Manufacturing Process of Nanostructured Alumina Coatings by Suspension Plasma Spraying

This paper describes the formation process of nanostructured alumina coatings and the injection system obtained by suspension plasma spraying (SPS), an alternative to the atmospheric plasma spraying technique in which the material feedstock is a suspension of the nanopowder to be sprayed. The nanoscale alumina powders (d ≈ 20 nm) were dispersed in distilled water or ethanol and injected by a peristaltic pump into plasma under atmospheric conditions. Optical microscopy (OM), scanning electron microscopy (SEM), and x-ray diffraction (XRD) analyses were performed to study the microstructure of the nanostructured alumina coatings. The results showed that the nanoscale alumina powders in suspension were very easily adsorbed at the inner surface of injection, which caused the needle to jam. The rotation of the pump had a great effect on the suspension injection in the plasma. The very small resistance of the thin plasma boundary layer near the substrate can drastically decrease the impacting velocity of nanosize droplets. The concentration of suspension also has a significant influence on the distribution of the size of the droplet, the enthalpy needed for spraying suspension, and the roughness of the coating surface. The phase structures of alumina suspension coatings strongly depend on the plasma spraying distance. A significant nanostructured fine alumina coating was obtained in some areas when ethanol was used as a solvent. The microstructures of the coating were observed as a function of the solvent and the spraying parameters.     

Influence of Suspension Plasma Spraying Process Parameters on TiO2 Coatings Microstructure

The study aimed at optimizing the suspension plasma spraying of TiO₂ coatings obtained using different suspensions of fine rutile particles in water solution onto aluminum substrates. The experiments of spraying were designed using a 2³ full factorial plan. The plan enabled to find the effects of three principal parameters, i.e. electric power input to plasma, spray distance, and suspension feed rate onto microstructure of coatings, content of anatase phase and size of anatase crystals in the coatings. The microstructure of deposits was observed with scanning electron microscope (SEM) and optical microscope and their composition was characterized using energy dispersive spectrometry (EDS). The observations were made on the coatings surface and their cross-sections. The latter made it possible to determine the coatings thicknesses to be in the range from 8 to 33 μm.

Suspension Plasma Spraying of YPSZ Coatings: Suspension Atomization and Injection

Among processes evaluated to produce some parts of or the whole solid-oxide fuel cell, Suspension Plasma Spraying (SPS) is of prime interest. Aqueous suspensions of yttria partially stabilized zirconia atomized into a spray by an internal-mixing co-axial twin-fluid atomizer were injected into a DC plasma jet. The dispersion and stability of the suspensions were enhanced by adjusting the amount of dispersant (ammonium salt of polyacrylic acid, PAA). A polyvinyl alcohol (PVA) was further added to the suspension to tailor its viscosity. The PVA also improved the dispersion and stability of the suspensions. The atomization of optimized formulations is described implementing Weber and Ohnesorge dimensionless numbers as well as gas-to-liquid mass ratio (ALR) value. Drop size distributions changed from monomodal distributions at low We to multimodal distributions when We number increases. The viscosity of the suspensions has a clear influence on the drop size distribution and suspension spray pattern. The secondary fragmentation of the drops due to the plasma jet was evidenced and the final size of the sheared drops was shown to depend on the characteristics of the suspension. Rather dense zirconia coatings have been prepared, which is a promising way to produce electrolyte.     

Suspension plasma spraying of nanostructured WC-12Co coatings

Nanostructured WC-12% Co coatings were deposited by suspension plasma spraying of submicron feedstock powders, using an internal injection plasma torch. The liquid carrier used in this approach allows for controlled injection of much finer particles than in conventional thermal spraying, leading to thin coatings with a fine surface finish. A polyethylene-imine (PEI) dispersant was used to stabilize the colloidal suspension in an ethanol carrier. In-flight particle states were measured for a number of operating conditions of varying plasma gas flow rates, feed rates, and standoff distances and were related to the resulting microstructure, phase composition (EDS, SEM, XRD), and Vickers hardness. High in-flight particle velocities (>800 m/s) were generated, leading to dense coatings. It was observed that the coating quality was generally compromised by the high temperature and reactivity of the small particles. To compensate for this shortcoming, the suspension feed rate was adjusted, thereby varying the thermal load on the plasma. Results showed that a slightly larger agglomerate size, in conjunction with low particle jet temperatures, could somewhat limit the decomposition of WC into brittle W₂C/W₃C and amorphous cobalt containing binder phases. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

