Comparative investigation of microstructure and high-temperature oxidation resistance of high-velocity oxy-fuel sprayed CoNiCrAlY/nano-Al_(2)O_(3) composite coatings using satellited powders

Satellited CoNiCrAlY–Al_(2)O_(3)feedstocks with 2wt%, 4wt%, and 6wt% oxide nanoparticles and pure CoNiCrAlY powder were deposited by the high-velocity oxy fuel process on an Inconel738 superalloy substrate. The oxidation test was performed at 1050℃ for 5, 50, 100,150, 200, and 400 h. The microstructure and phase composition of powders and coatings were characterized by scanning electron microscopy and X-ray diffraction, respectively. The bonding strength of the coatings was also evaluated. The results proved that with the increase in the percentage of nanoparticles(from 2wt% to 6wt%), the amount of porosity(from 1vol% to 4.7vol%), unmelted particles, and roughness of the coatings(from 4.8 to 8.8 μm) increased, and the bonding strength decreased from 71 to 48 MPa. The thicknesses of the thermally grown oxide layer of pure and composite coatings(2wt%, 4wt%, and 6wt%) after 400 h oxidation were measured as 6.5, 5.5, 7.6, and 8.1 μm, respectively.The CoNiCrAlY–2wt% Al_(2)O_(3)coating showed the highest oxidation resistance due to the diffusion barrier effect of well-dispersed nanoparticles. The CoNiCrAlY–6wt% Al_(2)O_(3)coating had the lowest oxidation resistance due to its rough surface morphology and porous microstructure.

Enhanced high-temperature performance of Li-rich layered oxide via surface heterophase coating

Li-rich layered oxides have become one of the most concerned cathode materials for high-energy lithiumion batteries, but they still suffer from poor cycling stability and detrimental voltage decay, especially at elevated temperature. Herein, we proposed a surface heterophase coating engineering based on amorphous/crystalline Li3 PO4 to address these issues for Li-rich layered oxides via a facile wet chemical method. The heterophase coating layer combines the advantages of physical barrier effect achieved by amorphous Li3 PO4 with facilitated Li+diffusion stemmed from crystalline Li3 PO4. Consequently, the modified Li(1.2) Ni(0.2) Mn(0.6) O2 delivers higher initial coulombic efficiency of 92% with enhanced cycling stability at 55 °C(192.9 mAh/g after 100 cycles at 1 C). More importantly, the intrinsic voltage decay has been inhibited as well, i.e. the average potential drop per cycle decreases from 5.96 mV to 2.99 mV. This surface heterophase coating engineering provides an effective strategy to enhance the high-temperature electrochemical performances of Li-rich layered oxides and guides the direction of surface modification strategies for cathode materials in the future.

Microstructure studies of air-plasma-spray-deposited CoNiCrAlY coatings before and after thermal cyclic loading for high-temperature application

In the present study, bond-coats for thermal barrier coatings were deposited via air plasma spraying（APS） techniques onto Inconel 800 and Hastelloy C-276 alloy substrates. Scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, X-ray diffraction（XRD）, and atomic force microscopy（AFM） were used to investigate the phases and microstructure of the as-sprayed, APS-deposited Co Ni Cr Al Y bond-coatings. The aim of this work was to study the suitability of the bond-coat materials for high temperature applications. Confirmation of nanoscale grains of the γ/γ′-phase was obtained by TEM, high-resolution TEM, and AFM. We concluded that these changes result from the plastic deformation of the bond-coat during the deposition, resulting in Co Ni Cr Al Y bond-coatings with excellent thermal cyclic resistance suitable for use in high-temperature applications. Cyclic oxidative stability was observed to also depend on the underlying metallic alloy substrate.

