纳米金属多层膜微观结构及其力学性能研究进展

纳米金属多层膜由于其微观结构的可调控性和优异的力学性能受到广泛关注，而建立微观结构与力学性能的内在联系则是设计制备高性能纳米金属多层膜的基础。结合当前国内外关于纳米金属多层膜微观结构和力学性能的最新研究进展，总结了晶体/晶体和晶体/非晶纳米金属多层膜的微观结构特征及其对力学性能的影响，基于位错强化模型，阐述了微观特征尺寸与力学性能之间的关系。现有研究结果表明，由于组元材料本征特性的差异以及强烈的尺寸与异质约束效应，不同组元材料构成的纳米金属多层膜具有不同的晶粒形貌和界面类型与结构，这对其强度/硬度、拉伸延性和变形行为具有显著影响。金属多层膜的力学性能表现出明显的尺寸效应和组元依赖性，而晶体/晶体纳米金属多层膜体系呈现出与晶体/非晶体系截然不同的塑性变形力学和组织结构稳定性。最后，探讨了目前纳米金属多层膜相关研究存在的不足之处及其未来研究的主要方向。     

纳米技术稳定性研究取得重要进展

<正>金属晶粒细化至纳米尺寸可以大幅度提高其强度和硬度,但是由于引入了大量的晶界,纳米金属材料的结构稳定性变低,晶粒长大倾向明显。在一些纳米金属,如纯铜中,纳米晶粒甚至在室温条件下即发生长大。这种固有的不稳定性一方面给纳米金属     

IF钢晶体取向与纳米力学性能的原位分析

为了研究材料微区力学性能与多晶体取向之间的直接定量联系,以IF钢(无间隙原子钢)为例,分析了不同晶体取向与纳米力学性能之间的关系。首先利用高温激光扫描共聚焦显微镜(HLSM)对IF钢样品进行退火处理,以保证原位分析的有效性,然后通过电子背散射衍射(EBSD)对退火前后的标定区域进行晶体取向分析,得出晶体取向的原位变化规律,最后利用纳米压痕仪测试标定区域的微观力学性能。结果表明,不同晶体取向晶粒的杨氏模量不同,在原子间距较小的<111>晶体学方向上,杨氏模量值较高,在原子间距较大的<001>晶体学方向上,杨氏模量值较低,并通过理论计算验证了试验结果。退火后,不同晶体取向的晶粒硬度没有明显的规律性,但晶粒内位错密度显著降低,硬度比冷轧态明显下降,随着退火温度的升高,硬度降低速度变缓。     

硫化铜纳米晶体材料的研究进展

硫化铜纳米晶体材料具有纳米颗粒、纳米棒、纳米线、纳米管、纳米花等多种形态,拥有良好的光学、光电特性及催化能力,可以通过水热法、湿化学合成法、模板法、微波法等多种方法来合成。详细介绍了不同形态的硫化铜纳米晶体材料近年来在国内外的最新研究进展,最后指出了硫化铜纳米晶体材料的发展方向。     

过渡金属硼化物超硬材料的研究进展

过渡金属硼化物因其具有超硬特性而受到人们的关注,有望广泛应用于切屑加工工具、耐磨涂层、研磨材料等领域。介绍了制备过渡金属硼化物块体和薄膜材料的主要方法,并总结了部分过渡金属二元硼化物的结构和性能。不同过渡金属硼化物的结构不同,属于单斜、正交、六方等晶系;过渡金属硼化物薄膜材料的厚度在1μm以下;其硬度高于块体材料的硬度,达到超硬水平;但制得的过渡金属硼化物块体材料的硬度并不理想,与金刚石和立方氮化硼相比尚有一定的差距,还需进一步改进材料设计理念和探索新的制备方法。     

超声电化学法制备纳米金属及硫族半导体研究进展

超声电化学法将超声辅助辐照与电化学方法相结合,是超声化学和电化学的前沿研究领域之一,是合成纳米金属与硫族化合物材料的有效手段.该文从超声电化学原理与特点出发,总结近年来用超声电化学法合成纳米金属单质与纳米金属硫族半导体材料的研究进展.     

新型的MIMLC多层复合材料

MIMLC是高强度、高模量和低韧性的硬质材料(一般为陶瓷和难熔金属)与低强度、低模量而硬度低的高韧性材料(如纯金属、合金或高延性金属间化合物)层相互交替叠合而成的多层复合材料,其中的陶瓷或准熔金属层为高韧性材料提供了一种相互连贯的网络。这种复合材料通过改变各层的厚度即可获得符合要求的各种性能(包括硬度,强度,延性和断裂韧性)配合。 可用粉浆薄带浇注生产MIMLC。此法包括将粉末与适当粘结剂混合配成粉浆,然后浇注成带,经轧     

