等离子喷涂ZrC涂层耐烧蚀性能与机理研究

采用等离子喷涂工艺在C/SiC基体材料表面制备了较为致密的W粘结层和ZrC耐烧蚀涂层,利用氧乙炔火焰测试其抗烧蚀性能。结果表明:涂层具有良好的抗烧蚀性能。经烧蚀距离30 mm的氧乙炔烧蚀300 s后,涂层的质量烧蚀率为1.7×10~(-3)g·s~(-1),仅为无涂层试样的68%;线烧蚀率为4.0×10~(-4)mm·s~(-1),仅为无涂层试样的30%。随着烧蚀距离的减小,涂层的质量烧蚀率不断增大,线烧蚀率不断减小。试样表面温度梯度导致涂层存在3种典型烧蚀形貌,中心致密区,过渡区以及边缘疏松区。温度较高的中心区氧化产物为WO_3,其发生熔融并填充涂层内部孔隙和裂纹,形成致密层,且与ZrO_2所产生的协同效应有效降低了机械剥蚀几率,烧蚀以热化学烧蚀为主;温度较低的边缘区烧蚀产物未发生熔融且呈现疏松状,烧蚀主要表现为热化学烧蚀和机械剥蚀。     

固体火箭发动机3D C/C材料喉衬热结构模拟与烧蚀行为

以高氯酸铵/端羟基聚丁二烯/Al三组元为推进剂,在压强6.5 MPa、工作时间20、60、95 s的烧蚀条件下,进行长时间的固体火箭发动机烧蚀,模拟计算了喷管3D C/C材料喉衬热平衡状态下的对流换热系数、温度场和应力场,结合计算结果分析了喉衬各区的烧蚀特征与机理。结果表明：喉衬收敛段温度最高,烧蚀为氧化组分（H₂O、CO₂、H₂）与表面碳发生的热化学烧蚀;喉径区换热系数最大,温度较高,内表面在应力作用下,烧蚀最为严重,为燃气热化学烧蚀、高速气流机械剥蚀及粒子冲刷的共同作用,表面呈现出微小的沟槽或裂纹,应力与氧化使喉衬在低于材料极限应力下发生分解破坏;出口段应力降低,温度明显下降,烧蚀率显著降低。喉衬烧蚀机理为温度、应力影响下燃气氧化组分与碳的热化学烧蚀、气流机械剥蚀和Al₂O₃颗粒侵蚀的联合作用。     

TiB2-Cu-Ni梯度功能材料的抗烧蚀行为

采用燃烧合成与同时致密化技术制备了TiB2-Cu-Ni5层金属-陶瓷梯度功能材料。利用扫描电镜(SEM)、电子探针(EPMA)等方法对梯度材料的成分及烧蚀前后的微观组织形貌等进行了检测，用等离子火炬电弧加热器对材料进行加热来考察梯度材料的抗热震性能以及抗烧蚀性能。结果表明，梯度功能材料各层之间的界线已经模糊，层与层之间的结合较好；梯度材料在瞬间加热时和瞬间冷却时均未出现崩裂，烧蚀后表面没有裂纹产生，说明该梯度材料具有优异的抗热震性能；烧蚀20S后，梯度功能材料烧蚀后的质量损失仅为0．5g，说明梯度功能材料具有良好的抗烧蚀性能。梯度材料的抗烧蚀机理为金属粘接剂的挥发损失、热化学烧蚀和机械冲刷。该梯度材料在固体火箭发动机的喷管、喉衬等部件上有广阔的应用前景。     

高密度合金薄壁构件等离子喷涂成形技术

对喷雾造粒高密度合金粉末进行1 600℃瞬时烧结处理,采用常压氩气保护等离子喷涂成形技术制备了壁厚≤5 mm的零部件,研究真空固相及液相烧结对喷涂成形件显微结构、致密度及力学性能的影响。结果表明:瞬时液相烧结后,喷雾造粒团聚体内的微细球磨粉末由机械混合转变为冶金结合,喷涂沉积率从45%提高至70%以上。等离子喷涂沉积层为层片结构,致密度约88.9%。经1 200和1 300℃真空固相烧结后,沉积层保持原始的层片结构,成形件拉伸强度随致密度升高而增大,其断口呈典型的沿晶断裂形貌,伸长率为零。经1 400℃液相烧结后,成形件仍表现为层片结构及沿晶脆性断裂形貌。经1 465℃烧结后,沉积层由层片结构转变为颗粒结构,成形件致密度显著提高至98.05%;断裂方式以沿晶断裂为主,穿晶断裂为辅;拉伸强度显著增大至567.10 MPa,伸长率达8.65%。     