High-Temperature Corrosion of Protective Coatings for Boiler Tubes in Thermal Power Plants

High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe corrosion occurs in molten salt corrosion environment. Materials rich in oxides formers, such as chromium and aluminum, are needed to resist corrosion in high-temperature and corrosive environment, but processability of such bulk alloys is very limited. High velocity electric arc spraying (HVAS) technology is adopted to produce coatings with high corrosion resistance. By comparison, NiCr (Ni-45Cr-4Ti) is recommended as a promising alloy coating for the water-wall tubes, which can even resist molten salt corrosion attack. In the study of corrosion mechanism, the modern material analysis methods, such as scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS), are used. It is found that the corrosion resistances of NiCr and FeCrAI coatings are much better than that of 20g steel, that the NiCr coatings have the best anti-corrosion properties, and that the NiCr coatings have slightly lower pores than FeCrAI coatings.It is testified that corrosion resistance of coatings is mainly determined by chromium content, and the microstructure of a coating is as important as the chemical composition of the material. In addition, the fracture mechanisms of coatings in the cycle of heating and cooling are put forward. The difference of the thermal physical properties between coatings and base metals results in the thermal stress inside the coatings. Consequently, the coatings spall from the base metal.

Ytterbium Hydroxide and Erbium Hydroxide Coating of Spherical Nickel Hydroxide Positive Materials for Ni-MH Batteries at High-Temperature

For the purpose of the important high-temperature charge-discharge performances of spherical Ni(OH)2 used as positive materials for Ni-MH batteries, Yb(OH)3 and Er(OH)3 were used for surface coating of spherical Ni(OH)2 to improve its high-temperature properties. The coated spherical Ni(OH)2 was prepared by chemically coprecipitation of Yb(OH)3 and Er(OH)3 on the surface of spherical Ni(OH)2, respectively. The products were characterized by X-ray diffraction(XRD) and scanning electron microscope(SEM). The X-ray analysis showed that the structure of the coated spherical Ni(OH)2 was still β-Ni(OH)2. The SEM studies revealed that coating layer uniformly covered the surface of spherical Ni(OH)2. The electrochemical studies revealed that coating of Yb(OH)3 and Er(OH)3 exhibited superior performance such as high discharge capacity, excellent charge-discharge properties at high-discharge rate at 65 ℃. The charge acceptance was above 85% at 1C rate at 65 ℃. The discharge capacity approached to 230 mAh·g-1 at 0.2C rate, which even reached 270 mAh·g-1 at 1C rate for both Yb(OH)3 and Er(OH)3 coated spherical Ni(OH)2, where the discharge capacity for uncoated one was only 250 mAh·g-1 . The cyclic voltammetry analysis of spherical Ni(OH)2 showed that the oxidation potential, the oxygen evolution potential, and the difference between them increased after the coating both at 25 and 65 ℃. It was shown that the Yb(OH)3 and Er(OH)3 coating is an effective way to improve the high-temperature performance of spherical Ni(OH)2 for Ni-MH batteries. The studies showed that Yb(OH)3 and Er(OH)3 coated spherical Ni(OH)2 would be a promising material of Ni-MH batteries for hybrid vehicle (HEVs), electric vehicles(EVs) and rapid charge devices due to excellent high rate charge-discharge performance.

Simple and scalable synthesis of super-repellent multilayer nanocomposite coating on Mg alloy with mechanochemical robustness,high-temperature endurance and electric protection

