激光烧结石墨烯-铜纳米复合材料性能研究

石墨烯拥有许多优异的性能,这些性能使石墨烯有望成为金属基复合材料的理想增强相。采用激光烧结的方法制备了石墨烯-铜纳米复合材料。X射线衍射（XRD）和Raman光谱测试结果表明,石墨烯存在于激光烧结所制备的纳米复合材料中。显微硬度测试结果显示,石墨烯的添加使得石墨烯-铜纳米复合材料的硬度比激光烧结纯铜的硬度提高了约22%。用电化学极化法研究了激光烧结的石墨烯-铜纳米复合材料和纯铜在3.5%（质量分数）NaCl 溶液中的腐蚀行为,石墨烯-铜纳米复合材料的腐蚀电位比激光烧结纯铜的腐蚀电位略有降低,腐蚀电流也有所降低,说明其耐腐蚀性能较激光烧结纯铜略好。     

激光烧结石墨烯铜复合材料温度场有限元模拟

在激光烧结石墨烯增强铜基复合材料的过程中,了解瞬时温度场分布对优化工艺参数、控制烧结质量有重要作用。建立了激光烧结预涂在42CrMo基板上的石墨烯铜的混合粉末的有限元模型。研究了激光烧结过程温度场分布,熔池的几何参数以及烧结层与基体的冶金结合宽度。为了验证模拟结果,使用与模拟相同的参数进行了单道激光烧结的实验。研究表明,热传导、热辐射和相变潜热在激光烧结过程的温度场分布中起重要作用。实验结果与模拟结果较为一致。所以可以依据模拟结果预测实验的温度场分布和熔池几何参数,同时也可以据此优化激光烧结参数。     

石墨烯/银纳米复合材料的制备及其影响因素研究

以硝酸银、鳞片石墨为原料, 在强碱环境下, 制备得到石墨烯/银纳米复合材料, 采用X射线衍射、红外吸收光谱、透射电子显微镜、紫外可见分光光度计对所制备的石墨 烯/银纳米复合材料进行了表征.结果表明: 氧化石墨烯和银离子在强碱NaOH的作用下, 氧化石墨烯失去部分含氧官能团, 被部分还原为石墨烯(rGO), 银离子被还原为纳米银颗粒, 均匀分布在氧化石墨烯片层表面, 颗粒大小和分布受硝酸银用量、反应温度、NaOH的加入顺序及前驱物混合方式等因素影响, 在GO与Ag粒子质量比为 1:1.08时, 负载在石墨烯片层上的银纳米颗粒集中在12 nm左右. 关键词： 石墨烯/银纳米复合材料 强碱溶液     

CVD合成的掺杂BNx-石墨烯纳米复合材料:结构和发光性能

用B₄C为硼源,利用CVD系统在N₂-H₂等离子体中合成了掺杂BN_x纳米棒,接着在掺杂BN_x纳米棒表面用CH₄生长了石墨烯纳米片,制备出掺杂BN_x-石墨烯三维纳米复合材料。一系列表征结果说明合成的纳米复合材料由C和O共掺杂的BN_x纳米棒和石墨烯纳米片组成,其形成与碳氢基团的转换和掺杂BN_x纳米棒的形变在石墨烯纳米片中产生的应力有关。室温发光性能表明石墨烯纳米片对掺杂BN_x纳米棒的紫外光和绿光有明显的猝灭作用,起源于掺杂BN_x-石墨烯界面上的电荷转移和电子散射。     

基于石墨烯的Au纳米颗粒增强染料随机激光

石墨烯和纳米颗粒的复合材料具有新颖的光学和电学特性,被广泛应用于信息传感、光电转换、医学诊断等领域,具有十分广阔的发展前景.虽然石墨烯拥有优异的光电性能,可以实现对随机激光性质的调控,但目前实现特殊结构的石墨烯与金属纳米结构的复合过程复杂繁琐,利用石墨烯有效降低随机激光阈值仍存在挑战.本文利用便捷的化学还原及吸附法制备Au/石墨烯结构,以染料DCJTB为增益介质,使用旋涂法制备了均匀的薄膜样品;研究对比Au纳米颗粒和Au/石墨烯结构随机激光特性,分析了石墨烯的作用机理.研究结果表明,Au/石墨烯复合材料透射峰与增益介质的光致发光光谱峰最为接近,对于染料分子的能级迁跃起到了促进作用.在相同的增益介质中,石墨烯的加入不仅使得光子在无序介质中散射频次增加,促进了增益效果,而且增强了Au纳米颗粒表面的等离子体共振效应.二者相互协同,展现出了优异的随机激光特性,阈值降低至2.8μJ/mm~2;对样品重复测量可得样品的激射重复性较强、品质较高.本研究对促进随机激光应用、实现高性能的光电器件起到了一定的推动作用.     

