优化大气等离子喷涂工艺,降低TBC(热障涂层)生产成本.doc

TBC coating cost reduction by optimization of the Atmospheric Plasma Spray process 优化大气等离子喷涂工艺，降低TBC（热障涂层）生产成本S. Mihm, T. Duda, Birr / CH, G. Thomas, H. Gruner, Mgenwil / CH and B. Dzur, Ilmenau / DThe global economic growth has triggered a dramatic increase in the demand for resources over the last few years, resulting in steady price increases for energy and raw materials. In the gas turbine manufacturing sector, process optimizations of cost-intensive production steps involve a heightened savings potential and form the basis for securing future competitive advantages in the market economy.全球经济增长在过去的几年中引发了对资源需求急剧增加，导致能源和原材料价格稳步上涨。在燃气轮机制造业，对成本密集的生产工艺优化具有成本节约的潜力并能为企业在将来市场经济的竞争中打下坚实的基础。In this context, the atmospheric plasma spraying (APS) process for thermal barrier coatings (TBC) has been optimized. A constraint for the APS coating process optimization is the use of the existing coating equipment.在这样的大背景下，热障涂层（TBC）的大气等离子喷涂（APS）工艺得以改进优化。而APS制备涂层工艺优化的一个限制条件在于现有涂层设备的使用。Furthermore, the current coating quality and characteristics are not allowed to change in order to avoid new qualification and testing.此外，为了避免重新申请资质以及进行额外测试，还不能改变当前的涂层质量和性能。Using experience in atmospheric plasma spraying and empirically gained data, the process optimization plan included the variation of e.g. the plasma gas composition and flow rate, the electrical power, the arrangement and angle of the powder injectors to the plasma jet, the grain size distribution of the spray powder and the plasma torch movement procedure like spray distance, offset and iteration. In particular, plasma properties (enthalpy, velocity, temperature), powder injection conditions (injection point, injection speed, grain size distribution,) as well as the coating lamination (coating pattern, spraying distance) are examined. The optimized process and resulting coating was compared to the current situation by several diagnostics methods.在以往大气等离子喷涂经验和日常获取的宝贵数据基础上，我们的工艺优化计划包括一系列的改变，如等离子气体组成，流量；用电，布局及粉末注入等离子流的角度，粉末的粒径分布、等离子枪的移动（如喷距、偏差以及重复性等）。特别是等离子性能（焓值、速度以及温度），注粉条件（注粉点、注粉速度、粒径分布），以及还有涂层（涂层形式，喷涂距离）等方面做了重点研究。我们将优化后的工艺及其所制备的涂层与当前普遍使用的几种工艺采用不同的分析方法进行了对比。The improved process provides significantly lower costs by achieving the requirement of comparable coating quality. Furthermore, a contribution was made to a better comprehension of the atmospheric plasma spraying of ceramics and a method for future process developments was defined.在同等涂层质量的前提下，优化后的工艺能很大程度的降低生产成本。此外，我们对大气等离子陶瓷粉末喷涂过程做了一些详细描述，使其更加通俗易懂，同时，我们还了未来工艺的研发方法。1 Introduction 引言Plasma coated thermal barrier coatings (TBC) are successfully established in the gas turbine manufacturing business since the seventies 1. In the hot gas section of gas turbines TBCs fulfill the functions of thermal insulation, therefore lowering the temperature of the metallic portion of the part. Firing temperatures in the combustion chamber above 1300C and limited long term operation temperatures of approx. 950C for the metallic materials resulting in high requirements to coating systems on blades, vanes and combuster parts.从上世纪七十年代起，采用等离子技术制备的热障涂层（TBC）成功应用到燃气轮机制造业。在燃气轮机的热燃气领域，热障涂层满足了隔热的要求，从而降低了工件金属部分的温度。燃烧室的烧结温度超过1300摄氏度，而大部分金属材料的长期工作温度在950摄氏度左右，这样一来，就势必导致旋片，小叶片以及燃烧室部件在喷涂时的高要求。Typical thermal barrier coatings are multi-layer systems based on a duplex structure, a dense metallic bond coat layer (material: MCrAlY, M-Ni and/or Co) and a porous ceramic top coat layer (material: YSZ, yttrium-stabilized zirconia), shown in Fig. 1.