纳米晶体材料热稳定性的研究进展

纳米晶体材料独特的结构特征使其具有不同于传统多晶材料的优异性能,如何提高纳米晶体材料的热稳定性,避免其过度粗化,是近年来材料领域研究的热点课题。本文综述了国内外对纳米晶体材料热稳定性的研究进展,简要介绍了纳米晶体材料的微观结构特点,着重分析了溶质原子、第二相颗粒和微观应力等因素对纳米晶体材料晶粒长大的影响规律,介绍了纳米晶体材料的热力学和动力学稳定机制。     

含孔隙纳米晶体材料力学性能的计算模型

针对纳米晶体材料的微观结构,构建了一种复合相本构关系来描述纳米晶体材料的力学性能。纳米晶体材料由晶粒和晶界两部分组成,其中晶界相又包含两部分:晶界第一部分与晶界第二部分。晶界第一部分与晶粒应变相等,这两者的结合体又与晶界第二部分是等应力的,这更符合纳米晶材料的实际变形情况。然后,建立的模型被用以计算含孔隙纳米晶体材料的弹性模量,并将提出的计算含空隙纳米晶体材料弹性模量的模型拓展为描述纳米晶体材料小塑性变形条件下的应力-应变关系。计算结果与试验数据相比较表明,本模型可以较好地反映晶粒尺寸和孔隙率对纳米晶体材料弹性模量与屈服强度的影响。     

纳米晶体材料变形机制研究的最新进展

概述了纳米晶体材料结构研究的最新进展,着重讨论了纳米晶体材料的变形机制和分子模拟研究.最后给出了简要总结.     

非晶态合金向纳米晶体的相转变

利用非晶态合金的晶化过程可以形成纳米尺寸晶粒的多晶体材料（即纳米晶体），这种制备纳米晶体的方法近年来得到了广泛重视和深入研究，本文对这种制备方法和非晶态合金向纳米晶体的相转变动力学、热力学及转变机理等方面进行综述．     

非晶态合金向纳米晶体的相转变

利用非晶态合金的晶化过程可以形成纳米尺寸晶粒的多晶体材料（即纳米晶体），这种制备纳米晶体的方法近年来得到了广泛重视和深入研究，本文对这种制备方法和非晶态合金向纳米晶体的相转变动力学，热力学及转变机理等方面进行综述。     

纳米金属材料的界面力学行为研究

将常规多晶材料的粗晶粒尺寸缩小到纳米尺度时,这些纳米晶体材料会呈现出与其对应的粗晶材料迥异的物理现象.与材料力学行为最相关的是强度及塑形变形机理这两个方面.考虑到晶界的变形与破坏可能是纳米晶体材料低塑性的根源,克服纳米晶体材料中强度与韧性之间存在的"熊掌和鱼不可兼得"的问题,也通常称为晶界工程.在众多的晶界中,孪晶界面被发现可同时保持材料的强度和韧性.本文主要就纳米金属材料中界面的力学行为做一个简要综述,包含晶界的强化力学机理以及新型孪晶界面的力学行为与揭示内在尺度效应的模型研究.     

纳米金属间化合物NiAl的机械合金化合成及性能

利用机械合金化和高温热压工艺制备ＮｉＡｌ纳米晶体材料,并研究了材料的微观组织和力学性能。结果表明,ＮｉＡｌ的反应生成归结于机械碰撞诱发的爆炸反应机制,采用高温热压工艺可制备接近完全致密的纳米晶ＮｉＡｌ块体材料。ＮｉＡｌ纳米晶体材料的室温强度和塑性都高于铸态ＮｉＡｌ,纳米晶ＮｉＡｌ的高温强度依赖于应变速率,变形受扩散机制控制。     

