铜基体上等离子体喷涂钨涂层性能研究

介绍了铜基体上等离子喷涂1 mm钨涂层核聚变试验装置壁材料的制备,并对真空和大气等离子体喷涂钨涂层性能进行了比较研究,内容主要包括微观形貌、气孔率、杂质含量、结合强度和热负荷性能.结果表明,气孔率和氧杂质含量差异是大气和真空等离子体喷涂钨涂层热负荷性能差异的主要原因.     

大气与真空等离子体喷涂钨涂层的比较

利用等离子体喷涂技术在铜合金基体上制备1mm的钨涂层,并对大气和真空等离子体喷涂钨涂层性能进行比较。结果表明,真空喷涂钨涂层气孔率低、传热能力高、杂质含量低、结合强度高,热负荷性能好。与大气等离子体喷涂钨涂层相比,真空喷涂技术更适合应用到核聚变实验装置内壁上。     

铜基体上爆炸喷涂钨涂层及其电子束热负荷实验研究

详细介绍了爆炸喷涂法在铜基体上制备钨涂层.磁约束核聚变面对等离子体材料要求有承受较高热负荷的性能,电子束辐照热负荷实验发现:0.3 mm的钨涂层可以承受5.13 MW/m2的热通量;在2 MW/m2、20s脉冲的条件下,样品能承受300周的疲劳而没出现破裂现象,且距离表面5 mm处铜基体的温度在70°C左右;5 MW/m2、2 s脉冲的条件下,样品可承受95周热疲劳,且距离表面5 mm处铜基体的温度不高于200°C.钨铜的热膨胀系数和杨氏模量相差很大,在加载热通量过程中,界面处产生应力,这将影响材料的耐热冲击性能,但爆炸喷涂仍然为制备核聚变较低热通量区域面对等离子体材料的一种参考方法.     

钨涂层面对等离子体材料损伤演变行为研究

利用等离子体喷涂技术制备了钨涂层面对等离子体材料,并对涂层基本性能进行了表征,主要包括气孔率,相对密度,结合强度,热导率,硬度分布,进而研究主动水冷钨涂层在热负荷服役条件下损伤演变行为。研究发现,直接水冷钨涂层内部层与层之间的开裂、分层是涂层失效的原因,损伤演变过程为柱状晶体再结晶并长大、层间微裂纹出现、裂纹扩展和气孔出现、最后材料分层、失效。间接水冷钨材料的热负荷性能受到很大限制,且疲劳性能降低,失效形式是涂层开裂或脱落,甚至铜基体整体熔化。     

钨涂层面对等离子体材料损伤演变行为

利用等离子体喷涂技术制备了钨涂层面对等离子体材料,并对涂层基本性能进行了表征,主要包括气孔率、相对密度、结合强度、热导率、硬度分布,进而研究主动水冷钨涂层在热负荷服役条件下的损伤演变行为。研究发现,直接水冷钨涂层内部层与层之间的开裂、分层是涂层失效的原因,损伤演变过程为柱状晶体再结晶并长大、层间微裂纹出现、裂纹扩展和气孔出现、最后材料分层、失效。间接水冷钨材料的热负荷性能受到很大限制,且疲劳性能降低,失效形式是涂层开裂或脱落,甚至铜基体整体熔化。     

Thermal Performance and Microstructure of Vacuum Plasma Sprayed Tungsten Coatings under Cyclic Heat Load

采用真空等离子喷涂技术在铜基体表面制备了钨涂层,分别通过NiCrAl和W75Cu25涂层作为中间层。5 MW/m2, 2 s的高热负荷电子束实验表明NiCrAl中间层提高了涂层的热导率并降低了热应力和残余应力值。W75Cu25涂层作为中间层则表现出较差的热疲劳性能。高热负荷电子束真空等离子喷涂钨涂层表现出侵蚀和微裂纹。因热应力导致涂层发生塑性变形,在高温情况下裂纹起源于熔融的钨颗粒,但是,裂纹被钨涂层塑性变形和孔洞所抑制     

真空等离子喷涂钨涂层组织与热行为研究（英文）

采用真空等离子喷涂技术在铜基体表面制备了钨涂层,分别通过NiCrAl和W75Cu25涂层作为中间层。5 MW/m2,2 s的高热负荷电子束实验表明NiCrAl中间层提高了涂层的热导率并降低了热应力和残余应力值。W75Cu25涂层作为中间层则表现出较差的热疲劳性能。高热负荷电子束真空等离子喷涂钨涂层表现出侵蚀和微裂纹。因热应力导致涂层发生塑性变形,在高温情况下裂纹起源于熔融的钨颗粒,但是,裂纹被钨涂层塑性变形和孔洞所抑制。     