水和乙醇悬浮液等离子喷涂SOFC电解质层的工艺及涂层特点比较

选用水和乙醇两种溶剂配置悬浮液,研究了分散剂PAA含量对(Ce0.80Gd0.20)O1.9(GDC)悬浮液粘度的影响和pH值对GDC颗粒Zeta电位的影响。采用固相质量分数为10%的GDC悬浮液等离子喷涂制备固体氧化物燃料电池电解质层。利用X射线衍射、扫描电镜和电子探针分别分析了喷涂前后GDC的相结构、电解质层微观组织及化学成分。研究结果表明:水悬浮液优化参数PAA质量分数为2.5%,pH=10;乙醇悬浮液优化参数为:PAA质量分数为2.0%,pH=10。在相同喷涂工艺下,乙醇悬浮液得到的电解质层结构更精细,由图像分析法得水和乙醇悬浮液得到电解质层的孔隙率分别为5.64%和1.25%。GDC喷涂前后没有相结构的变化,但是晶粒有长大,并且在喷涂过程中氧化铈发生烧损,水和乙醇悬浮液制备的电解质层中氧化铈分别烧损了15.8%和16.8%。     

等离子喷涂纳米结构n-Al2O3/Ni涂层性能研究

采用化学方法在纳米Al2O3颗粒表面包覆了一层Ni，通过喷雾干燥法制成了纳米结构热喷涂喂料。采用等离子喷涂工艺在45钢试样上制备了纳米结构n-Al2O3／Ni涂层，并对涂层的性能和结构进行了试验分析。结果表明，粒子飞行过程中存在“爆破”及物质迁移现象；涂层结构疏松多孔，与基体平均结合强度低；喷涂过程发生了由α-Al2O3向У-Al2O3的转变；与电弧喷涂类似3Cr13钢成分涂层相比，n-Al2O3／Ni涂层耐磨性显著提高，摩擦系数降低，主要的磨损形式是伴随疲劳磨损的粘着磨损。     

高效能超音速等离子喷涂粒子特性及涂层特点

超音速等离子喷涂技术是热喷涂技术的关键技术之一.从基础及应用的角度,研究了高效能超音速等离子(HEPJet)喷涂粒子的特性,探讨了高效能超音速等离子在制备Ni/Al等金属及其合金涂层、WC-Co金属陶瓷涂层、ZrO2等氧化物陶瓷涂层上的特点.结果表明,高效能超音速等离子喷涂系统具有焰流温度高、射流速度快等特点;制备的涂层粒子变形充分,涂层均匀,孔隙率低,结合强度高,涂层质量好;可将适用于喷涂的所有粉末材料制备成高质量涂层.     

Influence of Plasma Instabilities in Ceramic Suspension Plasma Spraying

Direct current Suspension Plasma Spraying (SPS) allows depositing finely structured coatings. This article presents an analysis of the influence of plasma instabilities on the yttria-stabilized suspension drops fragmentation. A particular attention is paid to the treatment of suspension jet or drops according to the importance of voltage fluctuations (linked to those of the arc root) and depending on the different spray parameters such as the plasma forming gas mixture composition and mass flow rate and the suspension momentum. By observing the suspension drops injection with a fast shutter camera and a laser flash sheet triggered by a defined transient voltage level of the plasma torch, the influence of plasma fluctuations on jet or drops fragmentation is studied through the deviation and dispersion trajectories of droplets within the plasma jet. 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.     

悬浮液等离子喷涂高效制备TiO2涂层及其光催化性能

目的 解决TiO2粉末催化剂在污水净化过程中易沉降和难回收问题,同时提高TiO2在可见光条件下降解有机污染物的速率。方法 采用悬浮液等离子喷涂(SPS)技术,以H2为辅助气体制备TiO2涂层,借助H2将高温等离子体焰流中熔融态TiO2中的Ti⁴⁺还原成Ti³⁺。通过场发射扫描电子显微镜、X射线衍射仪、X射线光电子能谱光谱仪、紫外-可见光谱仪等对TiO2粉末以及所制备涂层的结构形貌、物相组成、元素价态、光学特性进行分析。以亚甲基蓝为目标污染物,使用光化学反应仪测试粉末和涂层的光催化性能。结果 TiO2涂层表面呈现由熔融和半熔融颗粒组成的“喀斯特”微观形貌,表面粗糙度为2.94 µm,孔隙率为10.2%。TiO2粉末物相为纯锐钛矿,涂层物相由锐钛矿、金红石相及TiO2－x相组成。TiO2涂层中Ti³⁺的存在使其带间隙减小0.6 eV。在紫外光条件下,TiO2粉末的催化速率为0.003 48,而涂层的催化速率为0.003 45。在可见光条件下,粉末的催化速率与亚甲基蓝的光解速率相近,涂层的催化速率是0.003 07。结论 通过SPS技术成功制备了TiO2光催化涂层,其在可见光条件下的催化性能较粉末有显著提升。     

