纳米材料微阵列超塑微成形机理与尺度效应

微成形技术是未来批量制造高精密微小零件的关键技术,但是,微小尺度下材料的塑性变形行为不仅表现出明显的尺度效应,而且零件尺度已经接近常规材料的晶粒尺寸,每个晶粒的形状、取向、变形特征对整体变形产生复杂的影响,难以保证微成形的工艺稳定性。本项目采用纳米材料进行微成形,制造微阵列,零件内部包含大量的晶粒,可以排除晶粒复杂性的影响,而且纳米材料具有超塑性,在超塑状态下,变形抗力和摩擦力都明显降低,从而显著降低微成形工艺对模具性能的苛刻要求,提高工艺稳定性和成形精度。目前,纳米材料超塑性微成形技术方面的研究极少,变形时纳米材料的力学行为、变形机理、尺度效应、位错演化、力学模型等关键问题还有待研究。采用电沉积技术制备晶粒尺寸可控的纳米材料,将工艺实验研究、性能测试、组织分析、力学性能表征、数值模拟相结合,深入探究了纳米材料微阵列超塑性微成形机理和成形规律,以促进该技术的广泛应用。     

TiAl基合金的超塑性力学性能

超塑性力学性能是合理制定超塑性成形工艺和正确选用模具材料的理论依据。总结了国内外在TiAl基合金超塑性研究中所获得的各种条件下的超塑性力学性能。内容包括应变速率敏感性因子、超塑性延伸率和典型的真应力-真应变关系。最后，对TiAl其合金超塑性成形的应用前景进行了展望。     

600 MPa级相变诱导塑性钢的动态力学性能

目的研究相变诱导塑性钢不同应变速率下的力学性能,尤其是动态力学性能。方法对600 MPa级相变诱导塑性钢进行了准静态至动态6种不同应变速率下的力学性能测试,并对各试样断口处残余奥氏体含量进行了测试比对。0.001~0.01 s~(-1)准静态测试在ZWICK Z050万能试验机上完成,0.1,1,10,100 s~(-1)动态测试在ZWICK HTM5020液压伺服高速拉伸试验机上完成。结果力学测试结果表明,TRIP600具有明显的应变速率效应。在较高速率下,随应变速率的升高材料屈服强度、抗拉强度及伸长率都有一定程度的提高。结论断口处残余奥氏体含量在较高速率下无明显差别,表明较动态条件下应变速率对残余奥氏体转变影响不明显。     

纳米材料有更好的抗拉强度

美国国家标准技术研究所发现，像石英这类脆性材料，当制成纳米材料时可表现出很好的延展性。计算机模拟表明，材料在非晶态和晶体状态拉断过程中表现不同。     

金属硫化物纳米材料制备方法研究进展

对过渡金属硫化物纳米材料的研究进行了综述,阐述了ZnS、CdS、PbS、CuS等纳米材料的制备方法研究现状和发展前景,并对这些方法和成果进行了比较.     

块体金属纳米材料成形技术研究进展

介绍了通过纳米粉体制备块体纳米金属材料方面的进展情况,重点评价了制备纳米块体和纳米涂层的主要技术特点,指出了目前制备技术中存在的主要问题.介绍了一种新的块体纳米材料制备技术--低温球磨 中低温强加工技术.对块体金属纳米材料成形技术的发展趋势进行了展望.     

硅气凝胶纳米材料的力学性能与增韧

本文综述了低温超临界干燥制备的块状硅气凝胶纳米材料的力学性能特征，论述了材料密度与硅气凝胶的力学性能的关系。从材料的制备过程出发，指出了控制裂纹和提高硅气凝胶韧性的一些方法。简介了硅气凝胶纳米材料的制备与应用，讨论了热处理过程以及材料的微观结构对硅气凝胶材料强度和韧性的影响，给出了初步的结论     

热电纳米材料的研究进展

随着热电材料制备技术和性能研究的发展,热电纳米材料越来越受到人们的关注.介绍了几种有应用潜能的热电纳米材料的研究进展,指出了有关热电纳米材料研究存在的主要问题和其可能的发展方向.     

