Thermal control materials are the key materials to ensure the space orbit operation of spacecraft,among which La0.8Sr0.2MnO3 ceramics with good radiation characteristics have been widely investigated.With the rapid development of aerospace technology,the radiation regulation ability of thermal control materials was required for multi-functional intelligent spacecraft.In this paper,La0.8Sr0.2MnO3 thermal control ceramic coating was prepared by atmospheric plasma spraying technique.The influence of coating porosity and substrate type in the hemispherical emissivity of La0.8Sr0.2MnO3 coating was studied through the regulation of spraying parameters,and the related mechanism was explored.It provides a certain research basis for the atmospheric plasma sprayed coatings with excellent radiation properties for thermal control applications.
Aluminum bronze polyester composite powder was prepared by agglomeration composite process,and aluminum bronze polyester coating was prepared by atmospheric plasma spraying process,and an isothermal oxidation experiment was conducted at 600℃for 1000 h to characterize the phase structure,microstructure,porosity,high-temperature hardness,and friction and wear performance of the coating.The results show that the distribution of polyester and pores in the sprayed coating is uniform.The phase composition of the coating is mainly α and β'Phase,the coating exhibits excellent antioxidant performance.The higher the porosity,the lower the hardness.After 2 minutes of wear,it basically reached a stable wear stage.The friction coefficient of the coating was between 0.8 and 1.1 after oxidation for 5 to 100 hours,and the volumetric wear rate was between 0.00116 and 0.00199 mm 3·N-1·m-1.The friction coefficients of the coatings after oxidation for 500 h and 1000 h are 1.0 and 0.7 respectively,and the volumetric wear rates are 8.42×10-4 mm3·N-1·m-1 and 7.78×10-4 mm3·N-1·m-1,the oxide film under long-term oxidation plays a role in reducing wear and lubrication.The wear mechanism of the coating after oxidation for 5 to 100 hours is abrasive wear and fatigue wear.The wear mechanisms of coatings oxidized for 500 h and 1000 h are abrasive wear,oxidation wear,and fatigue wear.
The abradable sealing coating is an important way to improve the air tightness and efficiency of aviation engines,and the coating structure has a significant impact on its thermal stress and service life.In this study,AlSi/PHB sealing coating was used as the research object,and the finite element model of the coating with different structural parameters were established using ABAQUS finite element simulation software and Python programming language.The effects of top-layer thickness,PHB particle and pore structures on the thermal stress of the coating under thermal shock conditions were systematically studied.The results show that when the top-layer thickness is from 0.1mm to 1.9mm,the effect of the thickness on the stress at the coating-substrate interface is less than that on the stress at the side of the coating.When the top-layer thickness exceeds about 0.3 mm,the part of the coating where the maximum tensile stress occurs changes from the coating-substrate interface to the side of the coating.When the content of PHB particles is 30 to 50 vol.%,the peak stresses at the coating-substrate interface and the side of the coating do not fluctuate significantly with the increase of PHB particle content.When the porosity of the top layer is 5 to 15 vol.%,the peak stress at the coating-substrate interface decreases first and then increases with the increase of the porosity.When the pore diameter is 60 μm to 110 μm,the peak stress at the coating interior increases as the pore diameter increases.Comprehensive considering the relationship between thermal stress and coating structure,the optimal structural parameters for the AlSi/PHB sealing coating are as follows:the top-layer thickness should be in the range of 0.3 mm to 1.1 mm,the content of PHB particles should be in the range of 40 vol.%to 50 vol.%,and the porosity of the top layer should be about 11 vol.%,the pore diameter of the surface layer is between 70 μm and 80 μm.
Labyrinth is a kind of sealing structure in aero-engine.In order to achieve better wearing resistance,preparing the protective coating on tip surface is needed.In China,plasma-sprayed alumina-based wear-resistant coatings are commonly used,but they tend to delaminate and provide inadequate protection under harsh conditions.In recent years,a new type of cutting coating prepared by composite electrodeposition process emerges internationally,with superior performance.Nickel-cubic boron nitride(Ni-cBN)is a typical coating of this new coating technology.In this study,Ni-cBN cutting coating was prepared using a composite electrodeposition process on FGH95 substrate samples and shape simulation parts.The cutting performance of the coating after cutting GH3536 metal honeycomb under high-temperature and high-speed conditions were investigated.The results show that Ni-cBN cutting coating can cut well-defined grooves on the metal honeycomb,reduce the temperature rise during cutting by about 80℃,keep cutting performance after heat treatment,and exhibit excellent active cutting performance without signs of overheating or burn marks.