典型的热障涂层是一个以复式结构为基础的多层系统，包括致密金属结合涂层（材料如：MCrAlY, M-Ni和/或Co），以及上层多孔陶瓷涂层（材料如：YSZ, 钇稳定氧化锆），如图1所示。Fig. 1. plasma coated TBC-coating system on turbine blade图1：轮机叶片上的热障涂层系统（等离子制备）The dense MCrAlY coating protects the base material against corrosion/oxidation and provides the connection for the ceramic top coat. The porous ceramic top coat functions in connection with the external and internal component cooling as a thermal barrier. Contrary to the dense MCrAlY coating a defined porosity of the YSZ coating is necessary to compensate strain difference and to reduce thermal conductivity. These specific requirements pose a challenge to the technology for producing such coating systems. MCrAlY致密涂层对母材起到了抗氧化防腐蚀作用，并同时实现了与表面陶瓷涂层的连接。表面多孔陶瓷涂层一来用于与里面的涂层相连，也为其所覆盖的内部部件形成了一个热障碍层，起到了冷却的作用。相对于MCrAlY致密涂层而言，固定孔隙率的YSZ涂层对拉力差异补偿及降低导热率来说是非常必要的。而这些特殊要求就对当今涂层生产技术提出了新的挑战。In addition to ensure coating quality, the manufacturing costs are more and more in focus of current developments.除涂层质量外，制造成本也越来越成为了当前发展的焦点问题。The production of porous YSZ coatings is done by Atmospheric plasma spraying (APS). Using this technology the plasma torch construction is one limiting factor for process improvements. For example voltage and power fluctuations influence the particle properties negatively 2, 3, 4. The use of cylindrical nozzle design limits the possibility of adjusting the plasma flow. By several new plasma torch concepts (multi-electrode, cascade, high power 5, 6, 7, 8) new characteristics are achieved which can contribute to a reduction in manufacturing cost. The traditional single-cathode-anode plasma torch based on F4/MC60 is the most widely-used system for years. Especially in turbine manufacturing this system is used for coating components with complex geometries and according to this targeted product extensive manipulation sequences of the plasma torch is required.多孔YSZ涂层通过大气等离子工艺（APS）进行喷涂。而采用该项技术进行工艺改造的关键限制因素是等离子枪的设计制造。如电压和电流的波动会影响到粉末颗粒的性能2, 3, 4。圆柱形喷嘴的使用限制了等离子流调整的可能性。通过采用一些新的设计理念（如多电极、串联方式，大功率等5, 6, 7, 8），等离子喷枪开发了一些新的性能，从而能达到降低生产成本的目的。基于F4/MC60基础上制造的传统单阴阳极等离子喷枪系统已经广泛推广并使用多年。特别是在轮机制造行业，该系统用于复杂工件的喷涂，因为工件结构复杂，等离子喷枪的安装工序就更繁杂一些。 For the coating process of turbine components with porous YSZ coating and a porosity class of 15%, the manufacturing costs excluding wear parts for a depreciated equipment like F4 with typical coating parameters are shown in Fig. 2.轮机部件的YSZ多孔涂层喷涂工艺（孔隙率大于15%）的成本计算在图12中做了图示说明，采用典型参数进行喷涂，费用中不包含部件磨损和F4这样的设备折旧费用。Fig. 2. cost allocation of APS process for porous YSZ coating, excluding wear parts anddepreciated equipment 图2：采用APS工艺制备多孔YSZ涂层的成本计算图，部件磨损及设备折旧费用不在计算范围内Plasma parameters with a total gas flow rate 30 slpm and an argon/hydrogen ratio of 4:1, as well as a electrical power of 30 kW result by a powder feed rate of 80 g/min in deposition efficiency (ratio of deposited powder weight to feeded powder weight = DE) of about 35%. In relation to current costs of employee, electricity, gases and powder, the YSZ powder usage is the major cost factor of the coating process. The increase in process efficiency by using the existing equipment with no change of coating quality (porosity, porosity distribution, coating thickness, stress, thermal-shock stability) is beneficial because no additional investment costs occur and a high degree of experience in handling the equipment is retained. A parallel use of already qualified coating processes with the existing equipment is possible as well. In this context an improvement of the plasma torch equipment based on a single-cathode-anode system with subsequent coating parameter optimization is done. Target is to realize a more efficient process with increased effective coating deposition. 