Chemical synthesis and sintering behaviour of highly dispersed W/Cu composite powders

The paper reports the preparation of W/Cu composite powders by a wet process based on the reduction of selected copper precursors in ethylene glycol and in the presence of tungsten powders. Reactions were performed in different conditions of temperature, time and concentration of the copper precursor. Two different Cu compounds, Cu(AcO)₂·H₂O and CuO (coarse or fine) and two W powders (coarse or fine) were used. The reaction yields ranged from 75% to 98%. Dense bodies (up to 97% fractional density) with highly homogeneous microstructure as well as high electrical conductivity (up to 41% IACS) were obtained by sintering W/Cu powders at 1350 °C.     

Hierarchically porous ceramics via direct writing of preceramic polymer-triblock copolymer inks

Hierarchically porous ceramics possess tailored porosity across multiple length scales, giving rise to materials with low density, high specific properties, and multifunctionality. Here, we report a method that combines self-assembly and 3D printing to create ceramic architectures with hierarchical porosity spanning from the nano- to microscale. To programmably define their microscale porosity, an additive manufacturing method, known as direct ink writing, is used to create 3D lattices composed of cylindrical struts. Nanoscale porosity is generated within each strut by block copolymer templating followed by photopolymerization and pyrolysis in a non-oxidative environment, which transforms the preceramic polymer, polycarbosilane, into silicon oxycarbide with a “nanocoral” morphology. The resulting hierarchically porous ceramic lattices exhibit excellent mechanical energy absorption (0.31 MJ/m³), comparable to metal alloy foams. They also possess an order of magnitude lower thermal conductivity (0.087–0.16 W/m⋅K) compared to bulk preceramic polymer-derived ceramics. Prior to pyrolysis, the printed architectures can be manipulated to produce more complex shapes, including lattices with twisted, helical, and overhang features as well as repeated folding to create an origami airplane. By combining self- and directed assembly, our approach opens new avenues for creating hierarchically porous ceramics.     

Mechanical milling to foster the solid solution formation and densification in Cr-W-Si for hot-pressing of PVD target materials

Based on the significantly different melting points and high oxygen affinities, the fabrication of chromium-based tungsten silicides is restricted to powder metallurgical production routes. To foster particle contacts and diffusion processes between chromium and tungsten, which are known to necessitate long sintering times, mechanical alloying or milling processes prior to sintering are established. Nonetheless, due to spinodal decomposition of Cr and W, the solid solution formation is complex and yet little understood. For this reason, the influence of the mechanical milling time (0–24 h) on the crystal structure and the microstructural properties of hot-pressed 60Cr30W10Si (wt.–%) is examined. In this context, two different powders containing a different tungsten particle size (0.8 and 3 µm) were mechanically alloyed to analyze the impact on the phase formation and the particle distribution in the microstructure. It was shown that mechanical milling supported the mechanical clamping between the particles. However, the increased milling times significantly decreased the crystallite sizes of the particles and fostered the tungsten solubility in the Cr-rich (Cr, W) solid solution formed during sintering, thus supporting the densification.     

Investigation on preparation and mechanical properties of W–Cu–Zn alloy with low W–W contiguity and high ductility

In order to improve the mechanical properties of the W–Cu alloy, the W–Cu–Zn alloys with low W–W contiguity were fabricated by three different preparation methods. For the first method, the mixed powder of copper-coated tungsten powder and Zn powder was sintered by SPS (Spark Plasma Sintering) process. For the second method, the mixed powder was processed by CIP (Cold Isostatic Pressing) before SPS. For the third method, a skeleton of the copper-coated tungsten powder was prepared by CIP, and then the skeleton was infiltrated with H70 brass. The microstructure, mechanical properties and failure mechanism of the prepared W–Cu–Zn alloys were investigated. The results show that the W–Cu–Zn alloy fabricated by the third method achieves a high relative density of 98.4% and a low W–W contiguity of 10%. The alloy exhibits a high dynamic compressive strength of 1000 MPa, with a high critical failure strain of 0.7. The Cu-Zn matrix of the alloy fabricated by the third method is composed of α-phase Cu–Zn alloy and Cu₃Zn particles. The homogeneous distribution of Zn in the matrix manifests good solution strengthening effect and the uniformly distributed Cu₃Zn particles has a strong precipitation strengthening effect, which are both responsible for the evidently enhanced mechanical properties.     

