Removal and repair techniques for thermal barrier coatings: a review

ABSTRACT

A comprehensive literature review of the existing techniques for removing and repairing of damaged thermal barrier coatings is presented, with the focus on top ceramic coats. The advantages and disadvantages of each technique are compared and assessed. The review shows that there is not a universal method applicable to all coating systems. The selection of the coating removal and repair process must be specific to damaged coating systems, based on their composition, type of damages, and available resources. This review will provide some inside look at various approaches in an effort to meet the different coating repair needs.     

Research on corrosion performance of 6061 aluminum alloy in salt spray environment

Salt spray corrosion test was carried out on 6061 aluminum alloy, and quasi-static tensile test at room temperature was carried out on the sample with universal testing machine. The effect of salt spray corrosion on the mechanical properties of 6061 aluminum alloy was studied by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and electrochemistry. The corrosion rate of 6061 aluminum alloy was quantitatively characterized by different corrosion parameters. It was found that local corrosion of 6061 aluminum alloy occurred in salt spray environment, mainly pitting corrosion and intergranular corrosion. With the increase of corrosion time, the polarization resistance of 6061 aluminum alloy decreases, and the corrosion rate significantly increases. The average corrosion rate and the maximum corrosion rate of 6061 aluminum alloy were characterized by corrosion weight loss and corrosion pit depth. And they can be transformed into each other. The mechanical properties of 6061 aluminum alloy were mainly affected by the depth of corrosion pit. With the increase of corrosion time, the tensile strength and fracture strain decreased, resulting in poor plasticity of the sample. At the same time, the change of elongation of 6061 aluminum alloy can be accurately predicted by the depth of corrosion pit.     

等离子喷涂与脉冲等离子爆炸复合涂层的氧化组织分析

采用等离子喷涂在镍基高温合金GH4049表面制备了CoNiCrAlY涂层,随后对涂层进行了脉冲等离子爆炸和真空预氧化处理,并对涂层进行了1050℃保温10 h和50 h的恒温静态氧化实验。结果表明:经过脉冲等离子爆炸处理后的涂层表面形貌更加平坦,脉冲等离子爆炸处理使得涂层表面的片层结构转变为致密结构,减少了氧气渗入涂层的通道,有效延缓了涂层的氧化过程,且没有改变涂层的化学成分;在1050℃空气中氧化50 h后,涂层的物相组成与未氧化处理的基本一致。     

Fatigue strength and microstructure evaluation of Al 7050 alloy wires recycled by spray forming,extrusion and rotary swaging

Recycled high-strength aluminum alloys have limited use as structural materials due to poor mechanical properties. Spray forming remelting followed by hot extrusion is a promising route for reprocessing 7xxx alloys. The 7050 alloy machining chips were spray formed, hot extruded, rotary swaged and heat-treated in order to improve mechanical properties. Microstructures, tensile properties and fatigue strength results for a 2.7 mm-diameter recycled wire are presented. Secondary phases and precipitates were investigated by XRD, SEM, EBSD, TEM and DSC. As-swaged and heat-treated (solution and aging) conditions were evaluated. Mechanical properties of both conditions outperformed AA7050 aerospace specification. Substantial grain refinement resulted from the extensive plastic deformation imposed by rotary swaging. Refined micrometric and sub-micrometric Al grains, as well as coarse and fine intermetallic precipitates were observed. Subsequent solution treatment resulted in a homogeneous, recrystallized and equiaxed microstructure with grain size of 9 μm. Nanoscale GP(I) zones and η′ phase precipitates formed after aging at 120 °C, imparting higher tensile (586 MPa) and fatigue (198 MPa) strengths.     

Spray-dry synthesis of β-Cu1.8Zn0.2V2O7 ceramic fine particles showing giant negative thermal expansion

We used spray-dry method to synthesize fine powder of β-Cu_1.8Zn_0.2V₂O₇ showing large negative thermal expansion (NTE) linearly to temperature over a wide temperature range. The NTE of β-Cu_1.8Zn_0.2V₂O₇ is produced by microstructures consisting of voids and anisotropic thermal deformation of crystal grains in ceramics. By reducing the size of the microstructures that produce NTE, large NTE equivalent to that of bulk was realized, even for ceramic particles of about 2 μm size. Comparison with particles produced using a conventional method demonstrates that the particle size distribution is narrow and that the particles are nearly spherical. This achievement is expected to pave the way to use of NTE materials in micrometer-scale control of thermal expansion.     

