关键词： 微结构   陶瓷   陶瓷基复合材料   精密磨削   电火花加工   PCD  

摘要： 蓝宝石、聚晶金刚石（PCD）、单晶碳化硅陶瓷、陶瓷基复合材料等高性能硬脆材料具有硬度高、密度低、热膨胀系数小、化学稳定性好等特点,在其表面加工制造出规则的微结构可以附加出新的功能特性,被广泛应用于航空航天、汽车制造、生物工程等领域。然而,这些材料硬度或脆性较高,导致其微结构加工表面容易出现破损、崩边等问题,很难保证微结构的3D形状精度。论文提出采用高精度的微细磨削加工技术在蓝宝石、硬质合金、陶瓷及陶瓷基复合材料表面加工制造出高形状精度的微阵列结构,对比研究不同材料微结构加工的形状精度和表面质量;采用电火花磨削复合加工技术在PCD刀具表面加工制造出螺旋沟槽结构,并探索PCD刀具的钻削性能。论文主要研究内容和结果如下:（1）采用机械修整技术将金刚石砂轮修整成V形尖端,然后利用精密修整后的V尖端砂轮在单晶碳化硅陶瓷、蓝宝石玻璃、陶瓷基复合材料等材料表面加工出微阵列结构,并且对比研究不同材料表面微结构加工的形状精度和表面质量。单晶碳化硅、铝基碳化硅、反应烧结碳化硅、微晶玻璃陶瓷表面的微结构磨削形状精度PV值分别为12.6μm、13.7μm、11.3μm、17.9μm,蓝宝石玻璃微结构表面粗糙度R为0.942μm,微结构尖端圆弧半径为17.37μm。（2）采用干式接触放电（ECD）修整技术可以对金属基金刚石砂轮进行高效修锐修整,研究了脉冲放电参数对金属基砂轮尖端修整精度的影响,优化的脉冲放电参数为:开路电压25 V,脉冲频率4000 Hz,占空比50%;精密放电修整后的砂轮尖端圆弧半径最小可达15μm,尖端角度误差最小可达2.4°。采用修整后的V尖端金刚石砂轮在硬质合金表面加工微结构,获得的微结构深度误差最小为2.6μm,底部圆弧半径误差最小为3.2μm,沟槽侧面粗糙度R为0.31μm。（3）采用电火花磨削复合加工技术在PCD刀具表面可以高效加工出螺旋沟槽结构,研究了电火花磨削复合加工参数对PCD刀具刃磨质量的影响。在PCD刀具的电火花磨削复合加工过程中,脉冲放电参数对PCD刀具螺旋沟槽加工质量的影响从大到小依次为脉冲电流、脉冲电压、脉冲宽度、脉冲间隔,较优的脉冲电流、脉冲电压、脉冲宽度分别是1400 m A、95 V、400 ns。脉冲间隔对PCD刀具刃磨质量影响较小,当脉冲电压为95 V时,PCD刀具沟槽表面粗糙度R为0.156μm,PCD刀具钻削性能最好,铝基碳化硅钻孔质量最好。