Laser drilling is an important method for cooling holes in superalloys with thermal barrier coatings.In this paper,fully stabilized tetragonal phase thermal barrier coatings were prepared using spherical thin-walled hollow shell fully stabilized nano t'-YSZ powders,and the thermal barrier coatings were subjected to film hole processing using a femtosecond laser.The results show that the holes prepared by femtosecond laser are regular with no recast and shrinkage.There was no cracking at each interface in the coating,indicating that the coating maintained a good bond during processing.The distribution of elemental compositions in the superalloys was not affected by laser drilling,indicating that the alloy substrate material maintained good chemical stability.After the thermal barrier coating was quenched at 1050℃for 100 times,the shape of the air film holes remained intact and the coating did not peel off.It indicates that the t'-YSZ coatings with processed film holes have high thermal shock resistance.
Thermally sprayed ceramic insulating coatings are widely applied to provide workpiece insulation due to their excellent dielectric and mechanical properties.The dielectric performance is determined by the coating materials and preparation techniques.Firstly,the dielectric and mechanical property characteristics of several ceramic materials,including high-purity Al2O3,doped Al2O3(doping MgO,TiO2,or ZrO2),and other materials(Y2O3,MgAl2O4),were summarized.Among these,as the most widely used coating material,high-purity Al2O3 has great dielectric strength and volume resistivity and its purity,phase compositions and defect orientations have a significant impact on the dielectric properties of coatings.However,high-purity Al2O3 coating has poor impact resistance and high preparation cost,and we can dope the Mg or Ti element in Al2O3 to reduce the powder melting temperature and improve the coating's deposition efficiency and density.Moreover,mixing partial-stabilized tetragonal ZrO2 in Al2O3 can also improve the impact toughness with the mechanism of phase transformation toughening.Doping and mixing other elements in Al2O3 will damage the dielectric property more and less,but enhance the comprehensive performance.Furthermore,Y2O3 can be used for insulating protection in ion etching environments and MgAl2O4 is appropriate for some harsh service environments due to its excellent dielectric and mechanical performances.Secondly,the effect on coating microstructure of different thermal spraying methods(including plasma spraying,high-velocity oxygen fuel spraying and detonation gas spraying)was analyzed and it was found that powder characteristics and spraying parameters(such as spraying power、particle flight speed and flame atmosphere)have a significant impact on the porosity,crack density and phase composition of the coating,which further affect the dielectric properties.Pores and cracks would seriously damage the dielectric properties of coatings,but they can be filled with the sealing process in which different sealers,sealing techniques and the physical and chemical characteristics of high-performance sealers were introduced.Additionally,heating treatment above transition temperature allows the metastable phase to transform to the high dielectric stable phase.Thirdly,the dielectric breakdown,resistivity,polarization,and environmental adaptability of insulating coatings were described.The dielectric breakdown strength is related to the electrode structure,voltage rise mode,and environment humidity and the test data can be processed by Weibull Distribution.Constantly reinforced partial discharging caused the dielectric breakdown.The three-electrode method was adapted to avoid the interference of stray currents in the insulation resistance testing.And the coating has an obvious"absorbing electrical charge"phenomenon due to its multi-hierarchies and abundant grain boundaries.At low-frequency voltage,space charge polarization is the main polarization manner of the ceramic insulating coatings,in which conductivity and polarization loss both exist.In a high-humidity environment,adsorbed water on the pore and crack surface will significantly reduce the resistivity and increase the dielectric constant.At last,the future research directions of thermally sprayed ceramic insulating coatings were proposed based on the true service environment.
WC-Co coating has been gradually applied to the surface protection of rolls.At present,a large number of experiments have been conducted to prepare WC-Co coating by thermal spraying,laser cladding and surfacing welding.In this paper,the high-velocity oxygen fuel spray(HVOF)is used to prepare WC-Co coating on the surface of Q235 steel,and the NiCr transition layer is added between the WC-Co coating and the substrate.The testing methods are adopted by SEM,XRD,friction and wear testing,fatigue and wear testing,etc.The morphology,structure and properties of the coating were compared with those of the coating without transition layer.After adding NiCr transition layer,the hardness of WC-12Co+NiCr and WC-10Co-4Cr+NiCr coatings are 1059.64 HV0.3 and 1016.96 HV0.3,respectively.There are higher than WC-12Co(960.01 HV0.3)and WC-10Co-4Cr coatings(1012.20 HV0.3).The wear rate of WC-12Co+NiCr coating(5.19×10-15 m3·(N·m)-1)is much lower than that of WC-12Co coating(6.59×10-15 m3·(N·m)-1).The wear volume of WC-12Co coating in fatigue wear is reduced from 2644.58×10-12 m3 to 1193.20×10-12 m3 of WC-12Co+NiCr coating.
