Nanostructured Composite Materials with Improved Deformation Behavior

The recent progress in the development of nanostructured composites is described for Zr‐base multicomponent alloys as a typical example for such materials. These advanced composite materials are attractive candidates for structural as well as functional applications. The combination of high strength with high elastic strain of fully nanocrystalline and glassy alloys renders them quite unique in comparison to conventional (micro‐)crystalline materials. However, one major drawback for their use in engineering applications is the often limited macroscopic plastic deformability, despite the fact that some of these alloys show perfectly elastic‐plastic deformation behavior. To improve the room temperature ductility of either fully nanocrystalline or amorphous alloys, the concept of developing a heterogeneous microstructure combining a glassy or nanostructured matrix with second‐phase particles with a different length‐scale, has recently been employed. This review describes the composition dependent metastable phase formation in the Zr‐(Ti/Nb)‐Cu‐Ni‐Al alloy system, which in turn alters the mechanical properties of the alloys. We emphasize the possibilities to manipulate such composite microstructures in favor of either strength or ductility, or a combination of both, and also discuss the acquired ability to synthesize such in‐situ high‐strength composite microstructures in bulk form through inexpensive processing routes.     

Anisotropic Magnetoresistance Effect in Amorphous and Nanocrystalline Fe(Cu,Nb)-Si-B Alloys

1. IntroductionRecent works on the properties of Fe-basednanocrystalline alloys have generated considerable interest in the filed of materials because of their excellent soft magnetic characteristi.s[1'21. As a newlydeveloped material, the origin of the excellent softmagnetic characteristics was not clear yet. H..z.r[3]et al. have suggested that smaller magnetic crystallineanisotropy is one of the most important factors whichdominate the excellent soft magnetic characteristics,but the explanat…     

Influence of Annealing Conditions on Nanocrystalline and Ultra-Soft Magnetic Properties of Fe75.5Cu1Nb1Si13.5B9 Alloy

The magnetic and structural properties of FINEMET alloy with a composition of Fe75.5Cu1Nb1Si13.5B9 were investigated after primary and secondary crystallization of amorphous ribbon sample.The crystallization behavior and the nanocrystal formation of the samples were performed by differential thermal analysis(DTA) which in turn was supported by X-ray diffraction(XRD) study.Temperature dependence of initial permeability of amorphous and devitrified toroid shaped samples has been measured.Enhancement of Curie temperature of the amorphous alloy has been observed due to the irreversible structural relaxation.With the appearance of nanocrystalline phase the Curie temperature of the residual amorphous phase gradually decrease with the increase of annealing temperature.Their temperature dependence reflects the characteristic annealing temperature evolution of the basic magnetic parameters in these nanocrystalline systems.Saturation magnetization,Ms,increases with annealing temperature Ta for the samples and finally decreases during annealing at a temperature much higher than peak crystallization temperature.     

Hopkinson Effect in Soft Magnetic Materials

1. IntroductionIt is well known that the initial permeability ofmany ferromagnetic materials increases with increasing temperature and appears a sharp peak just before the Curie point, and then drops off to a verysmall value. The peak is called the Hopkinson peakand the phenomenon is normally called the Hopkinson effectll]. Since this effect is valid for all the ferromagnetic materials, it has been used as a methodto measure the Curie temperature. However, in ourresearch work of nanocrystall…     

Nanostructured interfaces for enhancing mechanical properties of composites: Computational micromechanical studies

Computational micromechanical studies of the effect of nanostructuring and nanoengineering of interfaces, phase and grain boundaries of materials on the mechanical properties and strength of materials and the potential of interface nanostructuring to enhance the materials properties are reviewed. Several groups of materials (composites, nanocomposites, nanocrystalline metals, wood) are considered with view on the effect of nanostructured interfaces on their properties. The structures of various nanostructured interfaces (protein structures and mineral bridges in biopolymers in nacre and microfibrils in wood; pores, interphases and nanoparticles in fiber/matrix interfaces of polymer fiber reinforced composites and nanocomposites; dislocations and precipitates in grain boundaries of nanocrystalline metals) and the methods of their modeling are discussed. It is concluded that nanostructuring of interfaces and phase boundaries is a powerful tool for controlling the material deformation and strength behavior, and allows to enhance the mechanical properties and strength of the materials. Heterogeneous interfaces, with low stiffness leading to the localization of deformation, and nanoreinforcements oriented normally to the main reinforcing elements can ensure the highest damage resistance of materials.     