金属基玻璃粉末冶金材料的研究

本文采用粉末冶金方法制取金属—玻璃复合材料,并对其性能进行研究。结果表明,适量的玻璃添加物可以增加金属基体的强度和硬度,可以显著提高材料的减摩与耐磨性能。     

如何才能得到较准确的布氏硬度值

1前言工业生产中，金属材料或机械零件要求的布氏硬度值确定之后，用测量所得的布氏硬度值，即可判定材料是否满足技术要求。金属布氏硬度试验方法已有多年历史，随着国家标准和行业标准的制修订以及国际间的交流，现就被测试件如何才能得到较准确的布氏硬度值的一些问题进行探讨。2与布氏硬度值有关的一些技术要求仅列出布氏硬度值，其余力学性能指标略。2．l材料标准见表1。2．Zat艺标准见表2。2．3技术指标对比与分析1）45优质碳素结构同为冶金行业制修订的技术标准，但布氏硬度值要求不同。国际（GB）为＜197HBS，行业标准（YB／T）…     

合金元素V对Fe_3Al基纳米晶材料微观组织及力学性能的影响

通过铝热反应熔化法制备了合金元素V质量分数分别为5%、10%、15%的块体纳米晶Fe3Al材料。通过金相、XRD、SEM、TEM分析了其微观组织,研究了材料在室温压缩下的力学性能。经分析,V质量分数为5%和15%的Fe3Al纳米晶材料主要由无序bcc结构组成,未出现有序峰,而V质量分数10%的Fe3Al纳米晶材料由B2结构组成,出现(100)的有序峰;随着合金元素V质量分数的增加,材料的平均晶粒尺寸、维氏硬度、屈服强度和延伸率均先显著增大后显著减小;V质量分数10%的Fe3Al纳米晶材料的晶粒尺寸、硬度、屈服强度和延伸率为最大,分别为60 nm、359 HV、582 MPa和15.1%。     

Thin-layer nanocrystalline composite coatings: Production,structure, and properties

To obtain a nanocrystalline structural state of materials based on aluminum and titanium, high degrees of deformation are employed: rolling with considerable reduction; and shear under high pressure (5 GPa). The nanocrystalline materials obtained are used to create thin-layer composites, with nanocrystalline silicon between the uniform layers. Measurements show that the microhardness of the composites after the application of high pressure is 2.5 (for Al–Si) and 6 (for Ti–Si) times that of the initial material, while optimal practical properties are retained. The nanocrystalline composites obtained may be recommended for ultrahard thin-layer coatings on narrow or stressed local sections of components and for local corrosion protection.     

机械合金化纳米晶材料研究进展

综述了机械合金化制备纳米晶材料的研究进展，重点介绍了高强度铝合金，铜合金，难熔金属化合物，金属储氢材料，复相烯土永磁材料等几类机械合金化纳米晶材料的制备与组织性能，指出了机械合金化技术在纳米晶材料制备方面的优势及应用前景。     

A multi-scale grained microstructure of the surface nanocrystallized 304 stainless steel sheets after warm-rolling

An ultrafine grained microstructure was obtained for 304 stainless steel(304SS)sheets by using surface nanocrystallization and warm-rolling.The microstructure and mechanical properties were determined by X-ray diffraction(XRD),transmission electron microscope(TEM)and a test on microhardness.Experimental results were shown that the microstructure was featured by a continuous distribution from the nanocrystalline on the surface to micro-grains in the center,in which the volume fraction of the micro-sized grains is about 40% in the surface layer.This multi-scale grained microstructure was composed of austenite and martensite phases with a gradient increasing volume fraction of austenite from the surface to the centre.The microhardness of the resultant steel was higher than 150% of that as received,due to the refined grains and strain-induced martensitic transformation.The hardness distribution was consistent with the microstructural variation,suggesting a good combination of high strength and improved ductility.     

Effect of grain size on mechanical properties of nanocrystalline materials

The possibility of a dislocation mechanism in the deformation process of nanocrystalline materials is reviewed and analyzed. The present theoretical calculation, by taking the anisotropic characteristic of crystallographic symmetry and different choices of critical shear strength into account, results in a reasonable limit in grain size for applying dislocation pile-up theory to nanocrystalline materials. The deviation from the Hall—Petch relationship is rationalized in terms of a small number dislocation pile-up mechanism. A composite model is proposed to evaluate the strength of nanocrystalline materials. It is shown that this model can be used for interpreting the various cases observed in Hall—Petch studies. An analytical expression for assessing the creep rate of nanocrystalline materials by a diffusion mechanism, including triple line diffusion, is derived. It is predicted that the creep rate due to triple line diffusion will exhibit a stronger grain size dependence than that due to grain boundary diffusion.     