爆炸焊接对金属力学性能的要求

综述了爆炸焊接工艺对金属力学性能的要求，指出这种要求主要体现在金属的强度或塑性，以及它们的冲击韧性值上。     

Mechanical Properties, Damage and Fracture Mechanisms of Bulk Metallic Glass Materials

The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses （BMGs） and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.     

机械合金化─研制生产金属材料的一种新工艺

本文介绍了机械合金化的工艺特点。用机械合金化技术可以获得一些常规方法难以制备的新型合金及难以获得的独特性能，如生产ＯＤＳ合金和弥散强化复合材料，扩大合金元素在基体中的固溶度，获得非晶态合金（金属玻璃），合成金属间化合物材料，获得纳米结构材料。在金属材料研制生产中，机械合金化是一项值得大力研究开发的新技术。     

Incommensurately Modulated Structure in AgCuSe-Based Thermoelectric Materials for Intriguing Electrical,Thermal, and Mechanical Properties

AgCuSe-based materials have attracted great attentions recently in thermoelectric (TE) field due to their extremely high electron mobility, ultralow lattice thermal conductivity, and abnormal “brittle-ductile” transition at room temperature. However, although the investigation on the crystal structure of AgCuSe low-temperature phase (named as β-AgCuSe) was started more than half a century before, it is still in controversy yet, which greatly limits the understanding of its intriguing electrical, thermal, and mechanical performance. In this work, via adopting the advanced three-dimensional electron diffraction technique, this study finds that the AgCuSe-based materials crystalize in an incommensurately modulated structure with an orthorhombic Pmmn(0β1/2)s00 superspace group. The local lattice distortion in the incommensurately modulated structure has weak effects on the conduction band minimum due to the delocalized and isotropic feature of Ag 5s states, leading to high carrier mobility. Likewise, the inhomogeneous, weak, and anisotropic Ag-Se bonds result in the high degree of anharmonicity and ultralow lattice thermal conductivity. Furthermore, alloying S in AgCuSe reinforces the interaction between the adjacent Ag-Se layers, yielding the “brittle-ductile” transition at room temperature. This work well interprets the structure–performance relationship of AgCuSe-based materials and sheds light on the future investigation of this class of promising TE materials.     

Thermophysical Properties of Automotive Metallic Brake Disk Materials

The temperature distribution, the thermal deformation, and the thermal stress of automotive brake disks have quite close relations with car safety; therefore, much research in this field has been performed. However, successful and satisfactory results have not been obtained because the temperature-dependent thermophysical properties of brake disk materials are not sufficiently known. In this study, the thermophysical properties (thermal diffusivity, the specific heat, and the coefficient of thermal expansion) of three kinds of iron alloy series brake disk materials, FC250, FC170, and FCD50, and two kinds of aluminum alloy series brake disk materials, Al MMC and A356, were measured in the temperature range from room temperature to 500 °C, and the thermal conductivity was calculated using the measured thermal diffusivity, specific heat capacity, and density. As expected, the results show that the two series have significant differences in respect of the thermophysical properties, and to reduce the thermal deformation of the brake disk, the aluminum alloys with a high thermal conductivity and the iron alloys with low thermal expansion are recommended.     

金属纳米多层膜力学性能研究进展

新型功能材料及器件向小型化,集成化和复合化发展的趋势,使得尺寸在纳米尺度的层状材料和柔性多层器件在使用过程中的服役行为成为其发展的关键科学问题。本文结合作者近几年对Ag/M系列和Cu/M系列多层膜力学性能的研究工作,对金属纳米多层膜的微结构特征及其对力学性能的影响进行了回顾和总结,主要包括多层膜的晶粒形貌对其强化机制和塑性变形行为的影响,组元强度错配对多层膜硬化行为的影响,界面结构与其强度极值的关系、不对称界面结构引起的异常弹性模量增强和多层膜的室温蠕变机制及界面结构对蠕变性能的影响等几个方面,并对多层膜的力学性能研究进行了展望。     

Effect of Strain Rate on the Mechanical Properties of Ti-24Al-11Nb

The effect of strain rate on the bend ductility and notch fracture toughness of Ti-24Al-11 Nb wasstudied,it was found that the strain rate with a range of 1.17×10~(-5)～1.17 ×10~(-3) at 20℃ had nega-tive influence on both properties based on different microstructures.     