石墨烯/铝基复合材料在纳米压痕过程中位错与石墨烯相互作用机制的模拟研究

石墨烯因其优异的力学性能已成为增强金属基复合材料的理想增强体.然而,目前对石墨烯/金属基复合材料在纳米压痕过程中嵌入石墨烯与位错之间的相互作用仍不清晰.本文采用分子动力学模拟方法,对90°,45°和0°位向的石墨烯/铝基复合材料进行了纳米压痕模拟,研究了压痕加载和卸载过程中石墨烯/铝基复合材料的位错形核及演化,以获取不同位向的石墨烯与位错的相互作用机制,并分析其对塑性区的影响.研究发现,石墨烯可以有效阻碍位错运动,并且石墨烯会沿着位错滑移方向发生弹性变形.在纳米压痕过程中,位错与不同位向石墨烯之间的相互作用差异导致塑性区的变化趋势不同.研究结果表明,在石墨烯/铝基复合材料中,位向不同的石墨烯对位错阻碍强度和方式不同,且石墨烯位向为45°的复合材料的硬度高于其他模型.此外,石墨烯/铝基复合材料的位错线总长度的演化规律与石墨烯位向紧密相关.本文研究可为设计和制备高性能石墨烯/金属基复合材料提供一定的理论指导.     

强激光辐照下纳米晶体铜薄膜层裂破坏的实验研究

采用强激光辐照加载技术和激光速度干涉(VISAR)测试技术，对纳米晶体铜薄膜的层裂特性进行实验测量和分析.基于VISAR实测的自由面速度波形，计算得到纳米晶体铜薄膜在超高拉伸应变率下的层裂强度高达3 GPa，明显高于多晶铜的层裂强度, 其原因归咎于纳米晶体材料中存在大量晶界阻碍了位错运动.     

强激光辐照下纳米晶体铜薄膜层裂破坏的实验研究

采用强激光辐照加载技术和激光速度干涉(VISAR)测试技术,对纳米晶体铜薄膜的层裂特性进行实验测量和分析.基于VISAR实测的自由面速度波形,计算得到纳米晶体铜薄膜在超高拉伸应变率下的层裂强度高达3 GPa,明显高于多晶铜的层裂强度, 其原因归咎于纳米晶体材料中存在大量晶界阻碍了位错运动. 关键词： 纳米晶体铜薄膜 层裂 激光辐照     

纳米壳聚糖复合材料的制备与性能研究

为了提高壳聚糖的水溶性及其止血方面的性能,将壳聚糖(CS)纳米化,并引入具有抗菌作用的Ag~+离子和凝血辅助作用的Ca~(2+)离子,制备出纳米壳聚糖金属离子复合止血材料。首先,采用离子交换法制备纳米壳聚糖(nmCS),再分别加入AgNO_3和饱和CaCl2溶液,制得nmCS-Ag、nmCS-Ca、nmCS-Ag-Ca复合材料。然后,采用FTIR、XRD、SEM等手段对复合材料的结构进行表征。最后,对复合物的凝血、止血性能进行了测试。实验结果表明:改性后的壳聚糖IR图谱在1647cm-1和1560cm-1处出现了纳米壳聚糖钠盐的特征吸收峰;复合了金属离子的纳米壳聚糖在XRD图谱中表现出了Ag~+、Ca~(2+)的晶型特征;扫描电镜显示nmCS-Ag中Ag~+有部分析出而nmCS-Ca的复合效果较好;nmCS-Ag-Ca的凝血、止血效果要优于nmCS-Ag和nmCS-Ca,同时nmCS-Ag和nmCS-Ca的凝血、止血效果要优于nmCS。测试结果表明,成功制备了纳米壳聚糖金属离子复合止血材料。     

基于纳米铜/石墨烯包覆光子晶体光纤的 硫化氢气体传感性能研究

提出一种基于纳米铜/石墨烯包覆光子晶体光纤的硫化氢传感方法.将两根单模光纤分别与实心光子晶体光纤进行粗锥熔接,形成马赫-曾德干涉结构.先在光子晶体光纤表面包覆石墨烯薄膜,再在石墨烯薄膜的表面沉积纳米铜形成复合敏感薄.当复合敏感薄膜吸附硫化氢气体时,其自身折射率发生改变,导致光子晶体光纤中纤芯与包层的光程差发生变化,干涉波谷发生偏移.建立气体浓度与波长偏移关系,实现硫化氢的低浓度检测.研究表明:该传感器的灵敏度为8.5pm/ppm,检测限为3.85ppm,在硫化氢浓度为0～80ppm范围内呈现良好的线性和选择性,其输出光谱呈现蓝移,响应时间和恢复时间分别约为92s和119s.该传感器成本低、结构简单、制作容易,有望应用于硫化氢气体的探测.     

Direct laser sintered WC-10Co/Cu nanocomposites

In the present work, the direct metal laser sintering (DMLS) process was used to prepare the WC-Co/Cu nanocomposites in bulk form. The WC reinforcing nanoparticles were added in the form of WC-10 wt.% Co composite powder. The microstructural features and mechanical properties of the laser-sintered sample were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX), and nanoindentation tester. It showed that the original nanometric nature of the WC reinforcing particulates was well retained without appreciable grain growth after laser processing. A homogeneous distribution of the WC reinforcing nanoparticles with a coherent particulate/matrix interfacial bonding was obtained in the laser-sintered structure. The 94.3% dense nanocomposites have a dynamic nanohardness of 3.47 GPa and a reduced elastic modulus of 613.42 GPa.     