The Ni-5%Al/Al2O3-TiO2 wear-resistant sealing coating prepared by plasma spraying process is widely used in the labyrinth seal system of aeroengine.The coating thickness plays a crucial role in improving the efficiency of the engine.As the labyrinth seal clearance decreases from 1.0 mm to 0.2 mm,the actual gas leakage rate decreases by 73%.The shape of the labyrinth parts is complex,and the batch production control involves many aspects such as human-machine material ring measurement.This paper mainly discusses the coating thickness and appearance control in batch production.The sealing grate avoids the local accumulation of the coating and eliminates the burrs and other defects at the boundary of the coating by using silicone rubber and metal tools to protect it.In this paper,by establishing the corresponding relationship between the coating thickness between the test piece and the grate and the comparison relationship between different measurement methods,the indirect control of the coating on the grate parts in the process of batch production is realized which makes effective nondestructive testing of coating thickness realized.
Fe-based amorphous material maintains supreme wear and corrosion resistance,and the preparation of Fe-based amorphous coatings via High Velocity Air Fuel Spraying(HVAF,air/propane)technology has attracted considerable attention in recent years.Due to the very high velocity of the melted Fe-based amorphous powder,it is easy to cause gun blockage,which limits the engineering application of this technology.In this research,10 wt.%～20 wt.%white corundum sand with a size of 180-mesh was added into the Fe-based amorphous powder to improve the spray stability of the coating.The effects of white corundum sand content,spraying gas pressure,powder feeding rate,and the stand-off distance on the deposition efficiency,tensile bonding strength,porosity rate of the coating,and the gun blockage condition were studied.Results show that composite powder composed of Fe-based powder and white corundum sand are helpful to achieve stable spraying for more than 20 min.The as-sprayed coating has a bonding strength of more than 40 MPa,porosity of less than 1%,and a significant improvement in gun blockage.HVAF process method suitable for spraying of Fe-based amorphous powder has been optimized in this paper,which can guide the promotion and application of this technology.
TiC reinforced Duplex stainless steel composite coating was prepared on 40 CrNiMo matrix by laser cladding technology.The phase composition of the coating mainly includes austenite,martensite,M7C3 carbides and TiC.Among them,M7C3 type carbides mainly contain Fe7C3,Cr7C3 or(Fe,Cr)7C3,TiC includes micron level TiC precipitated after melting and coarse unmelted TiC particles.The precipitated TiC particles were square-shaped and grew petal-like with the increase of TiC addition.The unmelted TiC particles form a diffusion interface with the substrate,and have good interface bonding.When adding 30 wt.%TiC,the cladding layer has the best wear resistance,its hardness can reach 55.26 HRC,wear volume is 2.54×10-2 mm3,wear resistance is 3.37 times that of substrate.
Lithium batteries have many advantages such as high energy density,long lifespan,lightweight,and environmental protection,making them a modern and efficient energy storage technology.The preparation process of positive electrode materials for lithium batteries requires a sagger as a container for high-temperature sintering treatment,which may cause cracking,peeling,and other failure phenomena during use.Improving the high-temperature resistance,corrosion resistance,and adhesion resistance of the saggar can effectively increase its service life,greatly reduce production costs,and ensure product quality.This study selected alumina(Al2O3)as the coating material and prepared a uniform and dense coating on the inner surface of the saggar(mullite cordierite)using plasma thermal spraying technology.The material was sintered at high temperature and the protective performance of the coating was studied and analyzed.After 50 sintering tests(950℃,12h),the sagger coating showed no obvious peeling or detachment.During the sintering process,a corrosion product layer is formed on the surface of the saggar coating,while the rest of the coating is still a dense alumina coating,effectively preventing material corrosion of the saggar.Among them,lithium battery materials only adhere slightly to the corrosion layer cracks of the sagger coating,and the coating has excellent anti adhesion effect.