等离子喷涂TiC—Ni—Mo金属陶瓷涂层结构与性能的研究

在４５钢基材上用等离子喷涂方法制备了ＴｉＣ－Ｎｉ－Ｍｏ金属陶瓷涂层,对涂层进行了性能试验,ＳＥＭ分析及ＸＲＤ分析,结果表明,等离子喷涂ＴｉＣ－Ｎｉ－Ｍｏ金属陶瓷涂层组织是均匀的,涂层硬度达到９０ＨＲＡ。涂层经频率为１６次／ｍｉｎ,６０ｍｉｎ落球冲击试验后,显微镜下未见到任何剥离痕迹或裂纹,经比较试验,该涂层的结合强度和韧性优于同样基材上等离子喷涂的ＺｒＯ２陶瓷梯度涂层。     

High-Velocity Suspension Flame Spraying (HVSFS), a new approach for spraying nanoparticles with hypersonic speed

The fabrication of nanostructured coatings by means of thermal spray techniques is a challenging approach with new applications in mind. However, it requires the processing of very fine-grained powders with a grain size in the nanoscale. As nano- and submicrometer powders cannot be processed using mechanical powder feeders, new concepts have to be developed. Among these, suspension spraying is one of the most promising.High-velocity suspension flame spraying (HVSFS) is a new approach to spray micron, submicron or nanoparticles with hypersonic speed with the aim to form thin and dense coating layers. For this purpose, the powder is dispersed in aqueous or organic solvent and fed axially into the combustion chamber of a modified High-Velocity Oxyfuel (HVOF) spray torch. Several suspension feeder concepts were tested to ensure a constant flow of the suspension and, thus, a stable spray process.Different oxide materials were processed in form of a suspension containing submicrometer- or nanosized powders consisting of alumina, titania and yttrium stabilized zirconia (YSZ). The paper gives an introduction to HVSFS technology and will present first experimental results.     

轴向送粉式等离子喷涂陶瓷涂层工艺性能研究

对比研究了新型轴向送粉等离子涂枪和普通等离子喷涂枪的喷涂工艺参数和制备涂层的性能及其组织。试验结果表明：轴向送粉式等离子喷涂枪的功率明显低于普通等离子喷涂枪,其喷的陶瓷涂层的性能优于普通等离子喷涂。     

反应等离子喷涂TiN的反应过程及涂层形成机理研究

采用反应等离子喷涂技术制备了TiN涂层,并收集了少量TiN颗粒;采用SEM对涂层和TiN颗粒的横断面肜貌进行分析,研究了喷涂过程中的反应过程和涂层的形成过程.结果表明:Ti粉与N_2的反应为燃烧合成反应.反应过崔中释放出大量的热量,此反应在颗粒的表面进行;TiN涂层具有典型的层状组织结构,且层与层之间结合较好.     

Preparation of Aluminum Coatings Containing Homogenous Nanocrystalline Microstructures Using the Cold Spray Process

Nanostructured materials are of widespread interest because of the unique properties they offer. Well-proven techniques, such as ball milling, exist for preparing powders with nanocrystalline microstructures. Nevertheless, consolidation of nanocrystalline powders is challenging and presents an obstacle to the use of nanocrystalline metals. This work demonstrates that nanocrystalline aluminum powders can be consolidated using the cold spray process. Furthermore, transmission electron microscopy (TEM) analysis of the nanocrystalline cold spray coatings reveals that the cold spray process can cause significant grain refinement. Inert gas atomized 6061 and 5083 aluminum powders were ball milled in liquid nitrogen resulting in micron-sized powder containing 250-400 nm grains. Cold spray coatings prepared using these feed stock materials exhibited homogenous microstructures with grain sizes of 30-50 nm. TEM images of the as-received powders, ball-milled powders, and cold spray coatings are shown.     

等离子喷涂氧化铝陶瓷涂层研究现状及展望

简述了等离子喷涂制备常规氧化铝、Al2O3-TiO2、纳米氧化铝复合涂层及梯度涂层组织和性能的相关研究成果;简述了激光重熔技术和等离子喷涂技术复合制备涂层的研究现状;在粉末成分中加入低熔点缓冲相、稀土、碳纳米管等改善涂层微观组织,增强涂层功能,探讨基于氧化铝的特殊功能涂层,并对今后发展方向作了展望.     