聚合物材料分子层次上力学问题的研究

基于原子力显微技术的单分子力谱法和光钳法可用于研究聚合物材料分子层次上存在的力学问题,包括聚合物分子链的强度、弹性性质及外力作用下的构象转变、分子间相互作用、聚合物分子的界面吸附以及聚合物表面的纳米粘弹性和纳米摩擦学等问题.     

One‐Dimensional Dielectric/Metallic Hybrid Materials for Photonic Applications

Explorations of 1D nanostructures have led to great progress in the area of nanophotonics in the past decades. Based on either dielectric or metallic materials, a variety of 1D photonic devices have been developed, such as nanolasers, waveguides, optical switches, and routers. What's interesting is that these dielectric systems enjoy low propagation losses and usually possess active optical performance, but they have a diffraction‐limited field confinement. Alternatively, metallic systems can guide light on deep subwavelength scales, but they suffer from high metallic absorption and can work as passive devices only. Thus, the idea to construct a hybrid system that combines the merits of both dielectric and metallic materials was proposed. To date, unprecedented optical properties have been achieved in various 1D hybrid systems, which manifest great potential for functional nanophotonic devices. Here, the focus is on recent advances in 1D dielectric/metallic hybrid systems, with a special emphasis on novel structure design, rational fabrication techniques, unique performance, as well as their wide application in photonic components. Gaining a better understanding of hybrid systems would benefit the design of nanophotonic components aimed at optical information processing.     

Bioinspired Materials with Self-Adaptable Mechanical Properties

Natural structural materials, such as bone, can autonomously modulate their mechanical properties in response to external loading to prevent failure. These material systems smartly control the addition/removal of material in locations of high/low mechanical stress by utilizing local resources guided by biological signals. On the contrary, synthetic structural materials have unchanging mechanical properties limiting their mechanical performance and service life. Inspired by the mineralization process of bone, a material system that adapts its mechanical properties in response to external mechanical loading is reported. It is found that charges from piezoelectric scaffolds can induce mineralization from surrounding media. It is shown that the material system can adapt to external mechanical loading by inducing mineral deposition in proportion to the magnitude of the stress and the resulting piezoelectric charges. Moreover, the mineralization mechanism allows a simple one-step route for fabricating functionally graded materials by controlling the stress distribution along the scaffold. The findings can pave the way for a new class of self-regenerating materials that reinforce regions of high stress or induce deposition of minerals on the damaged areas from the increase in mechanical stress to prevent/mitigate failure. It is envisioned that the findings can contribute to addressing the current challenges of synthetic materials for load-bearing applications from self-adaptive capabilities.     

聚乙烯纤维制备超高延性水泥基复合材料的试验研究

为进一步提升高性能水泥基复合材料的拉伸能力,研制了以短切超高分子量聚乙烯纤维作为增强材料,以水泥砂浆为基体的超高延性水泥基复合材料(Ultra-high ductility cementitious composites, UHDCC)。本研究通过直接拉伸、单轴抗压及三点弯曲梁试验研究了UHDCC的基本力学性能。直拉试验表明,UHDCC具有优异的应变硬化和多重裂缝开裂性能。在极限状态下,UHDCC的裂纹间距小于2 mm,最大平均裂纹宽度小于200 μm;材料的平均抗拉强度为7.28 MPa,峰值强度处的平均拉伸应变达到12%,最大拉伸应变达到13%以上,具有超高的拉伸延性。轴压试验表明,超过峰值强度后,UHDCC在80%和60%的抗压峰值强度处的应变分别约为2.8%和7.0%,说明材料具有强大的受压变形能力。材料的弯曲韧性指数I10、I30、I50、I60分别为10.1、33.1、54.4、65.6,表明UHDCC具有优异的弯曲变形能力。此外,三点弯曲缺口梁和单裂缝试验结果表明,UHDCC的超高延性源于聚乙烯纤维超高的裂缝桥接能力。