Formation and annealing behavior of nanocrystalline ferrite in Fe-0.89C spheroidite steel produced by ball milling

Nanocrystalline ferrite formation by ball milling in Fe-0.89C spheroidite steel and its annealing behavior have been studied through microstructure observations and microhardness measurements. It was found that at the early stage of ball milling, the dislocation density increases and dislocation cells form due to plastic deformation. At the middle stage of ball milling, a layered nanocrystalline structure forms near the surface of the powder by localized severe deformation. The microhardness of nanocrystalline ferrite (10 GPa) is much higher than that of work-hardened ferrite (4 GPa). Together with the nanocrystallization of ferrite, the dissolution of cementite was observed. At the final stage of ball milling, equiaxed nanocrystalline ferrite forms from layered nanocrystalline ferrite by increasing the local misorientation. By annealing the milled powders, recrystallization was observed in the workhardened ferrite region, while in the nanocrystalline ferrite region, a slow grain growth was observed instead of recrystallization.     

累积叠轧焊对退火态纯铝的显微组织和力学性能的研究

采用累积叠轧焊的方法对退火态的1060纯铝进行了累积叠轧实验,研究了累积叠轧次数对金属材料抗拉强度、延伸率、显微硬度、塑性的影响规律,通过透射电镜、拉伸及显微硬度实验分析了规律形成的原因。结果表明：经过多道次的轧制实验后,晶粒尺寸急剧细化,7道次后超细晶增多,晶粒最小细化到500nm。材料的抗拉强度和显微硬度也有显著提高。     

The structure and mechanical properties of metallic nanocrystals

Metallic nanocrystals are ultrafine-grained polycrystalline solids with grain sizes in the range of 1 to 10 nm in at least one dimension. Because of the extremely small dimensions, a large fraction of the atoms in these materials is located at the grain boundaries, and thus, they possess novel, and often improved, properties over those of conventional polycrystalline or glassy materials. In comparison to more conventional materials, nanocrystalline materials show a reduced density; increased thermal expansion, specific heat, and strength; a supermodulus effect; and extremely high diffusion rates. Traditionally brittle materials can be made ductile by nano-structure processing. At present, there is considerabe confusion on the nature of the micro-structure and mechanical properties of the nanocrystalline materials, especially of the equiaxed (three-dimensional, 3-D) type. The present article reviews the current understanding of nanocrystals and evaluates the data available on structure and mechanical properties of nanocrystalline metals. This invited overview is based on a presentation made in the symposium “Structure and Properties of Fine and Ultrafine Particles, Surfaces and Interfaces” presesnted as part of the 1989 Fall Meeting of TMS, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Structures Committee of ASM/MSD.     

Microstructure and tensile properties of compacted,mechanically alloyed,nanocrystalline Fe-AI

Data on mechanical properties of nanocrystalline materials have been limited, due in part to the difficulty in producing consolidated nanocrystalline materials of sufficient quantity for characterization and evaluation. A second problem is consolidation and retention of the nanostructure. A vacuum hot-pressing consolidation program has been developed to produce full-dense compacts from attrition milled, mechanically alloyed, nanograin micron-size particles of Fe-2 wt pet Al powder. The resulting compacts were of sufficient size to allow evaluation of microstructure, density, hardness, and tensile properties. The compacted microstructure was a composite of pure iron submicrograins and Fe-A1 nanograin clusters. Tensile strength was found to be proportional to the sample’s density squared. For full-dense compacts, tensile strength of nanocrystalline compacts approaching 1 GPa was obtained.     

Influence of cold rolling and annealing on the microstructure,mechanical properties,and electrical conductivity of an artificial microcomposite Cu-18% Nb alloy

The influence of cold rolling and subsequent annealing at different temperatures on the micro-structure, strength properties, and electrical conductivity of a microcomposite Cu-18% Nb alloy fabricated by bundling and deformation is studied. A composite billet is rolled up to a total true strain of 3.5 and 5.1. After rolling, a nanocrystalline structure is obtained with an average filament width of 70–100 nm depending on the rolling strain. The ultimate tensile strength of the rolled foils is 867–934 MPa and the electrical conductivity is 19–40% of the pure copper conductivity. It is shown that annealing at 550°C results in an increase in the conductivity from 40 to 60% at a retained strength (microhardness) of the alloy.     

Characterization of Strain-Rate Sensitivity and Grain Boundary Structure in Nanocrystalline Gold-Copper Alloys

The power-law dependence of strength on strain rate provides a measure of the strain-rate sensitivity. In general, strength increases as grain size decreases from the microscale into the nanoscale regime for many cubic metals. The method of microscratch testing is used to measure microhardness in order to evaluate material strength. The strain-rate dependence of hardness is measured by varying the microscratch velocity. New results for nanocrystalline gold alloys show that the exponent (m) of the power-law dependence of stress on strain rate increases to 0.20 as grain size decreases to values less than 10 nm. A high-resolution electron microscopy examination of grain boundary structure reveals that an increase in the strain-rate sensitivity exponent (m) is found with an increase in the grain boundary misorientation.