Ceramic Top Coats of Plasma-Sprayed Thermal Barrier Coatings: Materials,Processes, and Properties

The ceramic top coat has a major influence on the performance of the thermal barrier coating systems (TBCs). Yttria-partially-stabilized zirconia (YSZ) is the top coat material frequently used, and the major deposition processes of the YSZ top coat are atmospheric plasma spraying and electron beam physical vapor deposition. Recently, also new thermal spray processes such as suspension plasma spraying or plasma spray-physical vapor deposition have been intensively investigated for TBC top coat deposition. These new processes and particularly the different coating microstructures that can be deposited with them will be reviewed in this article. Furthermore, the properties and the intrinsic–extrinsic degradation mechanisms of the YSZ will be discussed. Following the TBC deposition processes and standard YSZ material, alternative ceramic materials such as perovskites and hexaaluminates will be summarized, while properties of pyrochlores with regard to their crystal structure will be discussed more in detail. The merits of the pyrochlores such as good CMAS resistance as well as their weaknesses, e.g., low fracture toughness, processability issues, will be outlined.     

涂层结构对建筑节能涂层性能的影响

目的通过探究建筑节能涂层的最佳涂层结构,进而提升涂层的隔热和耐久性能。方法将含空心微珠和二氧化钛的涂层作底漆,硅溶胶-苯丙复合涂层作面漆,探究不同种类底漆和面漆对铬绿建筑节能涂层性能的影响。采用正交试验寻求最佳底漆和面漆组合方案,对最佳组合方案涂层进行了综合性能测试,并探讨了相关机理。结果在不改变涂层颜色外观的情况下,底漆可增加涂层的太阳光反射比,面漆可增大涂层的静态接触角,增强涂层的耐水性、耐沾污性和耐老化性,降低涂层污染后和人工气候老化后太阳光反射比变化率及色差。最佳涂层结构组合方案为:底漆中空心微珠和二氧化钛掺量均为5%,面漆中苯丙乳液和硅溶胶质量比为14∶1。此时涂层的太阳光反射比和隔热温差分别为0.6455和6.9℃,且综合性能均较好,具有一定的应用价值。结论涂层结构对建筑节能涂层的隔热和耐久性能具有一定的影响,实际应用时可根据需要改变涂层结构来获得满意的性能。     

DETERMINATION OF CREEP PROPERTIES OF THERMAL BARRIER COATING（TBC） SYSTEMS FROM THE INDENTATION CREEP TESTING WITH ROUND FLAT INDENTERS

Indentation creep behavior with cylindrical flat indenters on the thermal barrier coating (TBC) was studied by finite element method (FEM). On the constant applied indentation creep stress, there is a steady creep rate for each case studied for different creep properties of the TBC system. The steady creep depth rate depends on the applied indentation creep stress and size of the indenters as well as the creep properties of the bond coat of the TBC and the substrate. The possibilities to determine the creep properties of a thermal barrier system from indention creep testing were discussed. As an example, with two different size indenters, the creep properties of bond coat of the TBC system can be derived by an inverse FEM method. This study not only provides a numerical method to obtain the creep properties of the TBC system, but also extends the application of indentation creep method with cylindrical flat indenters.     

电火花表面强化工艺的参数优化

研究了Ti合金表面电火花强化WC过程中,影响强化层厚度的因素及其规律性。认为电容两端输出电压、充电电容量、比强化时间、保护气体流量、电极旋转速度是影响强化层厚度的主要因素。通过合理的参数优化,可以在Ti合金表面获得平均厚度大于100mm的WC-Co8强化层。     

结晶器保护渣的润滑与传热控制功能剖析

对保护渣渣膜在润滑与控制传热两个方面的功能发挥进行了剖析,如黏-温曲线、转折温度,渣膜结晶状态和析出相进行了研究,并指出渣膜的转折温度、结晶率对润滑功能发挥起主要作用;而渣膜的闭孔率、表面粗糙度、枪晶石比例对控制传热功能具有关键性的影响。同时,对3种典型保护渣的渣膜凝固特性进行了研究,讨论了与钢种特性和连铸工艺相适应的保护渣基本性能参数,如碱度、熔点、黏度、转折温度、烧结性能、渣膜中气体等对发挥润滑与控制传热两个功能的影响。提出了保护渣管理方面需要重点控制的内容,如保护渣全水含量高低,生产过程中更换不同性能保护渣对传热与润滑的持续影响,液渣池深度的合理值等。     