钨涂层等离子体喷涂参数优化分析

利用等离子体喷涂技术在铜基体上制备1 mm厚的钨涂层,并分析了不同喷涂功率及Ar/H2条件对涂层微观形貌、气孔率、热导率、表面粗糙度及成分等的影响。结果显示,喷涂功率对涂层性能影响较大,Ar/H2比值大小也会影响钨粒子飞行速度和粒子熔化状态,进而影响涂层性能。在功率大于40 k W、Ar/H2=35/15时钨粒子熔化状态较好,涂层表面粗糙度较小,涂层气孔率较小,传热性能较好。     

VPS-EBW法制备W／Cu功能梯度材料及热负荷实验研究

采用真空等离子体喷涂-电子束焊接法制备出核聚变面对等离子体W／Cu功能梯度材料，梯度材料中成分分布均匀、密度较高。电子束辐照热负荷实验发现：8MW／m^2的热负荷条件下，样品可以承受20s的辐照：在2．5Mw／m^2，4．5MW／m^2，6MW／m^2的热负荷条件下，样品可分别承受26s，22s，20s的辐照而没有出现明显的损伤现象。样品疲劳实验也表现出很好的性能：8MW／m^2，10s辐照，可以承受70周热疲劳：6MW／m^2，20s辐照，在第90周裂纹开始形成；在2．5MW／m^2，辐照时间为30s和4．5MW／m^2，辐照时间为25s条件下，样品经过100周热疲劳实验均没有出现明显的损伤现象。对已出现裂纹的断面作X射线能量色散能谱（EDS）分析发现，由于焊料本身或者焊接时引入的杂质和虚焊，导致材料承受较高热负荷实验时的热应力迅速增大到破裂极限，使表面温度快速升高，而导致材料连接失效。     

面向等离子体材料钨厚涂层的制备及表征

等离子体喷涂技术在面向等离子体材料钨涂层的制备中占据主导地位,本实验采用CuMo/MoW作为涂层的中间过渡层,分别以结晶钨粉和羰基钨粉为原料,用大气等离子体喷涂技术在CuCrZr合金基体(110 mm×130mm)上制备了3-4 mm厚的3种钨涂层.对钨涂层微观组织、力学性能和热学性能研究表明,羰基钨粉制备的钨涂层的综合性能优于结晶钨粉,且薄涂层的结合强度优于厚涂层.优化喷涂工艺后,金相法测得钨涂层孔隙率＜2％,涂层的结合强度最大值为10 MPa,EDS测得氧含量为6％左右,纯钨层热导率最大值为12.52 W/(m.K),涂层氧含量过高导致涂层热导率显著降低.研究表明采用大气等离子体喷涂技术在铜合金上制备3～4mm厚的钨涂层是可行的,该技术可为下一步低成本、高性能厚钨涂层的制备奠定基础.     

Surface damage during transient thermal load of 50% thickness reduced W-2% (Vol.) Y2O3 sheet with different recrystallization volume fraction

Thermal shock damage of tungsten as a plasma facing material (PFM) depends on thermal shock power density level, duration and repeated time, and microstructure of the sample. The recrystallization process will degrade the mechanical property of material and thus change the its thermal shock resistance. The effects of recrystallization volume fraction on thermal shock response of W-Y₂O₃ under different power density levels (0.22–0.44 GW/m²) has been systematically studied. Electron beam pulse of duration of 1 ms with 100 recycles was used to simulate the transient thermal load of fusion device. The changes of morphology, distance, depth, width of crack and surface roughness on the rolling direction-normal direction (RD-ND) surfaces of W-Y₂O₃ samples with different recrystallization volume fraction were investigated. The results showed that recrystallization process have significant influence on the thermal shock resistance of W-Y₂O₃ samples. For the rolled sample, crack depth, width and surface roughness increased with the increased of power density level while crack distance decreased. The partially and fully recrystallized samples showed significant wider crack networks and severe surface modification.     

Substitution of ThO2 by La2O3 additions in tungsten electrodes for atmospheric plasma spraying

ThO₂ additions are commonly used in tungsten-based electrodes for plasma spraying due to the excellent electron emissivity, improved arcing behavior, higher strength, and better machinability. Because of their radioactive potential, which makes handling, use, recycling, and disposal more difficult, alternative additives are required that provide the same advantages as thoriated tungsten, but without environmental hazards. Within this work, tungsten cathodes with 2 wt.% ThO₂ and 1 wt.% La₂O₃ were compared with respect to their arc ignition behavior, plasma stability and arc erosion. Both, cyclic and continuous plasma spraying experiments were carried out. In addition, structure and mechanical properties of Al₂O₃ coatings sprayed on Mo substrates were evaluated. La₂O₃ is characterized by a similar plasma ignition and operation behavior as well as a comparable coating quality with respect to ThO₂ additions. Further, La₂O₃ additions caused a reduced degradation of the cathode material, which is attributed to the lower cathode temperature, giving rise to an expected longer lifetime.     