关键词： 热电材料   Cu2Se   掺杂   纳米第二相  

摘要： 近年来,随着经济的快速发展,能源的消耗日益增多,由此引发了严重的能源危机问题以及环境污染问题,对人类社会的发展以及生活造成了许多不良的影响,寻找新型清洁能源技术迫在眉睫。热电材料是一种能将热能和电能进行相互转换的材料,具有无污染、无噪音、寿命长等优点,但由于其转换效率低,多用于航空航天等高端领域,难以大规模商用,而寻求高性能热电材料以及提升现有热电材料的热电优值(ZT值)为解决这一问题提供了无限可能。CuSe基热电材料是典型的类液态材料之一,高温下Cu离子的自由迁移性使其具有较低的晶格热导率以及较高的热电性能。不仅如此,其还具有原材料储量丰富、价格低廉、无毒且制备工艺简单等诸多优点,故本文选取CuSe为研究对象,探究了元素掺杂、引入纳米第二相以及增加纳米孔洞对其热电性能的影响。本文中所有所需目标样品均是通过水热法和热压法制备的,并对其物相结构以及电输运性能、热输运性能进行测试分析。首先,以CuSe为基底,进行微量Pb掺杂和Lu掺杂,研究元素掺杂对其热电性能的影响。接着,在CuSe和CuLiSe材料的基础上,引入零维碳纳米材料碳点(CDs)作为纳米第二相,探究其对热输运性能以及电输运性能的影响。最后,将CuSe粉末与研磨好的CH和NHHCO有机粉末混合均匀,高温烧结调控其纳米孔洞,探究纳米孔对CuSe材料ZT值的影响。通过分析实验数据发现,虽然Pb掺杂降低了载流子浓度和迁移率,功率因子下降,但增加了点缺陷,降低了晶格热导率,改善了热输运性能,综合作用下材料的热电性能有所提升。Lu掺杂使电输性能恶化,最终ZT值并没有升高。CDs的引入能够细化晶粒,增强声子散射,降低晶格热导率;尽管由于载流子迁移率降低,其电输运性能有所下降;但仍有利于材料ZT值的提升。通过引入纳米孔洞的方法优化CuSe的热电性能是非常有效且便捷的,孔洞增多能有效散射声子,降低了材料的晶格热导率,电输运性能也有所提升。但是需要注意,孔洞尺寸、均匀性等均会影响材料的热电性能,该实验仍需进一步探索。最终,对于Pb掺杂的CuSe系列样品,CuPbSe的ZT值在973 K达到了1.6,比纯样性能提升了34.7%左右;Lu掺杂系列样品的电输运性能最高提升了33.3%;CDs弥散系列样品的最高ZT值在CuSe+0.8 wt%和CuLiSe+0.015 wt%中获得,温度为973 K时,分别为1.98和1.67。

关键词： 氧化铋薄膜   磁控溅射   氧氩流量比   微结构   光电性能  

摘要： 为了制备出不同光电性能的氧化铋薄膜,并明晰其性能机理,以便后续研究与氧化锌薄膜复合成压敏薄膜。采用磁控溅射法,改变溅射气氛中氧气和氩气的流量比,在玻璃衬底上制备出了三个氧化铋薄膜样品,并对其微观形貌、结构及光电性能进行了测试分析。结果表明:溅射气氛中的氧氩流量比对薄膜微结构及光电性能影响显著;不同氧氩流量比制备的Bi_(2)O_(3)薄膜中均含BiO_(2)和Bi杂相,且随着氧氩流量比由0∶40增大至4∶36,薄膜中Bi含量减少,BiO_(2)增加;薄膜颜色由黑变黄;沉积速率由14 nm/min减少至12 nm/min;晶粒尺寸增大,表面趋向致密均匀,可见光区透过率由0.25%增加到56.73%;禁带宽度由0增加到3.17 eV;载流子浓度、导电性能急剧降低,调节溅射气氛中氧氩流量比可有效控制氧化铋薄膜的禁带宽度,载流子浓度等,从而获得不同光电性能的薄膜样品。

关键词： microstructures   selective laser melting   stainless steel   superalloys   textures  

摘要： Choosing a properly optimized rotating scan strategy during the selective laser melting (SLM) process is essential to reduce residual stresses and thus to obtain homogeneous properties. Surprisingly, anisotropic material properties are found in several materials that are built with the often applied rotating stripes scan strategy of Electro-Optical Systems (EOS) because the scan strategy avoids possible interactions of the laser beam with process by-products and therefore excludes a range of scanning directions. Herein, the alloys Hastelloy X, Inconel 718, and stainless steel 316L are investigated. Vertically built specimens with a cylindrical gauge geometry show an oval deformation during tensile testing, indicating a mechanical anisotropy in the horizontal x- and y-direction. Tensile tests along the x- and y-direction reveal a deviation of the yield strength of 7% for Hastelloy X. Analyses of the microstructures show differences in the grain morphology, size, and texture in all three coordinate planes of the three materials. This anisotropic behavior can be explained by a detailed study of the texture and the calculated Schmid factors. Heat treatments can reduce the textural and mechanical anisotropy due to recrystallization of grains but requires annealing at sufficiently high temperatures and long times.