炭/炭复合材料耐烧蚀W涂层

采用等离子喷涂技术成功在坯体密度为1.8 g/cm~3炭/炭复合材料上面制备厚度为1.2 mm与基体结合良好的较致密的W涂层的试样。利用氧乙炔焰分别测试其在30 s、60 s、90 s和120 s下的烧蚀性能。结果表明:试样的质量烧蚀率和线烧蚀率均随时间的增加而增加。其中,最大质量烧蚀率和线烧蚀率分别为7.8μg/s和3.5μm/s。XRD、SEM分析表明:在烧蚀中心区,涂层试样的烧蚀以升华分解为主,同时,还伴有氧化烧蚀和微区机械剥蚀;在烧蚀过渡区,涂层的烧蚀机制以热氧化和燃气冲刷为主;而在烧蚀边缘区,涂层的烧蚀则主要表现为弱氧化烧蚀。     

扩散阴极用多孔钨基体材料的评述

本文梳理了扩散阴极对钨基体材料孔隙特性的设计要求。以其制备为主线,介绍了钨粉预处理、钨粉成形、钨压坯烧结、多孔钨渗（去）铜、钨骨架的热等静压及深冷加工;最后总结了钨基体材料的性能表征手段。阴极用钨粉等离子球化、挤压或注射成形是未来的发展趋势;钨骨架的热等静压改性有助于高可靠和长寿命;多孔钨的深冷加工是一种可持续的先进加工方法,有望实现钨基体的短流程制造。     

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.     

ZrCP/W复合材料的等离子烧蚀行为

采用等离子烧蚀装置对ZrCP/W复合材料的烧蚀性能进行了研究.结果表明:ZrCP/W复合材料的线烧蚀率随ZrC含量和烧蚀时间的增加而增大.烧蚀后,在试样表面形成了烧蚀坑和熔融层,熔融层的厚度达到1 mm左右.在烧蚀过程中,烧蚀层中的物相发生了化学反应,并生成了新相.复合材料的主要烧蚀机制是以熔化烧蚀为主,兼有热化学烧蚀.     

等离子喷涂W-TiC涂层的组织和性能研究

分别采用普通大气等离子喷涂和超音速大气等离子喷涂技术在低活化钢表面制备了添加1.5%TiC(质量分数)的钨基涂层。研究了涂层的组织和密度、氧含量、孔隙率和热导率等物理性能。结果表明,用两种工艺制备的涂层中,TiC主要分布于钨片层之间和未熔钨颗粒周围,对片层和颗粒起连接作用;与采用普通大气等离子喷涂制备的涂层相比,超音速大气等离子喷涂的W-TiC涂层的组织更加致密,氧含量降低了0.1%,孔隙率下降近一半,热导率提高至119.6 W/(mK)。     

NiCoCrAlY粘结层喷涂工艺对8YSZ热障涂层抗氧化性能的影响

目的 提高热障涂层粘结层的抗高温氧化性能。方法 分别采用爆炸喷涂和等离子喷涂工艺制备了不同结构的NiCoCrAlY粘结层,之后通过等离子喷涂制备8YSZ陶瓷层,分析了两种粘结层结构的热障涂层的抗高温氧化性能。利用XRD、SEM和EDS对涂层物相、微观结构和成分进行分析,并对其与基体结合状态、抗高温氧化性能进行研究。结果 爆炸喷涂粘结层内部组织致密,缺陷较少,与基体结合处孔隙少;而等离子喷涂粘结层内部的层状特征明显,孔隙较多,表面粗糙度较低。爆炸喷涂粘结层氧化5 h后,表面生成了一层富Al2O3的致密氧化物膜;而等离子喷涂粘结层表面形成了富NiO、CoO、Cr2O3和Ni(Cr,Al)2O4的氧化物层,并出现了许多微裂纹和片层状氧化物。爆炸喷涂制备的热障涂层试样在前5 h氧化增重速率高于等离子喷涂试样,随后变平缓,而等离子喷涂试样氧化速率依然较高。爆炸喷涂热障涂层的热生长氧化物层（Thermally grown oxide, TGO）经50 h氧化后,仍呈连续状,厚度均匀,粘结层内氧化物缺陷较少。结论 爆炸喷涂粘结层组织均匀、致密,喷涂时涂层的氧化以及热处理的内氧化较少,使得足够的Al较快速地在粘结层表面形成致密的氧化铝,表面一定厚度的氧化铝层抑制了氧和其他金属原子的相向扩散反应,提高了涂层的抗高温氧化性能。     