Multi-functionalization is the future development direction for protective coatings on metal surface,but has not yet been explored a lot.The effective integration of multiple functions into one material remains a huge challenge.Herein,a superhydrophobic multilayer coating integrated with multidimensional organic-inorganic components is designed on magnesium alloy via one-step plasma-induced thermal field assisted crosslinking deposition(PTCD)processing followed by after-thermal modification.Hard porous MgO ceramic layer and polytetrafluoroethylene(PTFE)nano-particles work as the bottom layer skeleton and filler components separately,forming an organic-inorganic multilayer structure,in which organic nano-particles can be crosslinked and cured to form a compact polymer-like outer layer with hierarchical surface textures.Remarkably,the chemical robustness after prolonged exposure to aqua regia,strong base and simulated seawater solution profits from polymer-like nanocomposite layer uniformly and compactly across the film bulk.Moreover,the self-similar multilayer structure coating endows it attractive functions of strong mechanical robustness(>100th cyclic rotary abrasion),stable and ultra-low friction coefficient(about 0.084),high-temperature endurance,and robust self-cleaning.The organic-inorganic multilayer coating also exhibits high insulating property with breakdown voltage of 1351.8±42.4 V,dielectric strength of 21.4±0.7 V/μm and resistivity of 3.2×10^(10)Ω·cm.The excellent multifunction benefits from ceramic bottom skeleton,the assembly and deposition of multidimensional nano-particles,and the synergistic effect of organic inorganic components.This study paves the way for designing next generation protective coating on magnesium alloy with great potential for multifunctional applications.

Highly oriented MXene/polyvinyl alcohol films prepared by scalable layer-by-layer blade coating for efficient electromagnetic interference shielding and infrared stealth

Controlling the orientation of two-dimensional MXene within layered films is essential to optimize or tune their mechanical properties and electromagnetic interference shielding(EMI)performance,but achieving the high orientation MXene layers on an industrial scale remains a challenging goal.In this paper,a scalable layer-by-layer blade coating(LbLBC)method was employed to fabricate highly oriented MXene/polyvinyl alcohol(PVA)films.During the LbLBC process,MXene/PVA colloid suffered a strong shearing effect,which induced the ordered alignment of MXene nanosheets along the direction of the blade movement.The orientation of MXene can be effectively adjusted by changing the scraping gap of LbLBC,achieving a maximum Herman orientation factor f of 0.81.As a result,the mechanical properties and EMI performance of the as-prepared MXene/PVA films are in direct proportion to their orientation,with the optimal values of tensile strength of 145.5 MPa,fracture strain of 19.6%,toughness of 17.7 MJ·m^(−3),and EMI shielding effectiveness of 36.7 dB.Furthermore,the inherently low mid-infrared(mid-IR)emissivity of MXene,combined with the densely oriented structure affords the composite films with IR stealth,resulting in a substantial decrease from 150 to 66.1℃in the radiative temperature of a surface.Conclusively,these scalable MXene/PVA films exhibit remarkable potential for integration into the next generation of multifunctional protective camouflage materials.

Microstructure and Oxidation Behaviors of Nano-particles Strengthened NiCoCrAlY Cladded Coatings on Superalloys

Nano-particles which can largely improve the microstructure and oxidation resistance of materials are often used as a strengthening component in metal matrix composites. However, few studies were reported on its application in the bond coat of duplex structure thermal barrier coating（TBC）. Three kinds of NiCoCrAlY coatings strengthened by different nano-particles with the same addition （1%, mass fraction） were prepared by the laser cladding technique on Ni-based superalloy substrates, aiming to study the effects of the nano-particles on microstructure and oxidation resistance of NiCoCrAlY coatings （the bond coat of the duplex structure thermal barrier coatings）. Scanning electron microscope （SEM）, X-ray diffractometer（XRD） and thermogravimetry were employed to investigate their morphologies, phases and cyclic oxidation behaviors in atmosphere at 1 050℃, compared with the coating without nano-particles. With the addition of nano-particles, the growth pattern of the grains at the interface changed from epitaxial growth to non-epitaxial growth or part-epitaxial growth; slender dendrites were broken and cellularized; cracks and pores were restrained; and the oxidation weight-gain and the stripping resistance of the oxide scale were improved as well. Among the three kinds of nano-particles, the SiC nano-particles showed the most improvement on microstructure, while the CeO2 nano-particles were insufficient, but its effects on the oxidation resistance are the same as those of the SiC nano-particles. Based on the discussions of the influence mechanism, it is believed that CeO2 nano-particles would show better improvement than SiC nano-particles if the proper amount is added and the proper preparation technique of micro-nanometer composite powders is adopted, with the synergistic action of nanometer effect and reactive element effect.