Pulsed laser deposition of polymer-metal nanocomposites

Different polymer-metal nanocomposites, metal clusters on a polymer surface and for the first time also polymer/metal multilayers, were pulsed laser deposited at a wavelength of 248 nm. Poly(methyl methacrylate) (PMMA) and Bisphenol A dimeth-acrylate (BisDMA), which strongly differ in their hardness of 3 and 180 N/mm², respectively, were taken as polymer components. Metals Ag and Cu were chosen because of their different reactivity to polymers. When depositing Ag on PMMA, spherical clusters are formed due to high diffusion and total coalescence. For Cu, much smaller grains with partially elongated shapes occur because of lower diffusivity and incomplete coalescence. Compared to the results on the soft PMMA, the clusters formed on the harder BisDMA are much larger due to higher diffusivity on this underlayer. In PMMA/Cu multilayers, wavy layered structures and buckling is observed due to relaxation of compressive stress in the Cu layers. Smooth Cu layers with higher thicknesses can only be obtained, when the hardness of the polymer is sufficiently high, as in the case of BisDMA/Cu multilayers.     

Corrosion properties of aluminium coatings deposited on sintered NdFeB by ion-beam-assisted deposition

Pure Al coatings were deposited by direct current (DC) magnetron sputtering to protect sintered NdFeB magnets. The effects of Ar⁺ ion-beam-assisted deposition (IBAD) on the structure and the corrosion behaviour of Al coatings were investigated. The Al coating prepared by DC magnetron sputtering with IBAD (IBAD-Al-coating) had fewer voids than the coating without IBAD (Al-coating). The corrosion behaviour of the Al-coated NdFeB specimens was investigated by potentiodynamic polarisation, a neutral salt spray (NSS) test, and electrochemical impedance spectroscopy (EIS). The pitting corrosion of the Al coatings always began at the voids of the grain boundaries. Bombardment by the Ar⁺ ion-beams effectively improved the corrosion resistance of the IBAD-Al-coating.     

Fast femtosecond laser ablation for efficient cutting of sintered alumina substrates

Fast, accurate cutting of technical ceramics is a significant technological challenge because of these materials' typical high mechanical strength and thermal resistance. Femtosecond pulsed lasers offer significant promise for meeting this challenge. Femtosecond pulses can machine nearly any material with small kerf and little to no collateral damage to the surrounding material. The main drawback to femtosecond laser machining of ceramics is slow processing speed. In this work we report on the improvement of femtosecond laser cutting of sintered alumina substrates through optimisation of laser processing parameters. The femtosecond laser ablation thresholds for sintered alumina were measured using the diagonal scan method. Incubation effects were found to fit a defect accumulation model, with F_th,1=6.0 J/cm² (±0.3) and F_th,∞=2.5 J/cm² (±0.2). The focal length and depth, laser power, number of passes, and material translation speed were optimised for ablation speed and high quality. Optimal conditions of 500 mW power, 100 mm focal length, 2000 µm/s material translation speed, with 14 passes, produced complete cutting of the alumina substrate at an overall processing speed of 143 µm/s – more than 4 times faster than the maximum reported overall processing speed previously achieved by Wang et al. [1]. This process significantly increases processing speeds of alumina substrates, thereby reducing costs, making femtosecond laser machining a more viable option for industrial users.     

TC_4合金TiN激光表面合金化层的组织和硬度研究

通过采用CO_2激光对TC_4合金进行TiN表面合金化处理,探讨了激光功率对合金化层组织和硬度的影响。结果表明,激光合金化试样存在组织不同的三个区域,分别为TiN合金化层,基底熔凝层和淬火层。TiN合金化层由钛合金基体和TiN组成,其中TiN呈现颗粒和树枝晶两种形态。基底熔凝层为定向生长的柱状晶,基底淬火层为针状马氏体。TiN激光合金化层的硬度在700～1100HV之间,约为TC_4合金的2～4倍。     

Thermal resistance of sintered powder-liquid 3He boundary

Heat transfer between normal liquid ³He and sintered powders is investigated in terms of the Landau Fermi liquid theory. It is shown that the coupling between zero sound in ³He and low energy vibrational modes in sinter gives the extra contribution to the heat transfer below about 10mK. Theoretical results are compared with experimental data from 2mK to 100mK.     

Interface structure and radiation damage resistance in Cu-Nb multilayer nanocomposites

We use atomistic simulations to show that upon removal or insertion of atoms, misfit dislocations in Cu-Nb interfaces shift between two adjacent planes, forming pairs of extended jogs. Different jog combinations give rise to interface structures with unlike densities but nearly degenerate energies, making Cu-Nb interfaces virtually inexhaustible sinks for radiation-induced point defects and catalysts for efficient Frenkel pair recombination.