采用等离子喷涂工艺制备了铜铝聚苯酯封严涂层,完成了 96 h中性盐雾试验、72 h酸性大气试验、24 d周期浸润试验以及 450℃、线速度 300 m/s、进给速率 5～480 μm/s的高温高速可磨耗试验,研究了涂层的耐蚀性能和可磨耗性能.结果表明:铜铝聚苯酯封严涂层在 72h酸性大气腐蚀后,涂层表面光滑平整,未观察到腐蚀产物和点蚀坑;24 d周期的浸润腐蚀后,涂层颜色未发生明显改变,涂层表面结构完整,未观察到腐蚀产物和点蚀坑;96 h中性盐雾腐蚀后,涂层表面未观察到腐蚀坑,但涂层表面出现大片褐色斑块;不同进给速率下,叶片进给深度比IDR值不大于9.79%;检测及分析结果表明,涂层拥有优异的耐腐蚀性能和可磨耗性能.
TaC涂层在还原气氛下能耐酸、碱、盐等物质的腐蚀,是优异的表面防护涂层材料.本文结合喷雾干燥与等离子球化技术制备TaC粉体,并采用真空等离子喷涂技术制备TaC涂层.采用真空碳管炉对涂层进行渗碳处理,比较研究不同渗碳温度对涂层结构和物相组成的影响.结果发现,相较于喷雾造粒,等离子球化处理的TaC粉体呈致密球形,该粉体制备的涂层较为致密,孔隙率较低.此外,喷涂过程中TaC发生脱碳产生Ta2C相,而渗碳反应可以将喷涂过程中产生的Ta2C相转化成TaC相.Ta2C与C反应生成TaC的过程受动力学控制,当渗碳温度超过900℃时,几乎完全转化为TaC相.
针对普通喷砂枪"能量利用率较低,喷砂效率特低"的现状,引入了引射式暂冲型风洞扩压喷气嘴的多孔结构和Laval喷管完全膨胀状态设计理念,设计了风洞式喷砂枪.多孔结构缩短了混合距离,是缩小版的风洞扩压喷气嘴,喷砂管之内大部分区域是超声速气流,因而提高了引射效率.进一步地,由于风洞式喷砂枪内部仍残存有亚声速区域,喷砂效率仍未达到压入式喷砂机的水平应与此问题有一定关联性.在风洞喷砂技术的基础上设计了诱导式喷砂枪,以压力诱导方式在喷砂管内部气流全部实现了超声速(超声速气流全域化),为砂粒加速创造更加有利的条件;力图打造一款喷砂效率效果赶超压入式喷砂机,且仍然轻便适用的喷砂枪.本文通过CFD数值模拟喷砂枪内部的流体参数分布说明诱导式喷砂枪改造的新颖性和合理性.
为解决钛合金表面直接进行电镀涂层制备结合力较低的问题,本文采用超音速火焰喷涂技术在钛合金叶尖表面制备了不同厚度NiCoCrAlY底层,并在底层表面用复合电镀技术制备了Ni-cBN耐磨面层.研究表明NiCoCrAlY-Ni-cBN耐磨涂层的组织结构良好,结合强度大于 74.2 MPa,能够在 600℃大气环境中长时间保持组织和结构稳定.NiCoCrAlY-Ni-cBN钛合金叶尖涂层与NiCrFe/Al/hBN封严涂层的对磨匹配效果良好,可以为钛合金叶尖提供良好的对磨防护.
CuAl合金是重要的可磨耗封严涂层骨架材料,Al含量会对涂层的性能产生显著影响.为了明确不同Al含量对可磨耗封严涂层的热性能产生的影响,文章采用基于密度泛函理论的第一性原理方法,使用特殊准随机结构对Al含量从0至18.750at.%的α相的铜铝二元合金进行了建模,并结合准谐近似方法研究了其弹性常数、熔点、热膨胀系数、比热容等性质.利用真空感应熔炼法制备了Al名义含量为11.0at.%、15.0 at.%、18.9 at.%三组不同组分的铜铝合金,对其熔点、热膨胀系数与比热容进行了实验表征.计算结果表明,随着Al含量的增加,CuAl无序固溶体的熔点呈下降趋势,CuAl合金的热膨胀系数呈升高趋势,CuAl合金的定压比热容先升高后降低,计算值与实验测量值符合良好.本工作可以为铜铝合金涂层成分设计提供一定理论与实验数据参考.