MATERIAL PROCESSING VIA AN INTEGRATED MECHANICAL AND THERMAL ACTIVATION PROCESS

This paper reviews the recent progress in material synthesis and processing based on mechanical activation approaches. Material processing based on mechanical alloying and attrition has been widely used to prepare metastable phases, amorphous alloys, composites, and nanostructured materials. The most recent progress made in mechanical activation is the development of a new process that integrates mechanical activation and thermal activation to produce novel materials as well as conventional materials. The integrated mechanical and thermal activation (IMTA) process represents one of the most exciting recent advancements and holds great promise for commercial viability. Examples of enhanced reaction rates and synthesis of nanocrystalline materials are provided to illustrate the progress brought about by the IMTA process.     

Structure and properties of nanocrystalline materials

The present article reviews the current status of research and development on the structure and properties of nanocrystalline materials. Nanocrystalline materials are polycrystalline materials with grain sizes of up to about 100 nm. Because of the extremely small dimensions, a large fraction of the atoms in these materials is located at the grain boundaries, and this confers special attributes. Nanocrystalline materials can be prepared by inert gas-condensation, mechanical alloying, plasma deposition, spray conversion processing, and many other methods. These have been briefly reviewed. A clear picture of the structure of nanocrystalline materials is emerging only now. Whereas the earlier studies reasoned out that the structure of grain boundaries in nanocrystalline materials was quite different from that in coarse-grained materials, recent studies using spectroscopy, high-resolution electron microscopy, and computer simulation techniques showed unambiguously that the structure of the grain boundaries is the same in both nanocrystalline and coarse-grained materials. A critical analysis of this aspect and grain growth is presented. The properties of nanocrystalline materials are very often superior to those of conventional polycrystalline coarse-grained materials. Nanocrystalline materials exhibit increased strength/hardness, enhanced diffusivity, improved ductility/toughness, reduced density, reduced elastic modulus, higher electrical resistivity, increased specific heat, higher thermal expansion coefficient, lower thermal conductivity, and superior soft magnetic properties in comparison to conventional coarse-grained materials. Recent results on these properties, with special emphasis on mechanical properties, have been discussed. New concepts of nanocomposites and nanoglasses are also being investigated with special emphasis on ceramic composites to increase their strength and toughness. Even though no components made of nanocrystalline materials are in use in any application now, there appears to be a great potential for applications in the near future. The extensive investigations in recent years on structure-property correlations in nanocrystalline materials have begun to unravel the complexities of these materials, and paved the way for successful exploitation of the alloy design principles to synthesize better materials than hitherto available.     

Magnetothermal Analysis of Nanocrystallization of Amorphous and Relaxations of Nanocrystalline Materials

For a few years it has been realized that nanocrystalline phases can be formed during crystallization of amorphous alloys annealed isothermally below the crystallization temperature of usual heating experiments. Data of this transformation monitored by the measurement of magnetic susceptibility are presented. A method using a magnetic balance with electronic stabilisation and combined computer facilities is applied. Constant heating and cooling rates as well as isothermal heat treatments are used. Magnetic measurements are able to detect the onset of the transformation of amorphous Ni-P alloys much earlier than was possible with differential scanning calorimetry. The transformation kinetics can be analyzed by means of the Avrami plot based on the Johnson-Mehl-Avrami equation.The kinetics of solid state reactions in the nanostructured material can be investigated similarly. Formation of a Ni-phase in a nanostructured Hf-Ni alloy could be detected in a very early stage, where calorimetric methods are not sensitive. Segregation phenomena could be detected from the experiments even after long time. The sensitivity of the applied method is not dependent on the heating rate as the sensitivity of scanning calorimetry is     