Elimination of porosity from aluminum-silicon castings by hot isostatic pressing

Specimens from two commercial aluminum-silicon casting alloys, with 0.060 and 0.100 maximum volume fractions of porosity, were hot isostatically pressed (HIPed) at 68.95 M Pa and various combinations of temperature (500 to 560 °C) and time (15 to 120 min). Optical microscopy and scanning electron microscopy (SEM) were used to document the distribution of porosity before and after HIPing in addition to standard stereological techniques and high-precision density measurements. It was found that HIPing these alloys for at least 120 min led to the elimination of porosity. In all cases, there was a significant increase in density after HIPing.     

A Novel Cu–GNPs Nanocomposite with Improved Thermal and Mechanical Properties

Classical powder metallurgy followed by either hot isostatic pressing(HIPing) or repressing–annealing process was used to produce Cu–graphene nanoplatelets(GNPs) nanocomposites in this work. A wet mixing method was used to disperse the graphene within the matrix. The results show that a uniform dispersion of GNPs at low graphene contents could be achieved, whereas agglomeration of graphene was revealed at higher graphene contents. Density evaluations showed that the relative density of pure copper and copper composites increased by using the post-processing techniques.However, it should be noticed that the efficiency of HIPing was remarkably higher than repressing–annealing process, and through the HIPing, fully dense samples were achieved. The Vickers hardness results showed that the reconsolidation steps can improve the mechanical strength of the specimens up to 50% owing to the progressive porosity elimination after reconsolidation. The thermal conductivity results of pure copper and composites at high temperatures showed that the postprocessing techniques could enhance the conductivity of materials significantly.     

Electro-deposition tangsten coating on low activation steel substrates from Na2WO4-ZnO-WO3 melt salt

Tungsten coating is considered as a promising alternative material for plasma facing materials(PFC)in future fusion devices.The electro-deposition of tungsten in Na2WO4-ZnO-WO3 melt at 1173 K on low activation steel substrates was studied in this work.Adherent and smooth tungsten films were deposited under various pulsed current conditions.The crystal structure and microstructure of tungsten deposits were characterized by XRD,SEM and EDX techniques.The results show that pulsed current density and duty cycle have a significant influence on tungsten nucleation and electro-crystallization phenomena.Uniform and smooth tungsten coating with high purity and high adherence is obtained on low active steel substrates as cathodic current density ranges from 35 to 25 mA·cm-2.     

镀液组成和工艺条件对电沉积钴钨合金成分的影响

研究了镀液中钨盐浓度，络合剂浓度，钠离子，电流密度，镀液温度等对电沉积钴钨合金成份的影响，结果表明：合金中的钨含量随钨盐浓度，电流密度和温度的升高而增大，随络合剂，钠离子浓度的升高而降低。     

Consolidation of nanocrystalline powders

Blended elemental Ti-24Al-11Nb (at.%) and Ti-55A1 (at.%) powders were mechanically alloyed and consolidated to full density by hot isostatic pressing (HIPing), Ceracon processing, and shock consolidation methods. Nanometer-sized grains were observed in all the samples, the finest size achieved in the shock-consolidated samples. The grain size was larger at higher HIPing temperatures. In comparison with conventional coarsegrained material, theHIP temperature for full consolidation could be brought down by about 400°C for the nanostructured titanium aluminides.     