激光燃烧合成掺杂钨精矿FeAl复合材料组织及性能

通过对掺杂不同含量钨精矿粉末Fe-Al系粉末压坯进行激光点燃自蔓延烧结(SHS), 利用XRD、 SEM、 硬度测试、 磨损测试表征手段, 分析研究了钨精矿粉含量对烧结合金微观组织结构及宏观性能的影响。实验结果表明: 在烧结过程中, 压坯实现了自蔓延燃烧。合金组织为针状组织, 且随着钨精矿粉含量的增加, 针状组织长大。产物物相主要为AlFe、 AlFe₃、 WO₃以及Fe₇W₆。当钨精矿粉添加量为1%时, 烧结合金显微硬度最大, 达到HK956, 烧结合金的密度最大, 为4.27 g/cm³, 孔隙率最小, 为12.2%, 烧结合金的相对磨损率最低, 达到0.05%。     

采用定向SiC纳米线烧结制备高强多孔 SiC陶瓷

利用直接墨水打印方法制备了由定向SiC纳米线交错叠层组成的具备网络状孔隙结构的高强SiC多孔陶瓷.制备的碳化硅多孔陶瓷具有高的通孔结构和完全由定向SiC纳米线组装而成的结构特征.研究了烧结温度对定向SiC纳米线多孔陶瓷的微观结构、相组成演变及力学性能的影响.研究结果表明:烧结温度低于1900℃时,SiC纳米线能保持高长...     

Sintering of nanostructured W-Cu alloys prepared by mechanical alloying

Nanostructured (NS) powders with compositions corresponding to W-20wt%Cu and W-30wt%Cu were prepared by mechanical alloying. The microstructure and grain size of as-milled and annealed powders were analyzed by transmission electron microscopy. The compacted specimens were sintered at temperatures in the range 1000 °–1300 °, and then the microstructures of sintered parts were analyzed by scanning electron microscopy. Sintering of mechanically alloyed W-Cu alloys appears to be independent of Cu content, and may be explained in terms of recovery and grain growth in the mechanically alloyed powders as well as impurity activated sintering of W. After sintering, Cu pools are formed outside the mechanically alloyed powders. A relative sintered density of more than 95% is obtained by particle rearrangement during liquid-phase sintering, and the greatest homogeneity of W and Cu phases is achieved by sintering at 1200 °.     

Free‐Standing Polyurethane Nanofiber/Nets Air Filters for Effective PM Capture

The filtration performance and light transmittance of nanofiber air filters are restricted by their thick fiber diameter, large pore size, and substrate dependence, which can be solved by constructing substrate‐free fibrous membranes with true nanoscale diameters and ultrathin thicknesses, however, it has proven to be extremely challenging. Herein, a roust approach is presented to create free‐standing polyurethane (PU) nanofiber/nets air filters composed of bonded nanofibers and 2D nanonets for particular matter (PM) capture via combining electrospinning/netting technique and facile peel off process from designed substrates. This strategy causes widely distributed Steiner‐tree structured nanonets with diameters of ≈20 nm and bonded scaffold nanofibers to assemble into ultrathin membranes with small pore size, high porosity, and robust mechanical strength on a large scale based on ionic liquid inspiration and surface structure optimization of receiver substrates. As a consequence, the resulting free‐standing PU nanofiber/nets filters exhibit high PM_1–0.5 removal efficiency of >99.00% and PM_2.5–1 removal efficiency of >99.73%, maintaining high light transmittance of ≈70% and low pressure drop of 28 Pa; even achieve >99.97% removal efficiency with ≈40% transmittance for PM_0.3 filtration, and robust purification capacity for real smoke PM_2.5, making them promising high‐efficiency and transparent filtration materials for various filtration and separation applications.     