等离子参数为：燃气总流量30 slpm，氧气/氢气比率为4:1，功率小于30kW，这是因为35%左右的沉积效率（粉末沉积重量除以送粉重量的比率=DE，送粉率）的送粉速度为80g/min。按照目前的人工、用电、燃气和粉末成本，YSZ粉末无疑是喷涂过程中的主要成本因素。通过使用现有喷涂设备，涂层质量保持不变（孔隙率、孔隙率分布、涂层厚度、应力、热震稳定性）的前提下，提高喷涂效率是非常有益的，因为并没有产生额外的成本，并且工人以往积累的设备操作经验也得以保留。更难能可贵的是，它并不影响在现有设备上使用以往的喷涂工艺。在这样的背景下，在单阴阳极系统上进行的喷枪改造以及喷涂参数优化工作得以进行。优化目标是通过增加涂层有效沉积率，从而达到提高生产效率的目的。2 Experimental Work 试验工作2.1 Motivation 试验动机The current coating process is based on the commercially widely spread single-cathode-anode system, such as F4/MC60. Assuming that a slow, high enthalpy plasma jet is necessary to produce a porous YSZ coating, the used equipment (plasma torch) with a cylindrical nozzle design (diameter 8mm) and a total gas flow rate less than 30 slpm is not optimal. A realized deposition efficiency of 35% leads to high powder consumption, increased coating times and results in high costs. Furthermore, due to the asymmetric plasma jet, the powder injection has to be adapted every production setup and adjusted to the plasma jet. Initial setup tests like spray spot analysis and coating of test parts for process controlling are needlessly complicated and cause high work load before production start and lead to additional costs.当前使用的涂层工艺是在商业上广泛推广的单阴阳极系统，如F4/MC60。假设制备多孔YSZ涂层时，需要慢速高焓值的等离子射流，那么以往总量小于30 slpm的燃气流量以及圆柱形喷嘴设计（直径为8mm）的设备（等离子喷枪）就不是很理想了。如果要达到35%的沉积效率，就意味着粉末用量增加，喷涂时间延长，并最终导致喷涂成本升高。此外，由于等离子流不对称，注粉时不得不调整工装以及粉末注入等离子流的角度。在正式生产前进行的初始工装测试，如喷涂点分析，对测试部件喷涂所做的工艺控制都造成了不必要的复杂以及高强度工作，从未最终导致了成本上升，费用增加。In order to simplify the setup procedure and to achieve time savings, a stable and consistent plasma jet is needed.Consequently, two main targets for optimization of the coating process can be defined.1. Improve of deposition efficiency of the coating process (to reduce the manufacturing costs)2. Generate a stable and consistent plasma jet (impact on indirect added value)One opportunity to influence process stability and plasma properties is the adjustment of the anode design which is functioning as a nozzle. Former investigations with different nozzle designs show a potential to increase the efficiency of the atmospheric plasma spraying 9.Based on these findings a new nozzle design was developed, which is adapted to the required boundary conditions for coating process of turbine components (minimum spray distance). This new nozzle configuration(VMT-nozzle) the basis for the following process optimization.为了简化工装并节省时间，等离子射流必须要稳定并连续。这样一来，涂层工艺优化的两大目标由此可以得到确定：1. 提高涂层工艺的沉积效率（降低生产成本）2. 制造连续稳定的等离子射流（影响间接附加值）影响生产稳定性以及等离子性能的其中一个方式是调整对阳极的设计（阳极作为喷嘴使用）。以往改变喷嘴设计的研究表明了通过此方法提高大气等离子喷涂效率的可能性【9】。在此基础上，我们设计了一个新型喷嘴，该新型喷嘴能很好的适应叶片部件的边界喷涂（最小喷距）。而该喷嘴的配置（VMT-喷嘴）是接下来工艺优化的前提和基础。2.2Optimization approach 优化过程Previous studies show a conflict between increasing the deposition efficiency and the need of a consistent coating porosity 10. By increasing the number and density of molten particle in the spray stream, the coating density increases and the required porosity decreases. Themain influencing factores are consequently temperature, velocity and distribution of particles in the spray stream. To realize an increased DE a possible approach is a holistic examination of the coating process, described in Fig. 3.之前的研究总是会在提高沉积效率和保持一致的涂层孔隙率之间相互矛盾【10】。通过在等离子射流中增加熔融颗粒的数量和浓度，可以达到涂层密度和孔隙率降低的目的。而主要的影响因素是等离子射流中粉末颗粒的温度，速度以及粒径分布。为了提高沉积效率，一个可行的办法是按照图3的程序对整个喷涂工艺进行全面的检查。