Preparation and Thermophysical Properties of La2Zr2O7 Coatings by Thermal Spraying of an Amorphous Precursor

Free-standing La₂Zr₂O₇ coatings were obtained by plasma spraying, using an amorphous La-O-Zr precursor as the feedstock. The La-O-Zr precursor powder was prepared by coprecipitation. During thermal spraying, the formation of coatings can be regarded as a joint process of melting-solidification, thermal decomposition, and crystallization. The time required for crystal growth was significantly shortened during spraying. Consequently, the average grain size of coatings was approximately 200 nm, with a narrow distribution (100-500 nm). Coatings prepared by this method show better thermophysical properties than those prepared with crystalline La₂Zr₂O₇ powder as the feedstock. The thermal conductivity of the as-sprayed coating was approximately 0.36-0.47 W/m K and the average coefficient of thermal expansion (CTE) is 11.1 × 10^?6/K.     

Effect of Oxidation Behavior on the Mechanical and Thermal Properties of Plasma Sprayed Tungsten Coatings

Tungsten (W) coatings have been prepared via air (APS) and vacuum plasma spraying (VPS) technologies, respectively. The microstructures and chemical compositions of the coatings were comparatively studied; meanwhile, the mechanical and thermal properties were evaluated. The results obtained showed that oxide content in the VPS-W coating was apparently lower than that of the APS-W coating because of the different surrounding atmosphere, which influenced the mechanical and thermal properties of the coatings directly. Similar microstructures were observed for the VPS-W and the APS-W coating, but the VPS-W coating was much denser. The bonding strength of the VPS-W coating was much higher than that of the APS-W coating. Thermal conductivity of the VPS-W coating was 59.3 W/m · K at room temperature while the APS-W coating was 32.2 W/m  K. Thermal loading experiments of electron beam showed that the VPS-W coating could withstand the heat load of 10.75 MW/m², while the APS-W coating formed serious cracks on its surface at the load of 7.5 MW/m².     

Direct production of porous cathode material (La1−x Sr x MnO3) using a reactive DC thermal plasma spray system

The cathode material (La_0.8Sr_0.2MnO₃) in solid oxide fuel cells (SOFCs) was plasma sprayed on mild steel in a reactive DC thermal plasma spray process. This high-speed process of depositing thin films for the components of SOFCs was examined experimentally. The results showed that a coating layer of La_0.8Sr_0.2MnO₃ with a particular porosity could be obtained directly using both prereacted La_0.8Sr_0.2MnO₃ and mixed raw materials (La₂O₃, SrCO₃, and MnO or MnCO₃) as feed materials with or without a pore former. The heat treatment of the plasma coating material at 1073 K (800 °C) for 3 h significantly enhanced the desired crystallization of La_0.8Sr_0.2MnO₃ in the coated material.     

SPS烧结W-TaC的耐瞬态热冲击性能

通过高能球磨方法制备了系列W-TaC混合粉末,采用放电等离子体烧结(SPS)制备出弥散强化W-TaC样品,并对W-TaC样品的密度、硬度和微观组织进行了分析。利用60 k W电子束材料测试平台(EMS-60)对烧结W-TaC的耐瞬态热冲击性能进行测试,分别模拟了等离子体破裂和边缘局域模2种热负荷。实验后通过扫描电镜观察了样品加载区域的裂纹及熔化情况,通过透射电镜观察分析了材料的微结构特征。结果表明:W-TaC样品在热负荷作用下可以经受功率密度为740 MW/m~2、5 ms的热冲击而不产生裂纹,但在功率密度为550 MW/m~2、100次1 ms的热疲劳下会产生疲劳微裂纹。SEM和TEM分析表明,TaC颗粒在钨晶粒内和晶粒间都有存在,而且TaC会与W形成共格相界和半共格晶界从而增强钨合金的强度。     

Thermo-Physical Properties and Thermal Shock Resistance of Segmented La2Ce2O7/YSZ Thermal Barrier Coatings

La₂Ce₂O₇ (LCO)/yttria-stabilized zirconia (YSZ) thermal barrier coating (TBC) with segmentation crack structure was produced by atmospheric plasma spraying. Thermo-physical properties, such as thermal diffusivities and thermal conductivities, and thermal cycling performance of the segmented LCO/YSZ TBC were investigated. The thermal conductivity of the segmented coating was measured to be around 1.02 W/mK at 1200 °C, relatively lower than that of the non-segmented coating, respectively. The segmented LCO/YSZ TBC exhibited a thermal cycling lifetime of around 2100 cycles, improving the durability by nearly 50% as compared to the non-segmented TBC. The failure of the segmented coating occurred by chipping spallation and delamination cracking within the coating.