by the volume of fluid method. The simulation results are compared with several numerical and experimental studies of other scientists and showed good agreement. Simulated splat morphologies are compared with experimentally obtained splats. The numerical model shows good results under real coating conditions and is suitable for the implementation in industrial applications. This model builds a basis for calculation of microstructure during real coating processes and can be used not only for coating under atmospheric plasma spraying conditions but also for similar coating processes and diverse materials.     

镀膜机雾化喷枪喷涂流场特性分析研究

空气雾化喷涂技术在手机屏幕的防水防油防指纹涂层、防爆涂层喷涂等工艺上有着极为重要的作用。为了提高手机玻璃屏幕防水涂层的喷涂稳定性和涂层均匀性,对空气雾化喷枪的喷涂流场特性进行仿真分析与研究。对某公司一款纳米镀膜机的KA-2自动喷枪进行拆解,根据测量的数据和喷枪实物的零件形状,建立喷枪的三维模型。在Fluent软件中建立雾化流场的双相流物理模型,使用VOF-DPM模型分析气相和液相在流场中的相互作用,对雾化压力和扇面控制压力做出改变,研究在不同参数下喷涂流场中气流速度的变化和流场分布,进行CFD流场仿真分析。最后得出当扇面控制气压在0.02~0.04 MPa、雾化气压在0.1~0.15 MPa时,喷涂图案效果最佳的结论。     

静电喷涂涂层厚度分布模型的研究进展

静电喷涂是利用高压静电电场使带负电的涂料微粒沿着电场相反的方向定向运动,并将涂料微粒吸附在工件表面的一种喷涂方法。在静电喷涂中,涂层厚度分布模型是喷涂机器人离线编程和轨迹规划作业中影响涂层厚度均匀性的关键因素,对提高喷涂质量和涂料转移率具有重要意义。因此,喷涂机器人轨迹规划的一个首要和基础的问题是如何建立准确的涂层厚度分布模型。重点综述了近年来静电喷涂涂层厚度分布模型的国内外研究进展,并在此基础上归纳了涂层厚度分布模型存在的问题,与此同时,归纳了常用涂层厚度仿真的方法—经验模型法和CFD仿真法。喷涂仿真包括静态喷涂仿真和动态喷涂仿真,静态仿真常用欧拉-欧拉法和欧拉-拉格朗日法,动态仿真常用动喷枪法和动壁面法,其中,动壁面法结合动网格为动态仿真主要方法。常见的动网格模型有三种:弹性光顺模型、铺层模型、局部重构模型。而在动态仿真中,动网格法常用有两种模型:一种是弹性光顺模型结合局部重构模型,另一种是铺层模型。最后对未来涂层厚度分布模型和涂层厚度仿真的研究进行了简要展望。     

大功率超音速等离子弧喷枪的研制

提出了大功率超音速等离子弧喷枪的设计原则和要求,经多次试验、改进,设计出双水内冷、双气路、双喷嘴的喷枪,其设计巧妙、结构合理、性能优良,满足了在大功率条件下对各种粉末材料的超音速喷涂。