喷涂缠绕保温管用全水发泡聚氨酯组合聚醚的研制

用聚醚多元醇A、聚醚二醇B、聚酯多元醇PS-2915、三乙醇胺、水和其他助剂制备了喷涂管道用全水发泡聚氨酯硬泡组合聚醚,并对其反应性能、黏度进行评价,对使用该组合聚醚和多异氰酸酯PM-200制得的聚氨酯泡沫材料的性能进行研究。结果表明,在合适的原料用量时,制得的组合聚醚黏度较低,与多异氰酸酯PM-200的反应速度满足喷涂管道生产工艺要求。当喷涂制得的聚氨酯泡沫单层厚度7 mm左右,泡沫体具有较高的粘接强度、较好的韧性和较低的导热系数,密度61 kg/m^3的泡沫压缩强度达到526 kPa。制得的喷涂管道产品满足GB/T 34611—2017要求。     

快干羟基丙烯酸酯乳液的合成及性能研究

采用核壳乳液聚合方法制备了羟值为 1.5%的低羟丙烯酸酯乳液。研究了聚合物理论 T_g、壳中羟基质量分数、核聚合物 Hansch参数对双组分漆膜干燥速度的影响。结果表明：漆膜干燥速度随理论 T_g、壳中羟基质量分数及核聚合物 Hansch参数的增加而加快，当 T_g为 50 ℃、壳中羟基质量分数为 1.1%、核聚合物 Hansch参数为 3.43时，漆膜于 25 ℃、60%相对湿度下的实干时间可缩短至 95 min，在大巴、工程机械涂装等需要快干的领域具备潜在应用价值。     

Microstructures,mechanical properties and corrosion resistance of sprayed Ca–P coating for micropatterning carbon/carbon substrate surface

Carbon/carbon (C/C) surface micropatterning is a method of modifying the surface into the complete and regular geometry. In this work, we introduce a positive effect on bonding strength between sprayed Ca–P coating and surface micropatterning C/C substrate. Interestingly, C/C substrate coated by Ca–P coating provides textured surface for a new bone ingrowth. The sprayed Ca–P coating is then subjected to microwave-hydrothermal (MH) treatment with the aim of eliminating surface defects and obtaining a uniform purity phase. These objectives were achieved in our previous study by the MH method. The molar ratio of Ca/P in the coatings is nearly close to 1, which is far below that of Ca/P for hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HA, 1.67). The purpose of this article is to transform the phases in the sprayed Ca–P coating, which owns the better bioactivity and high corrosion resistance. In order to raise the molar ratio of Ca/P, the coatings are treated under high-temperature (around 700 °C). They are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and a fourier transform infrared spectra (FTIR). The bonding strength (coating/substrate), biological activity and corrosion resistance of the coatings are investigated. The resulting coatings own the different microstructures and phase compositions from the original sprayed Ca–P coating. Especially, results show that the shear strength of the sprayed Ca–P coating deposited on surface micropatterning C/C substrate increases by 61% which is more than that of the coating on non-surface micropatterning C/C substrate. Additionally, high-temperature treated coating presents a good biological activity and an excellent corrosion resistance of current density (1.3078 × 10^-6 A/cm²) and potential (−0.17 V_SCE).     

Retention of Eucalyptol,a Natural Volatile Insecticide,in Delivery Systems Based on Hydroxypropyl‐β‐Cyclodextrin and Liposomes

Eucalyptol (Euc) is a natural monoterpene with insecticide effects. Being highly volatile and sensitive to ambient conditions, its encapsulation would enlarge its application. Euc‐loaded conventional liposomes (CL), cyclodextrin/drug inclusion complex, and drug‐in‐cyclodextrin‐in‐liposomes (DCL) are prepared to protect Euc from degradation, reduce its evaporation, and provide its controlled release. The liposomal suspension is freeze‐dried using hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) as cryoprotectant. The liposomes are characterized before and after freeze‐drying. The effect of Euc on the fluidity of liposomal membrane is also examined. A release study of Euc from delivery systems, in powder and reconstituted forms, is performed by multiple head extraction at 60 °C after 6 months of storage at 4 °C. CL and DCL suspensions are homogeneous, show nanometric vesicles size, spherical shape, and negative surface charge before and after freeze‐drying. Moreover, HP‐β‐CD does not affect the fluidity of liposomes. CL formulations present a weak encapsulation for Euc. The loading capacity of eucalyptol in DCL is 38 times higher than that in CL formulation. In addition, freeze‐dried DCL and HP‐β‐CD/Euc inclusion complex show a higher retention of eucalyptol than CL delivery system. Both carrier systems HP‐β‐CD/Euc and Euc‐loaded DCL decrease Euc evaporation and improve its retention. Practical Applications: Eucalyptol is a natural insecticide. It is highly volatile and poorly soluble in water. To enlarge its application, its encapsulation in three delivery systems (conventional liposomes, cyclodextrin/drug inclusion complex, combined system composed of cyclodextrin inclusion complex and liposome) is studied. In this paper it is proved that cyclodextrin/eucalyptol inclusion complex and eucalyptol‐in‐cyclodextrin‐in‐liposome are effective delivery systems for encalyptol encapsulation, retention, and release.     

冷喷涂固态颗粒沉积中颗粒间结合形成机制研究进展

就目前主流的冷喷涂颗粒结合形成机理进行了系统总结和评述,为冷喷涂沉积体性能的调控和后续研究提供借鉴。分别就经典的颗粒界面绝热剪切失稳结合机理,颗粒界面应力波释放诱导材料射流形成结合机理,以及高速碰撞诱导颗粒表面氧化膜破碎、新鲜金属接触结合机理的基本概念、原理、特点进行了概括总结。通过大量系统文献的调研,指出现有理论目前存在的相悖和不足之处,并简要分析了现有颗粒间结合形成理论对冷喷涂沉积体质量调控方面的指导意义。最后基于现有研究的不足,对冷喷涂颗粒界面结合机制方面的研究进行了展望。