Novel In Situ Nanostructure-Dendrite Composites in Zr-Base Multicomponent Alloy System

The evolution of a nanostructure-dendrite composite microstructure of two Zr-base alloys solidified through different casting routes is presented. The alloys were designed by adding different amounts of Nb to the Zr-based multicomponent glass-forming alloy system. The refractory metal Nb promotes the formation of a primary phase having dendritic morphology, whereas the residual melt solidifies to a nanostructured/amorphous matrix. The volume fraction and the morphology of the dendritic phase varied with the Nb content and the adopted casting route. A correlation between the alloy composition and adopted casting method with evolved microstructures and mechanical properties is revealed. These composites exhibit a unique combination of high fracture strength up to 1922 Mpa, as well as plastic strain over 15.8% under uniaxial compression testing at room temperature. The high strength of these composites is imparted by the nanostructured matrix, whereas the large plastic strain is a consequence of the retardation of excessive localized shear banding in the matrix by ductile dendrites. The significant work hardening of the composites prior to fracture is attributed to dislocation multiplication in the solid solution-strengthened dendritic phase.     

Nanostructured electronic and magnetic materials

Research and development in nanostructured materials is one of the most intensely studied areas in science. As a result of concerted R & D efforts, nanostructured electronic and magnetic materials have achieved commercial success. Specific examples of novel industrially important nanostructured electronic and magnetic materials are provided. Advantages of nanocrystalline magnetic materials in the context of both materials and devices are discussed. Several high technology examples of the use of nanostructured magnetic materials are presented. Methods of processing nanostructured materials are described and the examples of sol gel, rapid solidification and powder injection moulding as potential processing methods for making nanostructured materials are outlined. Some opportunities and challenges are discussed.     

Mikrostruktur und Eigenschaften lichtbogengespritzter Schichten auf Eisenbasis

Microstructure and properties of Fe‐based wire arc sprayed coatings Innovative iron based feedstocks for wire arc spraying are a promising alternative for conventional carbide reinforced feedstocks for wear applications. Recently the main area of research is focused on improving the properties of deposited functional coatings by varying the wire composition. The influence on the crystalline structure and the dimension of the hard phases in the resulting microstructure is of particular interest in this context. The objective of the investigation is to produce coatings with an amorphous phase, submicron and nanocrystalline structure. The forming of the amorphous phase is influenced by high cooling rates of the molten and partly molten particles impinging on the substrate. Thus, the achieved coatings are characterized by high hardness as well as high corrosion and wear resistance. The present paper introduces iron based coatings produced by wire arc spraying. Due to the application of cored wires with a modified alloy composition the forming of an amorphous phase as well as a submicron‐ and nanocrystalline structure is promoted. The filling of the cored wires are based on FeB with a eutectic composition and is varied by adding Cr₃C₂, FeSi, FeCrC and AlMg. The adding of further elements like Cr, C, Si, Al and Mg should improve the forming of the amorphous phase. The deposited coatings are analyzed regarding to the resulting coating properties and phase composition in connection with the composition of the cored wires. XRD‐analysis’ proved that the Fe‐based coatings contain an amorphous phase.     