Fig. 3. plasma coating process, using a single- cathode-anode system (e.g. F4 /MC60)图3：采用单阴阳极系统（如F4 /MC60）进行的等离子喷涂示意图， Potential influencing variables of the coating process optimizations are (elected):等离子喷涂工艺优化的潜在影响因素（选定的）a) Adjustment of plasma properties:Plasma enthalpy, -velocity, -viscosity, -density, - temperature modified byplasma gases, electrical power, voltage, voltage fluctuationsa) 等离子性能的调整：下列因素可以改变等离子焓值、速度、粘度、浓度、温度：等离子气体 电流、电压、电压波动b) Adjustment of particle properties: Particle grain size distribution, particle velocity, temperature modified by powder feedrate carrier gas flow injection conditionsb)粉末颗粒性能的调整: 下列因素可以改变粉末颗粒的粒径分布、速度以及温度：送粉率 载气流量 注粉情况c) Adjustment of coating deposition:Coating thickness, -porosity, - porosity distribution modified byspray distancemovement procedurerobot velocity, offset, number of layersc)涂层沉积的调整：下列因素可以改变涂层厚度、孔隙率以及孔隙分布情况：喷距行走程序机器人速度、偏差以及喷涂遍数1.3Experimental procedure 试验程序The first step of the optimization process focuses on increasing the deposition efficiency. The analysis are carried out by coating static spray spots. The second step involves an adaption of the coating properties (porosity/porosity distribution) and is realized by coating strings. A string is a coating which is produced by a vertical movement of the robot (constant robot speed) with no horizontal offset and therefore with no overlapping of paths. 工艺优化的第一步就是提高沉积效率。研究分析是在固定喷涂点上进行的。第二步则是改变涂层性能（孔隙率/孔隙率分布）并通过涂层列来实现。涂层列是指通过机器人（机器人速度恒定）垂直运动来进行喷涂所制备的涂层，无水平偏差，因此不会产生涂层重叠的情况。Test series a) Adjustment of plasma properties:test objects = spray spotsDevelopment target = increasing of DE to maximum 试验A系列) 等离子性能的调整 试验对象=喷涂点 试验目的=将沉积率提高到最大值By a theoretical assumption that the particle velocity should be slow as possible to generate a high porous coating, it is necessary to reduce the total gas flow rate to a minimum. Furthermore a high temperature of the plasma jet is favoured to raise the percentage of molten particles and through this an increasing of deposition efficiency. This fact is influenced by changing the content of molecular gas (hydrogen) in the plasma. The test series to optimize DE are done by constant coating distance, constant electrical power, constant powder feed rate.从理论上假定，如果需要制备多孔涂层，则粉末速度需要越慢越好，如降低粉末速度，则总燃气流量必须要降至最低。另外，等离子射流的温度越高，粉末熔融的比率就会越高，这样一来，沉积率也相应得到提高。但改变等离子流中分子气体（氢气）含量可以影响该情况。通过恒定喷涂距离、恒定电流以及恒定送粉率来实现沉积率优化系列的实验。The powder feed rate of the standard coating process with 80 g/min has been used. To achieve the minimum coating distance the plasma properties-velocity, temperature are influenced by varying total gas flow rate and argon/hydrogen ratio. Results of these test series are shown in Fig. 4.标准喷涂工艺使用80g/min的送粉率。为了达到最小的喷涂距离，通过改变气体总流量以及氩气和氢气的比率来调节等离子性能（速度和温度）。该系列试验的结果如图4所示：Fig. 4. influence of argon/hydrogen ratio and total gas flow to DE, P=30kW 图4: 氩气/氢气比率及总气流对沉积率的影响，P=30kWIn consideration of anode and cathode wear and a limitationof the used equipment,a ratio of argon/hydrogen of 4:1 and a total gas flow rate of 37.5 slpm are chosen. The geometry of the VMT nozzle leads to a reduction of length of the emitted plasma jet compared to the cylindrical nozzle, Fig.5. During the previous tests it becomes clear that the present injection condition of 100 in plasma flow direction is not the optimum for the VMT nozzle.考虑到阳极和阴极的磨损以及所使用设备的限制，选择4:1的氩气/氢气比率，气体总流量为37.5 slpm。如图5所示，相对于圆柱形喷嘴，我们设计的几何形状的VMT喷嘴减小了等离子流发散的长度。按照之前的试验结果，目前的100度并不是VMT喷嘴的最佳注入角度。