采用超音速火焰喷涂技术(HVOF)在F92阀芯材料表面制备NiCr-Cr3C2 单层和NiCr+NiCr-Cr3C2 双层涂层.通过扫描电镜(SEM)、X射线衍射仪(XRD)、维氏硬度计、高温摩擦试验机等探究了两类涂层的显微形貌、相结构、力学及高温摩擦学性能.结果表明:两种涂层成分均匀、结构致密.其中,单层涂层的表面硬度较低(810.19±22.74 HV),且摩擦系数范围由低温的0.4～0.9到高温的0.3～0.7,磨损率从3.19×10-6 mm3/(N•m)到3.06×10-5 mm3/(N•m),单层涂层在高温下(630℃)表现出更为优异的耐磨性能;双层涂层具有较高的表面硬度(869.68±44.12 HV),且摩擦系数受摩擦往复频率影响在0.4～0.8波动,磨损率维持在2.5×10-5 mm3/(N•m)左右,受磨损频率因素影响较小,更能适用于频率频繁变换(1 Hz～5 Hz)的服役环境中.C析出生成的Cr7C3 与高温氧化生成的Cr2O3 之间的协同作用能够提高涂层的高温摩擦磨损性能,磨损机理分析表明:两种涂层的高温摩擦磨损形式相似,整个磨损过程由磨粒磨损、黏着磨损构成.
随着先进航空发动机推进引擎向着高推动力和长服役寿命的方向发展,如今传统的含有6-8 wt%的氧化钇稳定氧化锆(6-8YSZ)热障涂层材料体系,在服役温度 1200℃以上时,YSZ陶瓷涂层会发生高温相变,产生涂层间的热应力,最终导致涂层剥落失效,因此新材料体系的引入和涂层结构的改进刻不容缓.本文介绍了传统YSZ的发展历史并且阐述了掺杂稀土氧化物稳定氧化锆、钙钛矿结构和稀土锆酸盐(A2Zr2O7)即烧绿石结构等陶瓷材料体系的研究进展和发展前景,并分析了新型氧化铪基体陶瓷热障涂层体系和高熵材料体系涂层研究现状和未来发展趋势,最后对新型热障涂层材料的问题和发展进行了总结和展望.
等离子喷涂-物理气相沉积(PS-PVD)工艺由于具有非视线沉积效果,在加工复杂型面和多联体导向叶片表面热障涂层具有高均匀性的优势而被广泛关注.为了进一步研究PS-PVD高能、高速射流的非视线沉积效果,验证固定直径圆柱挡杆(Φ22 mm)不同距离遮蔽对平面沉积样品沉积行为的影响.结果表明:无遮蔽条件下,基体表面涂层厚度分布呈中部厚而四周薄,呈现高斯峰分布特征,涂层最大厚度为 135 μm;有遮挡条件下,涂层厚度呈现双峰的结构特征,在 15 mm的遮挡距离时,遮挡区域基体沉积的涂层最薄,其他遮挡距离下,涂层厚度在0～40 μm之间变化.对遮蔽区域位置涂层显微形貌进行分析,发现不同位置的遮蔽区域正后方,气相的速率和浓度明显降低,导致柱状结构生长时形成气相沉积为主的结构,同时扩散速率较低导致气相生长较慢;在遮蔽区域的边缘,由于遮蔽效应,涂层中的冷凝颗粒明显增多;遮蔽区域涂层厚度明显降低,且挡杆距基体距离越远,遮蔽区域的厚度分布越不规则,受射流的扰动影响越大.
热障涂层中陶瓷层界面处的应力应变场对其破坏起到至关重要的作用,但之前的研究并未考虑热障涂层宏观构型与细观界面的交互影响.本文建立了在轴向和周向具有不同波长的 3D涂层界面有限元模型,分析了轴向波长和周向波长对涂层界面应力的影响规律,获得了轴向波长和周向波长对涂层界面应力综合影响的关系式.研究结果表明,减小轴向波长会增大涂层界面破坏的风险,增大周向波长能够同时减小周向和轴向的最大应力,有利于降低涂层界面破坏的风险;轴向波长为0.051 mm,周向波长为0.030 mm时,周向最大应力最小,为243.1 MPa;周向波长和轴向波长均大于0.03 mm时,周向与轴向应力差值小于40 MPa,界面应力分布的均匀性较好.本文研究为涂层制备时的界面优化设计提供了理论基础.
