Developing SPD methods for processing bulk nanostructured materials with enhanced properties

Severe plastic deformation (SPD), i.e. intense plastic straining under high pressure, is an innovative technique for processing ultrafine-grained nanostructured metals and alloys. SPD fabricated nanostructures can lead to novel properties, which, however, depend strongly on the processing parameters. This paper focuses on examples of attaining enhanced mechanical properties in several metals and alloys, subjected to severe plastic deformation. In addition, the relationships among the processing conditions, microstructures and properties of the materials produced by SPD are considered.     

The use of severe plastic deformation techniques in grain refinement

Severe plastic deformation (SPD) has emerged as a promising method to produce ultrafine-grained materials with attractive properties. Today, SPD techniques are rapidly developing and are on the verge of moving from lab-scale research into commercial production. This paper discusses new trends in the development of SPD techniques suchas high-pressure torsion and equal-channel angle pressing, as well as new alternative techniques for introducing SPD. The paper also contains a comparative analysis of SPD techniques in terms of their relative capabilities for grain refinement, enhancement of properties, and potential to economically produce ultrafine-grained metals and alloys. For more information, contact Terry C. Lowe, Science and Technology Base Programs, Los Alamos National Laboratory, Los Alamos, NM 87545; (505) 667-7824; fax (505) 665-3199; e-mail tlowe@lanl.gov.     

The fundamentals of nanostructured materials processed by severe plastic deformation

Nanostructured materials produced by severe plastic deformation (SPD) are 100% dense, contamination-free, and sufficiently large for use in real commercial structural applications. These materials are found to have high strength, good ductility, superior superplasticity, a low friction coefficient, high wear resistance, enhanced high-cycle fatigue life, and good corrosion resistance. This article reviews the structures and properties of nanostructured materials produced by SPD and reports recent progress in determining the deformation mechanisms that lead to these superior mechanical properties. For more information, contact Yuntian T. Zhu, Los Alamos National Laboratory, Materials Science and Technology Division, Los Alamos, NM 87545; (505) 667-4029; fax (505) 667-2264; e-mail yzhu@lanl.gov.     

大体积超细晶金属材料的剧烈塑性变形法制备技术

介绍了大体积超细晶金属材料的各种常见剧烈塑性变形法制备技术,系统阐述了各种制备技术的基本原理,并分析比较了这些制备技术的优缺点和适用范围,指出了剧烈塑性变形法制备技术的发展方向。     

Severe plastic deformation (SPD) processes for metals

Processes of severe plastic deformation (SPD) are defined as metal forming processes in which a very large plastic strain is imposed on a bulk process in order to make an ultra-fine grained metal. The objective of the SPD processes for creating ultra-fine grained metal is to produce lightweight parts by using high strength metal for the safety and reliability of micro-parts and for environmental harmony. In this keynote paper, the fabrication process of equal channel angular pressing (ECAP), accumulative roll-bonding (ARB), high pressure torsion (HPT), and others are introduced, and the properties of metals processed by the SPD processes are shown. Moreover, the combined processes developed recently are also explained. Finally, the applications of the ultra-fine grained (UFG) metals are discussed.     

Microstructural characterization of SPD processed materials

The results of a detailed microstructural characterization of bulk SPD processed nanostructured materials, and their interpretations obtained by application of the modem techniques of structural analysis are presented. It is shown that the application of advanced X-ray methods as well as TEM investigations results in evaluation of rather comprehensive information on the microstructure of SPD materials. This information includes values of the crystal lattice parameter, coherently scattering domain size, elastic microdistortions, atomic displacements, crystallographic texture, etc.     

Recent development in reactive synthesis of nanostructured bulk materials by spark plasma sintering

As a relatively novel sintering technique, spark plasma sintering (SPS) has been used extensively over the past decade to prepare a wide variety of materials, e.g., ceramics, composites, cermets, metals and alloys. Many applications of the SPS technique are the fabrication of nanostructured materials using nanosize powdered precursors as starting materials. This article provides a review of research activities that concentrate on the development of the SPS reaction sintering (SPS-RS) to produce dense nanostructured materials, which indicate that it is possible to synthesize and compact dense bulk materials with controlled sub-micron or even nanoscale grain sizes by the use of the SPS technique.     