Properties of plasma-sprayed bond coats

Increasing bond coat oxidation resistance has been clearly linked to increasing durability of the ceramic layer of thermal barrier coatings (TBCs). However, recent studies have shown that significant differences in TBC life can be achieved for different bond coats that exhibit little or no difference in oxidation behav-ior. These data suggest that bond coat properties other than oxidation resistance can also influence TBC life. Determination of which properties affect TBC life and how they do so could be valuable in designing new, more durable TBCs. This paper reviews the results of comparative studies of the properties of three bond coat compositions that have similar oxidation behavior but different TBC lives. An analysis of the properties indicates that the thermal cycle residual stress, calculated from the coefficient of thermal ex-pansion and the stress relaxation behavior of the three alloys, is strongly correlated to the observed dif-ferences in TBC life.     

带MoS2涂层轴承的腐蚀失效分析

本文对某带MoS2涂层轴承的腐蚀现象进行了试验分析,并根据试验结果讨论了带MoS2涂层构件的腐蚀防护问题。通过对失效轴承的宏微观形貌观察、微区成分分析、金相检查以及耐蚀性对比试验,明确了轴承的失效性质。结果表明：带MoS2涂层的GCr15钢滚珠发生了膜下丝状腐蚀。除了采用控制腐蚀环境和提高涂层致密性等方法外,选择更耐蚀的构件材料或者通过表面防腐处理是提高带MoS2涂层构件防腐能力的有效途径。     

Molecular Dynamics Simulation of Flattening Process of a High-Temperature, High-Speed Droplet—Influence of Impact Parameters

Three-dimensional molecular dynamics simulation was conducted to clarify at an atomic level the flattening process of a high-temperature droplet impacting a substrate at high speed. The droplet and the substrate were assumed to consist of pure aluminum, and the Morse potential was postulated between a pair of aluminum atoms. In this report, the influence of the impact parameters such as the droplet velocity and the droplet diameter on flattening behavior were analyzed. As a result, the following representative conclusions were obtained: (a) the flattening ratio increases in proportion to the droplet velocity and the droplet diameter; (b) the flattening ratio for nanosized droplet can be reorganized by the same dimensionless parameters of the proper physical properties, such as the viscosity and the surface tension, as those used in the macroscopic flattening process. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously 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, OH, 2007.     

Nanocomposite Protective Coatings Fabricated by Electrostatic Spray Method

Nowadays, powder coating can be used for many application, especially for protection against corrosive environments. Powder coating is usually done with using an electrostatic device and spraying gun. With using this method, a thin film layer is created on the surface which can play decorative or protective role. In this paper, the effect of some factors such as size of powder, charging, voltage, air flow, gun distance, charge–to-mass ratio, feed rate, coating functionality, glass transition temperature (T_g), viscosity, catalyst, temperature and curing time on the coating properties and their influence on the coating were mentioned. In recent years, nano composite polymers have been considered severely. Coating properties are improved by adding nanoparticles such as clay, SiO₂, TiO₂ and Al₂O₃ to the polymer composition. These coatings are used for reducing the gas permeability, thermal stability, optical clarity and increasing the mechanical and corrosion properties of coatings also these coatings have high mechanical properties that can be pointed to its high abrasion resistance. In this paper, the corrosion properties and the effect of adding nanoparticles on the corrosion resistance properties of powder coatings have been investigated, also the mechanical properties of powder coatings were reviwed.     

Effect of reprocessing on shrinkage and mechanical properties of ABS and investigating the proper blend of virgin and recycled ABS in injection molding

In this research, the effect of reprocessing of acrylonitrile–butadiene–styrene (ABS) on the mechanical properties of the polymer was studied through a five-stage reprocessing. To this end, the injection mold of the standard samples was manufactured. Then, using an injection molding machine, all of the virgin material was processed. After sampling, the rest of the parts were ground and then reprocessed under the same conditions. In order to get a proper combinational ratio of virgin and recycled ABS with respect to shrinkage and mechanical properties, another experiment was designed. In order to do this, virgin material was blended with 20%, 35% and 50% of the recycled material. The blends were reprocessed and samples were obtained. Impact, tensile, flexural and shrinkage tests, selected from ASTM standard, were used to investigate the mechanical properties of the polymer as well as its shrinkage. Furthermore, viscosity test was used to investigate the changes in the structure of the polymer. As the reprocessing cycles increased, shrinkage decreased and tensile and flexural ultimate strengths increased, more in flexural strength than in tensile. While Young's modulus slightly increased, viscosity decreased and consequently molecular weight decreased too. The proper blend for the least shrinkage was 50% whereas the best mechanical properties were achievable by the 20% blend. The obtained results suggest that reprocessing causes polymer degradation which is a result of the break in the bonds of poly butadiene. Moreover, it can be concluded that reprocessing in ABS can lead to the loss of effectiveness of some additives.     