Inkjet‐Printed High‐Q Nanocrystalline Diamond Resonators

Diamond is a highly desirable material for state‐of‐the‐art micro‐electromechanical (MEMS) devices, radio‐frequency filters and mass sensors, due to its extreme properties and robustness. However, the fabrication/integration of diamond structures into Si‐based components remain costly and complex. In this work, a lithography‐free, low‐cost method is introduced to fabricate diamond‐based micro‐resonators: a modified home/office desktop inkjet printer is used to locally deposit nanodiamond ink as ?50–60 µm spots, which are grown into ≈1 µm thick nanocrystalline diamond film disks by chemical vapor deposition, and suspended by reactive ion etching. The frequency response of the fabricated structures is analyzed by laser interferometry, showing resonance frequencies in the range of ≈9–30 MHz, with Q ‐factors exceeding 10⁴, and (f₀ × Q) figure of merit up to ≈2.5 × 10¹¹ Hz in vacuum. Analysis in controlled atmospheres shows a clear dependence of the Q‐factors on gas pressure up until 1 atm, with Q ∝ 1/P. When applied as mass sensors, the inkjet‐printed diamond resonators yield mass responsivities up to 981 Hz fg^?1 after Au deposition, and ultrahigh mass resolution up to 278 ± 48 zg, thus outperforming many similar devices produced by traditional top‐down, lithography‐based techniques. In summary, this work demonstrates the fabrication of functional high‐performance diamond‐based micro‐sensors by direct inkjet printing.     

Thermal conductivity of Cu/diamond composites prepared by a new pretreatment of diamond powder

Cu/diamond composites were fabricated by spark plasma sintering (SPS) after the surface pretreatment of the diamond powders, in which the diamond particles were mixed with copper powder and tungsten powder (carbide forming element W). The effects of the pretreatment temperature and the diamond particle size on the thermal conductivity of diamond/copper composites were investigated. It was found that when 300 μm diamond particles and Cu–5 wt.% W were mixed and preheated at 1313 K, the composites has a relatively higher density and its thermal conductivity approaches 672 W (m K)⁻¹.     

Densification,microstructure, and properties of W-Mo-Cu alloys prepared with nano-sized Cu powders via large electric current sintering

This study rapidly fabricated a novel W-Mo-Cu alloy by large current electric field sintering at a relatively low temperature, and the effects of the powder size of Cu on the densification, microstructure, and properties were comprehensively investigated. The particle size of Cu did not influence the phase type but significantly affected the densification, microstructure, and properties. XRD and TEM results showed that the alloy contained three new phases aside from W, Mo, and Cu phases, i.e., Mo-W ordered phase, Mo-Cu solid solution, and Cu_0.4W_0.6 intermetallic compound. Copper powders with smaller sizes were beneficial to improving the distributional homogeneity of elements and the sintering densification. Therefore, the alloy prepared with 100 nm Cu powders had a denser and more homogeneous microstructure and better comprehensive properties than that prepared with 5 μm Cu powders. Overall, the W-Mo-Cu alloy prepared with 100 nm Cu powders at 980 °C proposed the best comprehensive properties, and its relative density can reach 98% approximately.     

Macroporous SiOC Ceramics with Dense Struts by Positive Sponge Replication Technique

Highly porous SiOC ceramics (≥90% open porosity) containing dense struts have been prepared following positive sponge replication technique using silsesquioxane based preceramic polymer. The morphological features including cell size, cell window size, and strut size of the macroporous SiOC ceramics have been analyzed using electron microscopy. Subtle variation in the crosslinking condition of the preceramic polymer infiltrated polyurethane template enables the formation of hollow as well as dense struts, which has a profound influence on compressive strength of the macroporous bodies. Synchrotron radiation micro computed tomography is used to construct the three dimensional images of the macroporous ceramics that indicate isotropy of the pores and excellent interconnectivity.