OXIDATION RESISTANCE OF NANOCRYSTAL ODS ALUMINIDE COATINGS PRODUCED BY PACK ALUMINIZING PROCESS ASSISTED BY BALL PEENING

Nanocrystal ODS （oxide dispersion strengthening） aluminide coatings were produced on a stainless steel and nickel-based superalloy by the pock aluminizing process assisted by ball peening, Pure Al powders and 1% of ultra-fine Y2O3 powders were mixed by ball milling. The ultra-fine Y2O3 powders were dispersed in Al particles. Ball peening welded the Al particles onto the substrate and accelerated the formation of aluminide coating. Nanocrystal ODS aluminide coatings were produced by the outward growth at a much low temperature （below 600℃） in a short treatment time. The effects of the operation temperature and treatment time on the formation of the coatings were analyzed. SEM （scanning electron microscope）, AFM （atomic force microscope）, EDS （energy dispersive X-ray spectroscopy）, XRF （X-ray fluorescence spectrometer） and XRD （X-ray diffraction） methods were applied to investigate the microstructure of the coatings. High-temperature oxidation tests were carried out to evaluate the oxidation resistance of the ODS aluminide coatings.

A New Process for Preparing Fine-ceramic-containing Composite Coatings──Flame Spray Synthesis

Flame spray synthesis (FSS), a combination of the flame spray technology and Self-propagation High-temperature Synthesis (SHS) was developed for preparing fine-ceramic-containing composite coatings. It can simplify the preparations of powder to synthesize and deposit the desired materials in one step. The preliminary results obtained from TiC-Fe cermet coatings by FSS process are reported. The peculiar microstructure of the composite coatings, which contains very fine (<1m) and round TiC and alternate TiC-rich (Hv=11€*13GPa) and TiC-poor layers (Hv=3.0 -6.0GPa), is expected to play an important role in their tribological properties.

Fe-Cr-Y_2O_3 MICRO-CRYSTALLINE COATINGS DEPOSITED BY SERIES ELECTRO-PULSE DISCHARGE

A new technique-series electro-pulse discharge (SEPD)-was developed as a sur-face coating process. In this technique, both positive and negative poles of a pulse power were used as the depositing electrodes with the substrate alloy as an induction electrode. Fe-Cr and Fe-Cr-Y2O3 micro-crystalline coatings were deposited on stain-less steel (Fe-18Cr-8Ni) surfaces. Oxidation at 950℃ in ambient air showed that the coatings greatly improved the oxidation resistance of the steel. The addition of dis-persed Y2O3 nano-particles into the alloy coatings was found to further reduce the scaling rate and enhance the adhesion of oxide scales.

Attenuation characteristics of electromagnetic waves in plasma generated by coating radionuclide on surface structures

Stealth technology plays an important role in modern military conflicts, especially when used in fighter jets. Since airfoil structures have a leading edge, inlet, and surface bulge that are easily detected by radar, it is necessary to study the stealth of these structures. In this study,we investigate structures coated with radionuclides to generate plasma. Using simulation and calculation methods, the attenuation of 0.1–10 GHz electromagnetic waves propagating in plasma was studied. The results showed that the attenuation of low-frequency electromagnetic waves is greater than that of high-frequency electromagnetic waves.The attenuation of 0.1–1 GHz electromagnetic waves is found to be less than-2.7 d B,-3.0 d B, and-15.6 d B at the airfoil leading edge, inlet, and surface bulge structures, respectively. We also found that the attenuation of electromagnetic waves with 0°-incidence is greater than that of waves with 10°, 20°, and 30° incidence angles.Additionally, the attenuation of electromagnetic waves decreases gradually as the incident angle increases.

