Printing Polymer Nanocomposites and Composites in Three Dimensions

Recent advances in materials science and three‐dimensional (3D) printing hold great promises to conceive new classes of multifunctional materials and components for functional devices and products. Various functionalities (e.g., mechanical, electrical, and thermal properties, magnetism) can be offered by the nano‐ and micro‐reinforcements to the non‐functional pure printing materials for the realization of advanced materials and innovative systems. In addition, the ability to print 3D structures in a layer‐by‐layer manner enables manufacturing of highly‐customized complex features and allows an efficient control over the properties of fabricated structures. Here, the authors present a brief overview mainly over the latest progresses in 3D printing of multifunctional polymer nanocomposites and microfiber‐reinforced composites including the benefits, limitations, and potential applications. Only those 3D printing techniques that are compatible with polymer nanocomposites and composites, that is, materials that have already been used as printing materials, are introduced. The very hot topic of 3D printing of thermoplastic composites featuring continuous microfibers is also briefly introduced.     

纳米技术在复合材料中的应用

纳米技术作为材料科学中的一个主要研究重点已经取得众多成就, 通过纳米粒子、纳米管以及各种超微细的结构模块, 导致产生出许多新的具有优异性能和新的应用可能的复合材料。本文介绍了纳米复合材料最新进展, 诸如纳米结构陶瓷, 无机有机复合材料和碳纳米管作填料的应用     

钛基复合材料及其制备技术研究进展

综述了钛基复合材料及其制备技术,重点介绍了纤维增强钛基复合材料(FTMCs)和颗粒增强钛基复合材料(PTMCs)的制备技术,分析了各种制备技术的优缺点.研究表明:纤维涂层法具有纤维分布均匀,纤维与界面反应小,复合材料性能优异等优点,是一种很有前景的FTMCs的制备技术.原位合成工艺制备的PTMCs避免了界面反应,界面清洁、结合强度高,可以明显提高PTMCs的力学性能.     

TiAl-B合金凝固过程中初生TiB2的固-液界面形态演变特征

用原位自生法制备了TiAl-B合金,并用XRD、SEM对材料的相组成、微观组织和初生TiB2晶体的界面结构特征进行了研究。结果表明：该合金主要由TiAl和TiB2两相组成;初生TiB2呈六面棱柱状,在其（0001）面存在清晰的生长台阶,凸台状或柱棒状分枝,它们的各晶面取向与母体的取向一致。分析表明,在TiAl-B合金凝固过程中初生TiB2晶体的固-液界面是不稳定的,使固-液界面由一完整光滑的界面逐渐演变为由多个相互独立的次级界面构成的复杂界面,次级界面亦为小面结构,具有相同的晶面取向关系。     

TiAl-B合金中初生TiB2晶体的表面形貌和形成机制

用原位自生法制备了Ti-40Al-xB(r(B)t%)合成并利用XRD、SEM对合金的相组成和微观组织进行了研究。结果表明：初生TiB2颗粒呈六面棱柱状,在其（0001）面存在凸台或棒状分枝,而在其{1010}面存在分布较均匀的薄片状凸面;有的初生TiB2的凸耳比较发达,凸耳呈一层层环状围绕初生TiB2晶体,这些凸台或棒状分枝及薄片状凸耳的晶面取向与母体的取向一致。分析表明,在不平衡凝固条件下,初生TiB2固－液界面前沿产生的富Al边界层和随着初生TiB2晶体的长大导致固－液界面上B原子过饱和度不均匀性增加的共同作用使固－液界面失稳,从而导致初生TiB2表面结构发生了变化,使初生TiB2(0001)面上的分枝具有较快的[0001]方向生长速度,呈棒状;而{1010}面上的凸耳具有较快的＜1010＞方向生长速度,使其呈片状。     

Microstructure Development and Mechanical Properties of Ni Matrix/Carbide Composites

Nickel alloy matrix/dispersed carbide (VC, NbC, WC) composites were prepared by either flame-spray, liquid phase sintering, or solid state sintering. A commercial Ni-B-Si alloy was mixed with 15% vol. of carbide particles and used to prepare composite coatings by flame-spray, bulk composite materials by solid state sintering (below 1045^°C) or liquid phase sintering (above 1050^°C). Phase characterization was performed by X-ray diffraction, optical microscopy, scanning electron microscopy and X-ray fluorescence in energy and wavelength dispersive spectroscopy modes. Similar microstructural features were produced by thermal spray and liquid phase sintering: a Ni-rich matrix and a boron-rich intergranular phase. Sintered samples showed higher wear resistance than the coatings obtained by flame spraying. In both cases the wear mechanism is dominated by the plastic flow of the Ni-rich ductile matrix and the fracture of a boron-rich intergranular phase, the latter serving as a retainer. Carbide removal was observed for solid state sintered samples.     