高性能软磁合金的研究进展EI北大核心CSCD

软磁材料是一种极为重要且应用十分广泛的能源材料,近年来,随着磁性元件的日益高频化和小型化,以及节能环保的号召,开发和研究高性能软磁材料具有重要意义。本工作概述了软磁合金的发展历史,重点归纳出各类软磁合金(包括传统软磁合金、非晶/纳米晶软磁合金、高熵软磁合金)的成分、微观组织、磁性能以及应用范围,并总结出不同软磁合金的优、缺点;指出典型合金的微观组织对合金软磁性能(尤其矫顽力)具有关键性的主导作用,进而探讨了影响软磁合金矫顽力的因素及其微观机制,发现控制晶粒尺寸(或纳米粒子尺寸)是获得低矫顽力的关键,并描述了矫顽力的微观影响机制在高熵软磁合金中的发展;最后,展望了高熵软磁合金因多主元混合的成分特性带来的组织多样化,更有利于实现对合金性能的调控,并有望作为新一代高温软磁体材料。     

Dependence of Structure and Magnetic Properties on Annealing Temperature in Fe72.5Cu1Nb2V2Si13.5B9 Alloy

The magnetic properties of Fe72.5 Cu1Nb2V2Si13.5B9 alloy are investigated from an amorphous to a nanocrystalline and complete crystalline state.The sample annealed at 550℃ for 0.5h shows a homogeneous nanocrystalline structure and presents excellent soft magnetic properties.When the specimens were annealed at a temperature above 600℃,the magnetic properties are obviously deteriorated because the grain size grows up,exceeding the exchange length.     

Nanostructural materials formation by mechanical alloying: Morphologic analysis based on transmission and scanning electron microscopic observations

The development of nanostructured materials offers new scientific and technological perspectives due to the specific interesting physical properties of these materials. These properties derive either from their reduced grain size or from the structure and properties of the grain boundaries, which constitute a significant volume fraction. Mechanical alloying, widely used to produce dispersion-strengthened and amorphous alloys, has been employed in recent years to synthesize nanocrystalline metallic, semiconductors, and covalent component-based materials. Based on statistical analysis of transmission and scanning electron microscopic images, the distribution and spatial repartition of the nanostructural material prepared by mechanical alloying and/or attrition are presented for some specific cases.     

Isothermal nanocrystallisation behaviour of melt spun Al86Ni9 Mm5 (Mmmischmetal)amorphous alloy

Abstract

The structure and mechanical properties of melt spun Al₈₆Ni₉Mm₅ alloy ribbons in both as solidified amorphous and heat treated nanocomposite conditions were investigated using DSC, XRD, TEM, and Vickers microhardness techniques. Primary crystallisation of the amorphous alloy resulted in the formation of fine nanocrystalline fcc-Al particles embedded in an amorphous matrix forming a nanocomposite. The growth behaviour of the primary fcc-Al particles under isothermal conditions was investigated. The hardness ofthe composite varied with the solute content in the amorphous phase and the microstructure after heat treatment. The hardening in these nanocomposites was quantitatively explained using a rule of mixtures model based on the volume fraction of the amorphous matrix and the Al particles. The nanometre sized particles were treated as perfect materials and the matrix was treated as an amorphousmaterial, in which the solute concentration increased as the volume fraction of the Al particles increased. The calculated results for the heat treated specimens using the rule of mixtures based on the isostress model have been found to be in good agreement with the experimentally obtained results.     

Preparation and characterization of rare-earth bulks with controllable nanostructures

The preparation and characterization of pure rare-earth-metal bulks with controllable nanostructures are reported in this paper. A novel 'oxygen-free' in?situ synthesis technique that combines inert-gas condensation with spark plasma sintering (SPS) technology is proposed. Taking into account the special mechanisms of SPS consolidation and the scale effects of nanoparticles, we introduced practical procedures for preparing rare-earth bulks of amorphous, mixed amorphous and nanocrystals, and nanocrystalline microstructures, respectively. Compared with the conventional polycrystalline bulk, these nanostructured bulks exhibit substantially improved physical and mechanical properties. This technique enables comprehensive studies on the microstructures and properties of a large variety of nanostructured metallic materials that are highly reactive in the air.     