     

Microstructure and Ablation Behavior of W Coating Prepared by Atmospheric Plasma Spraying for Zr/Cu Infiltrated C/C Composites

To improve the ablation resistance of carbon/carbon (C/C) composites, W coating prepared by atmospheric plasma spraying (APS) for Zr/Cu infiltrated C/C composites are fabricated, the Zr/Cu infiltrated C/C composites are prepared by reactive melt infiltration (RMI). The microstructural features of the composites are examined by scanning electron microscopy coupled with energy dispersive spectrometry (SEM‐EDS), X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The ablation resistance of the W coated Zr/Cu infiltrated composites are tested in the oxyacetylene torch environment at heat flux of 4186 kW m^?2 for 150 s. The results show that the diameter of ablation center and line ablation rate (LAR) of W coated composites are about 3.92 mm and 5.16 × 10^?3 mm s^?1. Compared to pure C/C and the Zr/Cu infiltrated composites, the diameters of ablation center of W coated composites are reduced by 18.00% and 15.52%, the LAR of W coated composites decreases by 74.52% and 23.55%. Overall, the W coated composites depict good ablation property due to the high melting point of W coating, which can be resistant to high‐temperature oxidation and ablation, the sublimation of WO₃ carries away the heat.

     

喷雾干燥法金刚石-陶瓷结合剂复合烧结体的制备及表征

以金刚石和无机溶胶为原料,采用喷雾干燥法制备金刚石-陶瓷结合剂复合粉体,将粉体压制、烧结,获得金刚石-陶瓷结合剂烧结体。采用扫描电镜和激光粒度分析仪对复合粉体的形貌和粒径分布进行表征,借助综合热分析仪选取复合体的烧结温度,利用抗折试验机、扫描电镜和X射线衍射分别对喷雾干燥法和熔融法所制烧结试样的抗弯强度、断面形貌及物相进行分析。结果表明:经喷雾干燥的复合粉体为球形,易于成型,且复合粉体尺寸分布范围较宽,利于提高坯体致密度;选取金刚石-陶瓷结合剂复合体的烧结温度为820℃,在此温度下结合剂可实现对金刚石的黏结和包裹;烧结后,随陶瓷结合剂含量增加,两种工艺所制试样的抗弯强度均有提高,气孔率都相应降低;当结合剂含量为32%(质量分数)时,喷雾干燥法所制烧结试样的微观结构均匀,易析晶,抗弯强度和气孔率分别为99.46MPa和38.55%;熔融法所制试样的抗弯强度和气孔率分别为72.42MPa和39.89%。     

W/Cu功能梯度材料的制备及热循环应力分析

采用水煮溶解造孔剂法, 即先制备孔隙呈梯度分布的钨骨架、后渗铜的方法, 制备了W/ Cu 功能梯度材料, 并对钨铜在纵截面的分布进行了检测, 数据表明在纵截面上钨铜呈梯度分布。利用水淬法模拟其服役状况并用有限差分方法对产生的非稳态热应力进行了分析。结果表明, 热应力的最大值总是出现在两端, 由于富钨端相对密度较低, 裂纹总是在该端出现, 模拟结果与实验结果相一致。      

Synthesis of W-Y_2O_3 alloys by freeze-drying and subsequent low temperature sintering:Microstructure refinement and second phase particles regulation

In this work,W-Y2 O3 alloys are prepared by freeze-drying and subsequent low temperature sintering.The average size of reduced W-Y2 O3 composite powders prepared by freeze-drying method is only 18.1 nm.After low temperature sintering of these composite nanopowders,the formed W-Y2 O3 alloys possess a smaller grain size of 510 nm while maintaining a comparatively higher density of 97.8%.Besides a few submicron Y2 O3 particles(about 100-300 nm)with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries,lots of nano Y2 WO6 particles(<20 nm)exist in W matrix.Moreover,many Y6 WO12(<10 nm)particles exist within submicron Y2 O3 particles.The formation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases,resulting in the purification of W matrix and the strengthening of phase boundaries.The combined action of the above factors makes the hardness of the sintered W-Y2 O3 alloys in our work as high as 656.6±39.0 HV0.2.Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2 O3 alloys.     