Influence of Y_2O_3 on the Oxidation Behaviour of a β-NiAl Coating

A new-type of β-NiAl coating containing Y_2O_3 particles was obtained by electrolytic co-deposition and pack aluminizing techniques,and the influences of the nature of Y_2O_3 and its content on the oxidation behaviour of the coating at 1100℃ were studied.The test results indicate that the oxidation rates of the composite coatings are reduced and the scale adhesion is also improved remarkably.The content of Y_2O_3 has little influence on the oxidation rates of the composite coatings,but does obviously on the scale adhesion by modifying the configura- tion of the oxides at the scale-coating interface.The needle-like oxides penetrating into the coating show an obvious keying effect.A part of the dispersed Y_2O_3 in the as-deposited coating accumulates and forms a Y_2O_3-rich layer at the coating-substrate interface immediately after aluminizing.The layer is beneficial to reduce the degradation of the composite coating.

Colloidal Alumina-bonded TiB_2 Coating on Cathode Carbon Blocks in Aluminum Cells

Self-propagating high-temperature synthesis (SHS) with reduction process was used to fabricate TiB2 powder from TiO2-B2O3-Mg system. The colloidal alumina-bonded TiB2 paste was prepared and coated on the cathode carbon blocks. Various properties of the baked paste such as the corrosive resistance, thermal expansion and wettability were tested. Experimental results showed that the colloidal alumina-bonded TiB2 coating could be well wetted by liquid aluminum; and the thermal expansion coefficient of the coated material was 5.8x10(-6) degreesC(-1) at 20-1000 degreesC, which was close to that of the traditional anthracite block cathode (4x10(-6) degreesC(-1)); the electrical resistivity was 8 mu Omega (.)m at 900 degreesC when the content of alumina in the coated material was about 9% in mass fraction. In addition, some other good results such as sodium resistance were also reported.

先进航空发动机高温功能涂层研究进展

航空发动机是飞机的“心脏”。先进航空发动机正在向高推重比、高效率、低油耗和长寿命方向发展。以热障涂层、热/环境障复合涂层、高温隐身涂层等为代表的高温功能涂层应用于航空发动机关键热端部件,起着提升发动机服役性能、服役寿命和安全可靠性的重要作用。本文以热障涂层、热/环境障复合涂层、高温隐身涂层等为例,系统概述了近年来国内外以及北京航空航天大学在高温功能涂层材料设计、涂层制备科学与技术、涂层性能评价表征等方面的研究进展,并展望了先进航空发动机新型高温功能涂层所面临的挑战和发展动向。未来先进高温功能涂层的研究重点将集中在多功能复合涂层、极端环境适应性和工艺适配性等方面。

高温雷达吸波涂层研究进展

在现代信息化战争中,探测和制导技术迅猛发展。在众多探测信号中,雷达探测占比高达60%,因此武器装备雷达隐身能力尤其重要。随着新一代装备性能的提升,热端部件的服役温度不断升高,对高温雷达吸波涂层提出了更加严苛的要求。在高温服役环境下,部分雷达吸波材料存在氧化、居里温度低而失去吸波性能的问题。高温雷达吸波材料主要依靠介电损耗和电导损耗机制实现对电磁波的损耗吸收。基于此,综述了以碳化物、硼化物、氧化物、金属材料、MAX相材料为吸波剂的高温雷达吸波涂层研究情况,分析了各材料的优势及存在的问题,其中氧化物吸波剂高温稳定性好,易于制备,成本低,其吸波性能可通过掺杂改性调控,是面向未来更加严苛服役环境下更具应用潜力的吸波材料。此外,还从梯度结构和超材料设计2个角度分析了涂层结构设计在拓宽涂层吸波频带,降低涂层厚度方面的作用。结合当前研究进展提出了新材料研发、新结构设计和与材料结构相适应的制备工艺研究是未来高温雷达吸波涂层的发展方向。