悬浮液等离子喷涂热障涂层研究进展

悬浮液等离子喷涂(SPS)解决了纳米尺度粉末输送困难的问题,在热喷涂领域得到了快速发展。介绍了悬浮液等离子喷涂的原理和特点,综述了不同工艺条件对热障涂层结构的影响:降低弧电压的波动可以提高SPS工艺的可控性;降低喷枪功率、降低悬浮液浓度、增大喷涂距离,可实现涂层由垂直裂纹结构向柱状晶结构的演变;降低表面粗糙度可提高柱状晶的均匀性;溶剂为乙醇、溶质粒度分布合理的悬浮液更容易获得柱状晶结构。总结了SPS制备热障涂层产生垂直裂纹结构和类柱状晶结构的机理,认为在相同表面粗糙度下,熔滴尺寸和切向速度是影响涂层结构的关键。SPS-8YSZ涂层的隔热性能和热循环性能较好,具有良好的应用前景。     

铝合金表面超音速等离子喷涂WC-12Co涂层的结合机理

在经磨抛处理后的光滑铝合金表面上,利用超音速等离子喷涂制备WC-12Co涂层,通过扫描电镜观察分析,对涂层的结合机理进行了研究.发现涂层与基体的结合是以机械结合为主,还伴有部分冶金结合、物理结合和扩散.实验及模拟结果表明:硬质相WC能够嵌入到基体内部,基体的硬度越小,WC颗粒嵌入基体表面的深度越大;颗粒的速度越大,撞击基体产生的凹坑深度也越大.     

Development of Low-Oxide MCrAlY Coatings for Gas Turbine Applications

Advanced high-energy plasma systems are being used to achieve the benefits of the high-velocity oxy-fuel (HVOF) system without losing the inherent advantages of plasma for coating of gas turbine parts. MCrAlY coatings play a very important role in the performance and reliability of gas turbine components. One of the important considerations for next generation of gas turbines, which have more demanding conditions and need to withstand ever increasing operating temperatures, is that they should possess very low oxygen content levels in the coating. Low oxygen content coatings are applied by the expensive low-pressure plasma spray (LPPS)/vacuum plasma spray (VPS) technique for critical components in aero- and land-based gas turbines. This work deals with the development of low-cost LPPS equivalent coatings (having low oxygen content) using the high-energy high-velocity plasma spray (HEHVPS) gun and inert gas shroud. A comparison has also been made with CoNiCrAlY coatings by HVOF.     

Quantitative Topographical Characterization of Thermally Sprayed Coatings by Optical Microscopy

Topography measurements and roughness calculations for different rough surfaces (Rugotest surface comparator and thermally sprayed coatings) are presented. The surfaces are measured with a novel quantitative topography measurement technique based on optical stereomicroscopy and a comparison is made with established scanning stylus and optical profilometers. The results show that for most cases the different methods yield similar results. Stereomicroscopy is therefore a valuable method for topographical investigations in both quality control and research. On the other hand, the method based on optical microscopy demands a careful optimization of the experimental settings like the magnification and the illumination to achieve satisfactory results.     

大气等离子喷涂及固相反应法制备MnCoCu金属连接体防护涂层

目的 锰钴尖晶石涂层可有效抑制金属连接体高温氧化、降低固体氧化物燃料电池(SOFC)性能衰减,但其成本较高,电性能和稳定性也需进一步提升。方法 本文拟采用大气等离子喷涂技术(APS)和固相反应法以金属粉末制备高电导率尖晶石涂层。通过Cu元素的添加,在尖晶石涂层中引入高电导率的铜锰尖晶石相,获得高电导率尖晶石涂层,并通过对涂层的相组成、表面截面形貌、元素分布、电性能等物性的表征,揭示Cu添加量及固相转变条件对尖晶石涂层性能的影响规律。结果 800℃热处理后涂层明显致密化、均匀化,涂层主相为Cu_xMn_3-xO₄(x=1, 1.2, 1.4)和MnCo₂O₄;在基体和涂层的界面处存在Cr富集,800℃氧化10h后,含Cu量12%(质量分数)的试样面比电导最高;氧化100h后,面比电导有所下降,含Cu量12%(质量分数)试样仍具有最高的面比电导;经过还原的试样面比电导明显低于未还原样品,其原因在于还原过程中Cr元素产生扩散,氧化后生成了较多的低电导率相。涂层导电性随Cu含量的增加而增大...