基于分子动力学模拟的铜锆晶体/非晶双相纳米复合材料力学行为

金属玻璃因其较差的室温塑性限制了其广泛应用,因此提升金属玻璃的力学性能、探明金属玻璃的变形机制已经成为当前材料领域的研究热点。采用分子动力学方法研究了晶粒尺寸和分布对晶体/非晶B2-CuZr/CuZr双相复合材料力学行为的影响。研究结果表明,随着纳米晶粒的尺寸增大,复合材料变形模式发生了从相对均匀变形到单一剪切带的局部变形的转变。研究指出,增大纳米晶粒尺寸/体积分数能有效提高复合材料的峰值应力,但除了较小尺寸纳米晶粒模型外,双相复合材料的塑性没有明显增强。此外,相对于交叉排列,纳米晶粒的对齐排列导致了更严重的塑性应变局部化。本文的研究结果对于设计和制备高性能的金属玻璃材料具有重要的参考价值和指导意义。      

Experimental and modeling studies on phase stability of nanocrystalline magnetic Sm2Co7

In contrast to the conventional polycrystalline low-Co Sm–Co alloys that have very weak permanent magnetic properties, the Sm₂Co₇ alloy has been found to have fairly promising permanent magnetic performance when its grain size is reduced to the nanoscale. It was discovered that the crystal structure of the nanocrystalline Sm₂Co₇ has a strong nanograin-size-dependent stability. The rhombohedral structure of Sm₂Co₇ phase which is metastable at temperatures lower than 1435 K in conventional polycrystalline system can exist stably at room temperature in the nanocrystalline system. To understand the phase stability of the nanocrystalline Sm₂Co₇, the experimental and nanothermodynamic analyses were combined to describe quantitatively the phase transformation behavior of Sm₂Co₇ on the nanoscale. The results are important for the development of nanostructured Sm–Co permanent magnets.     

Nonlinear microstructural constitutive equation of nanocrystalline metals

Summary. Based on experimental observations, nanocrystalline materials are modeled as composite systems in which the amorphous interfacial phase is treated as the matrix, whereas the nano-scale single crystals are modeled as inclusions. Generally speaking, the elastic moduli of nanoscale crystals are higher than those of the amorphous matrix phase, and the deformation mechanism of nanocrystalline materials depends heavily on the size of the crystals. For conventional macro size crystal materials, such as coarse-grained polycrystalline materials, the deformation mechanism due to dislocation movement is dominant. When the crystal size is reduced to a certain critical value, plastic deformation is caused by shear banding in the amorphous matrix. In order to model such a deformation mechanism in nanocrystalline materials, constitutive equations are established based on internal variable theory. The proposed model reveals the relation between the yield strength and the grain size of the material.     

镁合金及其复合材料电磁屏蔽性能研究进展

航空航天、信息通信等领域不断发展,随之产生的电磁干扰也逐渐被人们重视,面对电磁屏蔽材料兼顾结构轻量化的功能/结构一体化发展趋势,已经有越来越多的研究者将关注点放在了镁合金及其复合材料上。镁合金作为一种密度极低的金属材料,具有较高的比强度和比刚度、优异的阻尼和电磁屏蔽性能,以镁合金为基体制备复合材料可进一步提升材料的综合性能,兼具高导电性、导热性和优异力学性能的碳纳米管（CNTs）、纳米石墨烯（GNPs）等纳米碳基材料和具有特殊空心结构的粉煤灰球（FACs）均可作为镁合金复合材料的增强体,综合提升材料的力学和电磁屏蔽性能。目前,针对镁合金及其复合材料的电磁屏蔽性能研究主要集中于合金化元素选择及成分设计、热处理及加工工艺、晶粒尺寸、织构及相分布、复合材料体系设计等方面。从电磁屏蔽原理出发,综述了近年来镁合金及其复合材料电磁屏蔽性能的研究,主要对镁合金及其复合材料导电、导磁性的影响因素进行了介绍,并讨论了作为复合材料提升镁合金电磁屏蔽性能的机理,最后针对这类轻量化电磁屏蔽结构材料的应用前景进行了展望。