反应体系粘度对多元醇法制备银纳米线的影响

在多元醇还原制备银纳米线(AgNW)的反应中,聚乙烯吡咯烷酮(PVP)稳定剂发挥着“软模板”的作用。通过加入不同相对分子量的PVP,研究其加入量对制备AgNW的影响。结果表明,PVP通过改变体系的粘度影响AgNW的直径、线长和产率。在一定粘度范围内(2.5~7.5 mPa.s),AgNW的直径基本稳定(约30 nm);线长大致随反应体系粘度增加呈现先增后减的趋势,最长平均线长在中间粘度(约3 mPa.s)获得,其中加入PVP K60时可在中间粘度获得最大平均线长(16 nm);粘度通过控制溶液中的传质作用影响副产物比例,当粘度很低(<2.5 mPa.s)或很高(>7.5 mPa.s)时,颗粒和短棒副产物比例大。     

稀土铈对化学复合镀Ni—P—Si3N4工艺及性能的影响

研究稀土铈对Ｎｉ－Ｐ－Ｓｉ３Ｎ４化学复合镀工艺操作性能及镀层性能的影响,发现在Ｎｉ－Ｐ－Ｓｉ３Ｎ４化学复合镀镀液中加入少量稀土铈能有效地提高镀速及镀液稳定性,并可以提高镀层中ＳｉＮ的共沉积量,增加镀层硬度,但镀层耐蚀性有所下降,镀层结构分析发现镀层由非晶态向微晶态转变。     

An evaluation of the electric arc spray and (HPPS) processes for the manufacturing of high power plasma spraying MCrAIY coatings

The high power plasma torch (PlazJet) can be used to spray refractory ceramics with high spray rates and deposition efficiency. It can provide dense and hard coating with high bond strengths. When manufacturing thermal barrier coatings, the PlazJet gun is well adapted to spraying the ceramic top coat but not the MCrAIY materials that are used as bond coat. Arc spraying can compete with plasma spraying for metallic coatings since cored wires can be used to spray alloys and composites. In addition, the high production rate of arc spraying enables a significant decrease in coating cost. This paper discusses the performances of the PlazJet gun, and a twin-wire are spray system, and compares the properties and cost of MCrAIY coatings made with these two processes. For arc spraying, the use of air or nitrogen as atomizing gas is also investigated.     

Influence of TGO Composition on the Thermal Shock Lifetime of Thermal Barrier Coatings with Cold-sprayed MCrAlY Bond Coat

NiCoCrAlTaY bond coat was deposited by cold spraying to assemble thermal barrier coatings (TBCs). The microstructure of the cold-sprayed bond coat was examined using scanning electron microscopy. TBCs consisting of cold-sprayed bond coat and plasma-sprayed YSZ were pretreated at different conditions to form different thermally grown oxides (TGOs) before thermal cycling test. The influence of the TGO composition on the thermal cyclic lifetime was quantitatively examined through the measurement of the coverage ratio of the mixed oxides on the bond coat surface. The results showed that the bond coat exhibited a dense oxidation-free microstructure, and TGOs in different morphologies and constituents were present after thermal cyclic test. The formation of TGOs was significantly influenced by pretreatment conditions. Two kinds of TGO were detected on the surface of bond coat after the spallation of YSZ coatings. One is the α-Al₂O₃-based TGO and the other is the mixed oxide. It was found that the thermal cyclic lifetime is inversely proportional to the coverage ratio of the mixed oxides formed at the bond coat/YSZ interface. The high coverage ratio of the mixed oxide on the interface leads to the early spalling of YSZ coating.     