电沉积法制备纳米晶材料

电沉积法是制备完全致密的纳米晶体材料最有前途的方法之一。本文综述了电沉积法制备纳米晶镍及其合金的研究现状及制备方法对纳米晶材料性质的影响。     

含孔隙多相纳米晶体陶瓷的力学性能计算模型

提出一个晶粒与晶界的混和模型，用于计算单相纳米晶体陶瓷的弹性模量，进而结合Budiansky等人的自洽模型计算了含孔隙多相纳米晶体陶瓷的弹性模量。在此基础上，将正割模量替代弹性模量，在等应变假设的前提下，将提出的能计算含孔隙多相纳米晶体陶瓷弹性模量的模型拓展成能描述该类材料在小塑性变形条件下的应力-应变关系的模型，并且确定σ0．2为含孔隙多相纳米晶体陶瓷的屈服强度。大量计算结果与试验数据的对比表明，所提出的模型能较好地反映晶粒尺寸与孔隙率对纳米晶体陶瓷弹性模量与屈服强度的影响。     

纳米SrAl2O4:Eu,Dy发光特性及浓度猝灭

用溶胶-凝胶法合成了不同Eu2+掺杂浓度的SrAl2O4Eu2+,Dy3+纳米晶体,探讨了纳米晶体的发光性能及浓度猝灭.结果发现纳米晶体与相应的常规尺寸的发光粉末材料相比,发射光谱和激发光谱的主峰位置均出现了明显的蓝移,发光强度和猝灭浓度有明显的提高,余辉衰减速度加快.认为蓝移现象以及余辉衰减变快,主要归因于发光粉体纳米粒子的量子尺寸效应.     

The mechanical behavior of multiphase nanocrystalline materials

Most commercial structural materials are multiphase and it is expected that multiphase nanocrystalline materials will also eventually be the materials of choice for applications. There has been limited research so far on the influence of second-phase particles in a nanostructured matrix. More studies have been carried out on nanoscale second phases in an amorphous matrix. This paper will review the examples from the literature of mechanical properties in nanocrystalline materials as influenced by second-phase particles. Work from the authors’ laboratory on nanoscale particles in nanocrystalline aluminum and iron will be emphasized. These particles include both “hard” and “soft” phases and exhibit a wide range of hardness behavior. Mechanisms for the observed effects will be suggested.     

“Bulk” Nanocrystalline Metals: Review of the Current State of the Art and Future Opportunities for Copper and Copper Alloys

It is a new beginning for innovative fundamental and applied science in nanocrystalline materials. Many of the processing and consolidation challenges that have haunted nanocrystalline materials are now more fully understood, opening the doors for bulk nanocrystalline materials and parts to be produced. While challenges remain, recent advances in experimental, computational, and theoretical capability have allowed for bulk specimens that have heretofore been pursued only on a limited basis. This article discusses the methodology for synthesis and consolidation of bulk nanocrystalline materials using mechanical alloying, the alloy development and synthesis process for stabilizing these materials at elevated temperatures, and the physical and mechanical properties of nanocrystalline materials with a focus throughout on nanocrystalline copper and a nanocrystalline Cu-Ta system, consolidated via equal channel angular extrusion, with properties rivaling that of nanocrystalline pure Ta. Moreover, modeling and simulation approaches as well as experimental results for grain growth, grain boundary processes, and deformation mechanisms in nanocrystalline copper are briefly reviewed and discussed. Integrating experiments and computational materials science for synthesizing bulk nanocrystalline materials can bring about the next generation of ultrahigh strength materials for defense and energy applications.     

表面科学与工程在纳米技术发展与应用中的直接作用

表面科学与工程在纳米技术的发展与应用中发挥着特殊的作用，尤其在纳米尺度材料的制备和纳米制造等领域。在纳米材料领域，纳米晶块材料的界面问题和纳米尺度的分子自组装的表面与界面问题是极富挑战性的前沿工作。在纳米制造领域，微机械部件的微纳米尺度的操作手设计和运动副表面的微观失效、摩擦磨损和润滑等问题也将开辟表面科学与工程新的研究领域。     

A polycrystalline mechanical model for bulk nanocrystalline materials using the energy approach