关键词： 纳米材料  

ISBN: (纸本)9787576500745

摘要： 人工光子微结构材料在信息传输、天线、雷达、网络、隐身等领域都有许多应用。本书从光子晶体、超材料和表面等离激元的基本概念出发，依据带隙调控、局域共振原理，采用数值仿真设计模型和微波实验研究，总结和探讨了二维光子晶体“未激发”能带，损耗对单负超材料传输的影响，双曲超材料高波矢特性及平带引起的单向传输特性，人工光子微结构材料中的类量子效应等内容，为研制新型高性能光子器件提供了方法。

关键词： Flash sintering   Microstructure evolution   Zinc oxide   Thermal insulation   Grain size  

摘要： The present work aimed to reduce the microstructure heterogeneity inherent to flash sintering by using alumina blankets as a thermal insulator around ZnO cylindrical samples during the sintering process, under different electric field conditions. Thermal insulation significantly reduced the flash onset temperature and the grain size heterogeneity. For higher electric fields, a temperature reduction as high as 480 degrees C was observed, which also led to lower densification. These findings were discussed in terms of changes in the heat loss dynamics coupled with the adsorbed water retention, both promoted by the applied thermal insulation. A model to estimate the temperature at stage III of flash sintering was proposed. The final temperature reached with thermal insulation did not differ significantly from the ones without it. Thus, thermal insulation could represent an alternative route to flash sinter materials with lower furnace temperatures with energy savings up to 78 % and a more homogeneous microstructure.

关键词： 反应熔渗   C/C-SiC复合材料   氧乙炔烧蚀   微结构  

摘要： 以无纬布/网胎0°/90°叠层穿刺三维四向预制体为增强体,采用化学气相渗透(chemical vapor infiltration,CVI)、树脂浸渍碳化(polymer infiltration carbonization,PIC)与反应熔渗(reactive melt infiltration,RMI)复合工艺制备穿刺C/C-SiC复合材料,研究其微观组织及在C2H2-O2焰中的烧蚀行为.结果 表明:无纬布、穿刺纤维束由CVI+PIC制备的碳基体填充而形成致密C/C区域,RMI生成的SiC主要位于网胎层中,其含量为37.3％(质量分数).复合材料表面因过量硅化而形成了SiC富集层.当烧蚀距离为20 mm、O2∶C2H2=2∶1时,烧蚀600 s后材料X-Y、Z向线烧蚀率分别为0.8×10-4、3.6× 10-4 mm/s,比先驱体浸渍裂解(polymer infiltration pyrolysis,PIP)工艺制备C/C-SiC材料烧蚀率小1个数量级.烧蚀面SiC富集层保护及被动氧化作用是材料具有优异抗氧化烧蚀性能的主要原因.随烧蚀距离由20 mm向10 mm减小,复合材料烧蚀率先缓慢变化后快速增大,烧蚀率快速增长阶段复合材料发生主动氧化烧蚀.

关键词： Electrodes  

摘要： Fast discharge capability of automotive batteries not only affects the acceleration and climbing performance of electric vehicles, but also the accessible driving range under complex driving cycles. Understanding the intricate physical and chemical processes across multiple length-scales is critical to assist the strategic design of electrodes for improved rate performance. Here, we correlate the discharge rate performance of Ni-rich LiNi1-x-yCoxMnyO2 (NMC) cathodes to the electrode architectures, ranging from the crystallographic orientations, surface morphology and cracks at single particle level, to the factors that affect the dominance of the solid and liquid-state transport (SST and LST) at electrode level. A random orientation of the primary particles is found to incur an increase of the SST resistance by a factor of 2.35 at 5C and a heterogeneous intra-particle lithiation. Internal cracks significantly restrict the accessibility to the active material. Double-layered particles are proved to be a more promising candidate than single-crystal particles. At electrode level, the SST-dominance depth is quantified for the first time to guide the microstructural tuning and rational operating windows are proposed for electrodes of various architectures. The reaction front is observed to shuttle across the electrode depth to mitigate the polarization, which can provide valuable insights into the battery management development. Finally, by comparing the performance of single crystal and polycrystalline NMC811 electrodes, it is suggested that electrode thickness and porosity are more critical in the former for enhanced discharge rate performance, in contrast to polycrystalline electrodes, in which a gradient particle fraction and size distribution are recommended.

关键词： 微结构可控材料   跨尺度   增材制造   生物医学  

摘要： 微结构可控材料是一类利用微观结构调控整体性能的新材料.在不改变材料本身物理化学性质的条件下,通过控制微结构组成单元的尺寸、几何构型、排列方式提升宏观材料的力学、热学、表界面等性质.在微结构可控材料的研究中,性能调控的关键在于跨尺度分级结构的精准构筑.本文从制备工艺出发概述了微结构可控材料的最新研究进展,着重介绍了聚合物、金属及无机材料的跨尺度微纳加工方法对于整体性能的提升作用,并总结了微结构可控材料在生物医学领域中低密度材料、微液滴操控、微型机器人等方面的应用,展望了其未来的发展方向.