Fig. 5. Images of plasma jets standard (top) vs. optimized (button)图5：标准等离子流（上图）与优化后的等离子对比效果图（下图）Due to this the powder injection point is placed closer to the nozzle exit, the injection angle is changed from 100 to 90 in flow direction. The result is a longer exposure time of particles in the plasma jet resulting in an enhanced melting behaviour, the DE increases from 28% to 46%.由于这样的原因，注粉点设置得离喷嘴出口更近，而注粉角度就从顺流方向100度变为90度。这样一来，等离子流中粉末颗粒的暴露时间就会延长，那么粉末熔融情况得以加强，沉积效率从28%增加到46%。For the selected plasma parameter and powder injection condition the DE is optimized related to the adjustment of electrical power, Fig. 6.在选定等离子参数及注粉条件的情况下，如图6所示，通过调整电流达到提高沉积效率的目的。Fig.6. influence of electrical power variations on DE and arc voltage, powder A图6： 电源调整对沉积率以及电弧电压的影响示意图，粉末AFor the investigated electrical power range the arc voltage is almost constant The associated constant arc lengthindicatesa fixationof the anode attachement (arc) inside the nozzle.In first assumption this effect is caused by the geometry of the nozzle and due to this the specific fluid dynamics of the generated plasma flow. Tab. 1 shows a comparison of specific plasma parameters, standard vs. improved (VMT).按照我们研究的电流范围，电弧电压是最稳定的。稳定的电弧长度表明喷嘴内部阳极（电弧）的稳定情况。我们首先假定是几何形喷嘴对阳极的影响造成的。以及由此产生的等离子流的特殊流动性，表1中是标准喷嘴及改进后的喷嘴（VMT），在特定等离子流参数下的对比情况。Tab.1 comparison of charcteristical plasma parameters of the standard and optimized process(VMT)表1：标准喷嘴及优化喷嘴的等离子性能参数对比表StandardVMTArgon/hydrogen ratio4:14:1Electrical power kW2737Plasma voltage V5863Voltage fluctuations V2211Thermal efficiency %4249标准喷嘴优化后喷嘴氩气/氢气比率4:14:1电源kW2737等离子电压V5863电压波动 V2211热效应 %4249Test series b) Adjustment of particle properties:test objects = spray spots and stringsdevelopment target = maximization of DE and porosity adjustment 试验b系列)颗粒性能调整:试验对象=喷涂点及喷涂行 试验目标=将沉积率增加到最大，并实现孔隙率的调整Using the optimized plasma- and injection parameters from test series a), the porosity for constant coating distance decreases below the minimal accepted level. To counteract, the porosity is adjusted by optimizing grain size distribution of the spray powder and coating distance. The standard used YSZ powder shows a grain size distribution of -125+22 m (powder A). In order to achieve a higher porosity level, the fine fraction is removed and a grain size distribution of -125+44m (powder B) is determined as the optimum distribution. Furthermore, the coating distance is optimized to 160 mm. By adjusting the grain size distribution, the porosity is increased from 13% (powder A) to a required porosity level of approx. 20% (powder B).采用试验a系列中的优化等离子及注粉参数，由于恒定喷涂距离的降低，孔隙率得以降到最低可接受水平。为了应对此情况，通过优化粉末颗粒的粒径分布以及喷涂距离，可以对孔隙率进行调节。标准工艺中使用的YSZ粉末的粒径分布范围为-125+22 m (粉末A). 为了达到更高的孔隙率水平，去掉较细颗粒部分，我们决定采用-125+44m（粉末B）作为优化后的粒径分布。此外，优化后的喷涂距离为160mm。通过调整粒径分布范围，孔隙率从13%（粉末A）增加到所需的20%左右（粉末B）。Due to the present development results, it is possible to deduce an optimized parameter set for coating of porous YSZ with specific porosity level.按照目前的研究结果，可以推导出通过优化参数设置，达到YSZ涂层所要求的孔隙率水平。To characterize the particle properties (velocity, temperature) of both coating parameters (standard, improved)SprayWatch measurements are carried out. The comparative analysis clarifies a difference in particle velocity: for the optimized coating parameter the velocity is reduced by approx. 10 m/s compared to the standard parameter, Fig. 7. 通过Spraywatch对两种喷涂参数（标准及优化后的）进行颗粒速度和温度的测量。分析对比表明颗粒速度的区别为：如图7所示，与标准工艺参数相比，优化后喷涂参数的颗粒速度降低了大概10m/s.The measurements of particle temperatures show similar values for both parameters at specific coating distances, Fig. 8.在喷涂距离一定的情况下，而所测量到的两种参数的颗