To systematically understand the grain size, strain rate and defect development dependent mechanical behavior of bulk nanocrystalline materials, a new constitutive model is proposed to describe the deformation mechanism, microstructure evolution and mechanical response of bulk nanocrystalline materials using the energy approach. In this model, the grain interior and grain boundary were not taken as two independent phases with different volume fractions, but as an integral object sustained dislocation and accommodated grain boundary sliding mechanisms. Meanwhile, defect creation and evolution and their effects on the overall stress–strain relation as well as the failure process of bulk nanocrystalline materials were considered in the model. For experimental verification, we have prepared nanocrystalline Ni powder by the DC arc plasma evaporation method. Bulk nanocrystalline Ni samples were then made by compaction and hot sintering. Experimental measurements on the mechanical response of bulk nanocrystalline Ni were performed under different strain rates and grain sizes. Comparison between experimental data and model predictions show that the method developed appears to be capable of describing the mechanical response of bulk nanocrystalline materials. The model applications to nanocrystalline Mg and Cu have shown that it can reflect the asymmetric defect development between tension and compression under quasi-static conditions; this results in its good capacity to describe the dynamic strain rate sensitivity and strain hardening behavior over a relatively large strain range under both compression and tension conditions.     

高科技的发展对硬质合金的影响和冲击

高科技的迅猛发展，对各个领域均有影响和冲击，硬质合金行业也不例外；在这场影响和冲击中，会促进硬质合金自身性能的提高，并导致向多功能、高功能、智能化、微型化发展；在纳米技术和原子材料的推动下，传统硬质合金性能会有新的突破，而涌现出新一代硬质合金。     

In situ joining of dissimilar nanocrystalline materials by spark plasma sintering

Joining of nanocrystalline materials will be a great challenge. In this paper, a reaction synthesis-based in situ joining technique was developed for joining dissimilar nanocrystalline materials by use of the spark plasma sintering (SPS) process. The joining technique combines the nanocrystalline material processing and joining operations into a single process.     

电磁场在材料加工中应用现状及发展趋势

电磁场作为一种可控的物理场,因其具有独特的性能而使其在材料科学研究和加工中的应用非常广泛.本文综述了电磁场在材料科学研究和加工中的应用现状及其发展趋势.最后指出电磁场传统应用技术的完善和优化、新的应用技术研究开发、复合场的应用研究将成为电磁场在材料科学研究和加工中发展方向.     

纳米(Ti,Ni,Fe)-Al金属间化合物及其复合材料研究进展

(Ti，Ni，Fe)-Al金属间化合物具有优良的性能，在航空材料和中高温结构材料等领域内具有重要的应用价值。采用机械合金化制备、合成纳米金属间化合物及其复合材料有望克服金属间化合物固有的室温脆性及高温蠕变强度低的缺陷。本文综合评述了国内外在纳米(Ti，Ni，Fe)-Al金属间化合物及其复合材料的机械合金化合成及其烧结固化与力学性能等方面所取得的主要研究成果，并就该研究领域的不足之处及其今后的发展方向提出了一些看法。     

Cladding of aluminum substrates with iron based wear resistant materials using controlled short arc technology

For lightweight constructions aluminum alloys are established since many years. Seal face and inlays, made of wear resistant materials, are commonly used to reach a partial wear protection for aluminum components. Problems concerning this approach are the necessary space and the endurance strength of the inlay-part joint. An alternative for the replacement of the inlays by cladding using innovative and easy to handle short arc technology will be discussed in this paper. The presented technology offers the potential to control the energy input into the substrate and so the formation of brittle intermetallic phases which occur in the aluminum-steel interface. The usage of wear resistant iron based feedstock materials enables further applications due to advantageous physical and mechanical properties. In the experiments the aluminum alloy AlSi8Cu3 was cladded with stainless steel and a nanocrystalline solidifying wear resistant iron based alloy using the coldArc equipment. Due to the low heat input, intermetallic phases could be minimized using stainless steel as cladding material as well as nanocrystalline solidifying iron based material. Further investigations in the resulting interface section, which did not exceed 10 µm, had been carried out by using SE-microscopy and energy-dispersive X-ray analysis.