氯气刻蚀中孔碳化钛制备分等级孔结构炭材料

以钛酸正丁酯为钛源、蔗糖为炭源,采用溶胶-凝胶法制得有机-无机复合干凝胶,后经高温炭热反应、氯气化学刻蚀分别得到中孔碳化钛及碳化物基炭材料(CDCS).通过XRD、Raman、SEM、TEM和氮气吸附等表征,考察了钛酸正丁酯/蔗糖摩尔比例(R)对所制碳化钛和CDCS的孔结构和物理特性的影响.结果表明:在碳热过程所形成的中孔和大孔孔隙能够在氯气刻蚀过程中保持并传递给最终的炭材料.所制CDCS具有三种不同层次的孔隙结构,分别为氯气刻蚀碳化钛品体所产生的微孔、源自蔗糖残留炭中所含的3nm～4nm中孔以及炭颗粒间相互叠加和连接所形成的大孔.通过改变R比值,所制CDCS的BET比表面积和孔容分别在1479m2/g～1640m2/g和1.06cm3/g～2.03cm3/g之间可调.     

Effect of the composition and porosity of sintered titanium nanolaminates on their mechanical properties at high temperatures

By the methods of micro-and macroindentation, uniaxial compression, and scanning electron microscopy, we study the behavior of the structure and mechanical properties of mono-and biphase Ti₃SiC₂, Ti₃AlC₂, and Ti₄AlN₃ titanium nanolaminates (in-situ composites) prepared by the method of reaction sintering in compact and porous states. The regularities, specific features, and mechanisms of deformation and fracture processes are established for each material within the temperature range 20–1300°C. The temperature-strain and force boundaries of their existence in the plastic state are determined. The comparative analysis of the mechanical properties of nanolaminates is performed. It is shown that the strength characteristics of nanolaminates and their strain and creep resistance at medium and high temperatures increase in the following sequence: Ti₃AlC₂-Ti₄AlN₃-Ti₃SiC₂. The obtained picture of high-temperature properties of these materials is explained. It is shown that the procedure of prestraining of a porous material by ε = 4–8% may result in a significant increase in its specific high-temperature strength up to values higher than those typical of the compact material. __________ Translated from Problemy Prochnosti, No. 6, pp. 79–94, November–December, 2006.     

Ti-40Al-2B合金微观组织和初生TiB2生长特征

用原位自生法制备了Ti-40Al-2B(wt%)复合材料,并用XRD、SEM对复合材料的相组成和微观组织,特别是TiB₂的形貌进行了研究。结果表明:该合金由TiAl和TiB₂两相组成。其中TiB₂颗粒以初生的块状和共晶的片状或细棒状形式共存。初生TiB₂呈六面棱柱体,端面有清晰的生长台阶,其显露晶面分别为(0001)和｛101 - 0｝。结合晶体生长理论分析认为:TiB₂的生长单元为一个硼原子和六个钛原子组成的三棱柱,硼原子位于三棱柱的中心,生长方式以台阶式生长为主。其中｛112 - 1｝面生长速率最快,｛101 - 0｝面生长速率最慢,导致TiB₂形成以｛101 - 0｝面为棱柱面的六面棱柱结构。      

原位自生Ti-B-Si-C系复合材料的制备和性能

以Ti粉、B4C粉和SiC粉为原料,用真空热压烧结工艺制备了原位自生颗粒增强的Ti-B-Si-C系钛基复合材料,研究了复合材料的显微组织和力学性能。结果表明,使用的初始粉末不同,原位自生颗粒的组成不同,复合材料的性能也有明显的差别。     

用沉淀二氧化硅合成钛硅分子筛TS-2的研究

以沉淀二氧化硅为硅源,钛酸四丁酯为钛源,四丁基氢氧化铵为模板剂,采用水热晶 化法合成了TS-2分子筛.在优化合成步骤的基础上,采用XRD、FT-IR、UV-Vis、SEM 等测试方法系统研究了晶化温度、凝胶Si／Ti对晶化动力学行为及TS-2分子筛晶相结构的影 响.结果表明:高纯TS-2分子筛的最佳晶化温度为175℃,过高的晶化温度易导致MEL结构 向MFI晶相结构的转变及晶粒的逐渐长大.高纯TS-2样品的极限Ti／Si值为0.04,高于此值 则生成非骨架钛氧化物,并造成相对结晶度和催化氧化性能显著降低.