Elevated temperature ablation resistance and thermophysical properties of tungsten matrix composites reinforced with ZrC particles

In order to improve the elevated temperature ablation resistance of the copper infiltrated tungsten materials (Cu/W) which are used as the rudders of the rocket motors at present, a new kind of tungsten matrix composites reinforced by 30 vol% zirconium carbide particles (ZrC_p/W) was developed, and the elevated temperature ablation resistance and thermophysical properties of the new materials were investigated. The values of the mass ablation rate and linear ablation rate of ZrC_p/W were much lower than that of Cu/W, which indicated that the addition of ZrC particles in tungsten matrix remarkably increased the ablation resistance. Thermal thermochemical oxidation of tungsten and ZrC particles was the main ablation mechanism of ZrC_p/W. A self-made dynamic responding multi-wavelength pyrometer was employed to measure the ablated surface temperatures and a thermal couple was employed to measure the back surface temperatures. The important temperature curves of the ablated surface and back surface of the specimens were successfully detected online, which indicated that ZrC_p/W has good thermal shock resistance. The present of ZrC particles in tungsten matrix remarkably decreased the thermal conductivity and thermal diffusivity of the ZrC_p/W composites, which is very useful for increasing the elevated temperature ablation resistance of the composites. The excellent elevated temperature ablation resistance of ZrC_p/W is attributed to the lower thermal conductivity, lower thermal diffusivity, oxidation resistance and high melting points. The good properties of ZrC_p/W makes it be suitable for the rudders for rocket motors instead of Cu/W.     

Solid-State Sintering of Tungsten Heavy Alloys

Solid-state sintering is a technologically important step in the fabrication of tungsten heavy alloys. This work addresses practical variables affecting the sinterability: powder particle size, powder mixing, and sintering temperature and time. Compositions containing 1 to 10 micrometer (μim) tungsten (W) powders can be fully densified at temperatures near the matrix solidus. Blending with an intensifier bar provided good dispersion of elemental powders and good as-sintered mechanical properties under adequate sintering conditions. Additional ball milling increases powder bulk density which primarily benefits mold and die filling. Although fine, 1 urn W powder blends have high sinterability, higher as-sintered ductilities are reached in shorter sintering times with coarser, 5 urn W powder blends; 10 urn W powder blends promise the highest as-sintered ductilities due to their coarse microstructural W.     

内嵌式钨铜粉末爆炸复合结构材料的研究

为满足托克马克核聚变装置内壁材料对W-Cu复合材料的需求,提出了内嵌式粉体爆炸复合方法和技术工艺。先用该方法制备内嵌式W-Cu粉复合材料,其实验粉末分别采用粒径3μm与23μm的纯钨粉和添加10%铜粉的W-Cu混合粉末(质量分数)。然后利用扫描电子显微镜、显微硬度计对内嵌式W-Cu粉复合材料进行表征、分析。结果显示,实验粉末经过爆炸烧结压实后能达到90%以上该密实材料的密度。添加10%铜粉后制备的W-Cu粉复合结构材料结合界面更加规则均匀理想,结合界面附近几乎没有孔隙,粉末压实部分孔隙度更小且孔隙的尺寸更小,均匀致密性更好,但粉末压实层硬度更低。使用粒径3μm的混合粉末与23μm的混合粉末,后者制备的W-Cu粉复合材料,粉末压实部分均匀致密性更好,孔隙度更小且孔隙的尺寸更小,粉末压实层密度更大,但硬度更低。     

Twinned Tungsten Carbonitride Nanocrystals Boost Hydrogen Evolution Activity and Stability

Synergistic integration of two active metal‐based compounds can lead to much higher electrocatalytic activity than either of the two individually, due to the interfacial effects. Herein, a proof‐of‐concept strategy is creatively developed for the successful fabrication of twinned tungsten carbonitride (WCN) nanocrystals, where W₂C and WN are chemically bonded at the molecule level. High‐angle annular dark‐field scanning transmission electron microscopy (HAADF‐STEM) and X‐ray absorption fine structure (XAFS) spectroscopy analyses demonstrate that the intergrowth of W₂C and WN in the WCN nanocrystals produces abundant N–W–C interfaces, leading to a significant enhancement in catalytic activity and stability for hydrogen evolution reaction (HER). Indeed, it shows 14.2 times higher and 140 mV lower in the respective turn‐over frequency (TOF) and overpotential at 10 mA cm^?2 compared to W₂C alone. To complement the experimental observation, the theoretical calculations demonstrate that the WCN endows more favorable hydrogen evolution reaction than the single W₂C or WN crystals due to abundant interfaces, beneficial electronic states, lower work function, and more active W sites at the N–W–C interfaces.