钢桥面沥青混凝土铺装层下热喷锌涂层的腐蚀行为

研究了钢桥面沥青混凝土铺装层下热喷锌防腐蚀涂层的腐蚀特征,并在此基础上提出锌涂层腐蚀导致沥青混凝土铺装层性能下降的理论假设模型。采用IM6ex电化学工作站研究了热喷锌涂层的腐蚀电位、腐蚀电流与时间的关系,涂层的极化特性,采用XRD分析了锌涂层的腐蚀产物。结果表明锌涂层腐蚀产物中存在大量ZnO和Zn5(CO3)2(OH)6,破坏了粘结层与锌涂层之间的粘结,起到裂纹源的破坏作用,使铺装层在载荷的作用下提前失效。     

On the development of plasma-sprayed thermal barrier coatings

Various zirconate coatings were prepared on bare Nimonic-75 and on CoCrAlY bond coat by plasma spraying. The cyclic oxidation and hotcorrosion resistance of these coatings have been evluated. The wide difference in the properties of these coatings has been rationalized in terms of the thermal expansion mismatch between the coating and the substrate. On continued thermal cycling and in presence of molten salt, the life-limiting factor has been identified to be oxidation of the bond coat. The interconnected porosity in the ceramic coating is mainly responsible for such oxidation, and controlling this porosity would lead to life improvement.     

Rheological properties of metal injection molding feedstock

Viscosity of a polyethylene glycol-polymethyl methacrylate (PEG-PMMA) binder and PEG-PMMA/Fe-2Ni feedstock in powder injection molding was measured and calculated. A logarithmic additivity between viscosity of the binder and that of its constituents was found. Other factors, such as temperature, powder loads, content and type of surface-active agents and those of polymers, in relation to rheological properties of feedstock were discussed as well. The results showed that with increasing viscosity of surface-active agent, polymer melt index or temperature, the feedstock viscosity decreased while higher polymer content and powder loading would lead to additional feedstock viscosity. The relationship mentioned above is expressed and effectively explained why the change rate of feedstock viscosity will slow down with the increase of shear rate.     

热喷涂、喷熔层抗磨性研究

热喷熔和热喷涂技术被广泛应用于机件的耐磨强化。按涂层材料和工艺的不同会得到不同组织和性能的涂层，研究评价这些涂层在磨粒磨损和冲蚀磨损中的抗磨能力及规律性，可为工程应用提供一定的指导。     

含钛夹杂物对连铸保护渣性能的影响

含钛钢连铸过程中析出氮化钛夹杂,并参与渣-金界面反应,严重恶化传统含钛钢连铸保护渣的理化性能。研究了不同含量的TiN和TiO₂对不同碱度保护渣的熔点、黏度、结晶比例以及凝固温度等性能的影响规律。测试结果表明,TiN对CaO-SiO₂基保护渣的性能影响最大,随着渣中TiN含量的升高,保护渣的黏度、结晶比例和凝固温度大幅度升高;当TiN质量分数大于5%时,熔点大幅升高。TiO₂对CaO-Al₂O₃基保护渣的性能影响最大,当TiO₂质量分数小于4%时,可小幅度降低保护渣的黏度和凝固温度;当TiO₂质量分数大于10%时,渣中钙钛矿成为主要析出物相,熔渣的性能严重恶化,影响对坯壳的润滑作用。通过对比3种不同碱度的基础渣发现,CaO-SiO₂-Al₂O₃基保护渣具有较好吸收含钛夹杂物的能力。     

Adhesion improvements of Thermal Barrier Coatings with HVOF thermally sprayed bond coats

Thermal barrier coatings (TBC) are an effective engineering solution for the improvement of in service performance of gas turbines and diesel engine components. The quality and further performance of TBC, likewise all thermally sprayed coatings or any other kind of coating, is strongly dependent on the adhesion between the coating and the substrate as well as the adhesion (or cohesion) between the metallic bond coat and the ceramic top coat layer. The debonding of the ceramic layer or of the bond coat layer will lead to the collapse of the overall thermal barrier system. Though several possible problems can occur in coating application as residual stresses, local or net defects (like pores and cracks), one could say that a satisfactory adhesion is the first and intrinsic need for a good coating. The coating adhesion is also dependent on the pair substrate-coating materials, substrate cleaning and blasting, coating application process, coating application parameters and environmental conditions. In this work, the general characteristics and adhesion properties of thermal barrier coatings (TBCs) having bond coats applied using High Velocity Oxygen Fuel (HVOF) thermal spraying and plasma sprayed ceramic top coats are studied. By using HVOF technique to apply the bond coats, high adherence and high corrosion resistance are expected. Furthermore, due to the characteristics of the spraying process, compressive stresses should be induced to the substrate. The compressive stresses are opposed to the tensile stresses that are typical of coatings applied by plasma spraying and eventually cause delamination of the coating in operational conditions. The evaluation of properties includes the studies of morphology, microstructure, microhardness and adhesive/cohesive resistance. From the obtained results it can be said that the main failure location is in the bond coat/ceramic interface corresponding to the lowest adhesion values.