吸波涂层应用方案自动寻优方法

在有限质量约束下实现宽频隐身性能最优,是隐身飞机吸波涂层应用方案设计所追求的目标。本文针对多种吸波涂层的最优化分区应用问题开展研究,建立了一套吸波涂层应用方案的自动优化方法。首先,基于时域有限差分法计算模型在不同频率、方位、极化下的电磁场,对各状态电磁场做归一化和加权计算后得到总电磁场。然后,将总电磁场按照特定方向、数量进行分区,并将每个分区分别赋予相应的吸波涂层,采用传输矩阵法计算吸波涂层的反射系数以将吸波涂层的影响叠加到电磁场中。对加载吸波涂层后的总电磁场进行近-远场变换,实现模型雷达散射截面(radar cross section,RCS)的快速计算。基于改进的单纯形法和Karush-Kuhn-Tucker条件建立自动优化方法,以降低RCS或减轻吸波涂层质量为目标函数,优化吸波涂层分区方案。最后,以行波板为例,开展包含3种厚度吸波涂层的应用方案减质优化。结果表明,优化方案相比1.5 mm厚吸波涂层方案可实现吸波涂层减重50%,且行波板RCS均值提高不超过1 dB,优化效果显著。

航空特种涂料的发展应用探讨

重点介绍了隐身涂料、耐高温涂料和抗静电涂料等航空特种涂料的国内外研制进展及应用情况,分析了特种涂料对航空维修的影响,为航空维修企业提供参考。

C/C复合材料表面低红外发射率薄膜研究

为降低C/C复合材料的红外发射率,同时提升其在高于400℃时的抗氧化性能,在C/C复合材料表面制备抗氧化涂层以提高其高温使用寿命。首先采用涂刷法在C/C复合材料表面制备SiC-玻璃复合抗氧化涂层,并在抗氧化涂层表面通过磁控溅射制备低红外发射率Ir薄膜。然后,系统探索并优化了抗氧化涂层和低红外发射率Ir薄膜的制备工艺,并探究了高温氧化行为对涂层红外发射率的影响。结果表明:固定溅射功率为100 W、溅射气压为1.2 Pa、靶基距为65 mm、基底温度为240℃时,在SiC-玻璃复合抗氧化涂层表面制备的低红外发射率Ir薄膜,在1 100℃下氧化1 h后,在3~5μm和8~14μm的红外发射率仍能保持0.1以下。

Study on the performance of lightweight roadway wall thermal insulation coating containing EP-GHB mixed ceramsite

As the mining depth increases,the problem of high-temperature thermal damage mainly caused by heat dissipation of surrounding rock is becoming more and more obvious.It is very important to solve the environmental problem of mine heat damage to improve the efficiency of mineral resource exploitation and protect the physical and mental health of workers.One can apply thermal insulation coating on the walls of mine roadways as a means of implementing active heat insulation.In this paper,expanded perlite(EP)and glazed hollow bead(GHB)are used as the main thermal insulation materials,ceramsite and sand as aggregate,plus glass fiber and sodium dodecyl sulfate to develop a new lightweight composite thermal insulation coating through orthogonal experiment method.According to the plate heat flow meter method and mechanical test method,the thermal insulation and mechanical properties of EP-GHB mixed ceramsite coating were studied by making specimens with different parameter ratios,and according to the analysis of the experimental results,the optimal mix ratio of the coating was selected.In addition,Fluent numerical simulation software was used to establish the roadway model,and the thermal insulation effect of the coating in the roadway under different working conditions was studied.The results show that the thermal conductivity of the prepared composite thermal insulation coating material is only 8.5% of that of ordinary cement mortar,and the optimal thickness of adding thermal insulation coating is 0.2 m,which can reduce the outlet air temperature of the roadway with a length of 1000 m by 4.87 K at this thickness.The thermal insulation coating developed in this study has the advantages of simple technology and strong practicability,and has certain popularization and application value in mine heat damage control.