Studies on the Mechanism,Structure and Microhardness of Ni-W Alloy Electrodeposits

The electrodeposition of Ni-W alloy has been studied on the glassy carbon electrode by the cyclic voltammetry and potentiostatic step methods. It has been found that electrodeposition of Ni-W alloy involves an intermediate valence tungsten oxide which inhibits hydrogen evolution. Ni-W alloy electrodeposition occurs by a mechanism involving progressive nucleation followed by three dimensional growth.

The structures of nickel-tungsten alloy deposits were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD results from Ni-W alloy deposits reveal a face-centered cubic solid solution, the microstructure of the deposits exhibit (111) preferred orientation. The lattice constant and microhardness of Ni-W alloy deposit increase as the tungsten content increases, the XPS results of Ni-W alloy deposits indicate that the nickel and tungsten of the deposits exist in the metallic state, but the Ni-W alloy deposit with a tungsten content of 40.7% is an intermetallic compound. The XPS results of the deposit with tungsten content of 40.7% show that the atomic ratio of Ni to W is 4:1, so β-Ni₄ W alloy can be obtained by electrodeposition and its microhardness (Hv) is as high as 672.8.     

靶材用钨铜复合材料的制备工艺

在真空条件下,采用高温烧结钨骨架后渗铜工艺制备靶材用钨铜复合材料,研究烧结温度对钨坯及钨铜复合材料组织与性能的影响.结果表明:随着烧结温度的提高,钨颗粒间逐渐由点接触扩大为面接触,烧结颈逐渐长大,同时孔隙不断缩小并趋于球形,钨骨架和钨铜复合材料相对密度及硬度不断增加,而钨铜复合材料的电导率不断下降.当烧结温度为1950 ℃时,钨骨架和钨铜复合材料的相对密度分别达到74.8%和96.9%的最高值;钨铜复合材料的硬度(HB)达最大值2520 MPa,而电导率则降低到36.6IACS%,其中氧含量仅为4×10-6,氮含量为3×10-6.     

Evaluation of plasma-sprayed tungsten for fusion reactors

Tungsten coatings are being considered for a variety of uses inside fusion reactors. Measurements of several properties of vacuum plasma- sprayed tungsten important for fusion energy applications are reported. Of vital concern is the thermal conductivity of the sprayed tungsten. Over the temperature range 25 to 1500 ‡, the thermal conductivity was approximately 60% of the value for high- purity tungsten. Of greater importance to reactor safety is the reactivity of tungsten with steam. It was found that the volatilization and reaction rates of plasma-sprayed tungsten from 800 to 1200 ‡ are similar to hot rolled tungsten. Several other useful properties have also been reported. The elastic constants of the sprayed tungsten were measured ultrasonically. The deposits were anisotropic; for example, the Young’s modulus measured in a direction parallel to the substrate was greater than that measured in the direction perpendicular to it, and their elastic moduli were approximately 30% lower than tabulated values for bulk tungsten. The average bulk density of the sprayed tungsten was approximately 17.4 g/cm , which is 90% of the theoretical density.     

Laser powder bed fusion of a pure tungsten ultra-fine single pinhole collimator for use in gamma ray detector characterisation

Laser Powder Bed Fusion is a leading additive manufacturing technology, whose use has been recently extended to refractory metals such as tungsten. This work was carried out to manufacture a pure tungsten pinhole collimator that would otherwise be difficult to produce using conventional methods such as machining. The laser powder bed fusion process was used to produce an ultra-fine 0.5 mm diameter hole running along a 40 mm long beam stop component. A laser powder bed fusion scanning strategy (laser energy density of 348 J/mm³) was selected with the aim of fabricating a high density tungsten component. The manufactured collimator was then used for gamma-ray detector characterisation. A collimated gamma-ray using a ²⁴¹Am source mounted on an automated scanning table was used to study the gamma-ray interaction with respect to position in a semiconductor detector, so that the position-dependent charge collection process could be characterized. The 0.5 mm diameter fine tungsten collimator yielded a relatively narrower beam spot, leading to more accurate scan results. However that was at the expense of number of gamma rays detected per second. Overall, the 0.5 mm collimator allowed for higher resolution scans giving better detector characterisation results in comparison to a 1 mm diameter collimator.