Surface nanocrystallisation engineering: scientific and industrial potential

Abstract

By means of surface mechanical attrition treatment (SMAT), a nanostructured surface layer with a graded grain size distribution ranging from nano-to micrometres can be synthesised on various metallic materials. In this paper, the grain refinement mechanism, mechanical and diffusion properties, and chemical reactivity of the nanostructured surface layer, are reviewed. In addition, effects of the nanostructured surface layer on the mechanical performance and surface thermochemical treatment processes of engineering materials are described. Previous investigations have indicated that the nanostructured surface layer synthesised by means of SMAT on metallic materials provides many unique opportunities in both basic scientific research and technological applications.     

Spark plasma sintering for multi-scale surface engineering of materials

Recently, significant progress has been made in understanding the effect of multi-scale microstructural features, including nano-, micro-, and macro-features, on the properties of materials. Controlling the length scale of micro-structural features provides tremendous opportunities for enhancing the properties of materials, including extraordinary strength and hardness, unprecedented damage from tribological contacts, and improvements in a number of functional properties of the materials. Spark plasma sintering (SPS) process which combines the effects of uniaxial pressure and pulsed direct current is becoming increasingly important for the processing of bulk shapes of amorphous and nanostructured materials. These materials can also be good candidates for high-performance coatings. This article presents a review of our ongoing efforts to use SPS to produce engineered coatings of amorphous and nanostructured materials for various applications, including structural, tribological, and biomedical applications.     

Influence of the notch root radius on the fracture toughness of brittle metals: Nanostructure tungsten alloy,a case study

Tungsten and tungsten-based alloys are considered to be candidate materials for next-generation nuclear fusion reactors. Unfortunately, their use in structural applications is compromised due to their inherent brittleness. To improve this crucial feature, it is necessary to accurately measure their fracture toughness as a real property independent of geometrical parameters and the method used to introduce the induced crack. This goal is the objective of this work; where the notch tip radius influence on the fracture toughness of a brittle nanostructured tungsten alloy is analyzed in depth.Three-point bending tests at room temperature were performed on four types of notch geometries in which the notch root radius was gradually reduced. The notches were introduced using four different methods: with a classical diamond disc, a diamond wire, a razor blade and an ultra-short pulsed laser. The results showed that single edge notched beam specimens overestimate the fracture toughness values and introduce some deformation into the notch root grains. However, the razor blade yields very good results with a low dispersion, but is only suitable for coarse grain materials since the size effect appears as the grain size decreases. Therefore, for nanostructured materials such as in this case, the notch root radius is still too large (several times the grain size), requiring the implementation of a new method. Very sharp single edge laser-notched beam specimens with a 5–20 nm root radius were accordingly produced by using ultra-short pulsed laser ablation. This method has been previously used on ceramics but no evidence of its use was found on metals.     

Emerging Science and Research Opportunities for Metals and Metallic Nanostructures

During the next decade, fundamental research on metals and metallic nanostructures (MMNs) has the potential to continue transforming metals science into innovative materials, devices, and systems. A workshop to identify emerging and potentially transformative research areas in MMNs was held June 13 and 14, 2012, at the University of California Santa Barbara. There were 47 attendees at the workshop (listed in the Acknowledgements section), representing a broad range of academic institutions, industry, and government laboratories. The metals and metallic nanostructures (MMNs) workshop aimed to identify significant research trends, scientific fundamentals, and recent breakthroughs that can enable new or enhanced MMN performance, either alone or in a more complex materials system, for a wide range of applications. Additionally, the role that MMN research can play in high-priority research and development (R&D) areas such as the U.S. Materials Genome Initiative, the National Nanotechnology Initiative, the Advanced Manufacturing Initiative, and other similar initiatives that exist internationally was assessed. The workshop also addressed critical issues related to materials research instrumentation and the cyberinfrastructure for materials science research and education, as well as science, technology, engineering, and mathematics (STEM) workforce development, with emphasis on the United States but with an appreciation that similar challenges and opportunities for the materials community exist internationally. A central theme of the workshop was that research in MMNs has provided and will continue to provide societal benefits through the integration of experiment, theory, and simulation to link atomistic, nanoscale, microscale, and mesoscale phenomena across time scales for an ever-widening range of applications. Within this overarching theme, the workshop participants identified emerging research opportunities that are categorized and described in more detail in the following sections in terms of the following: three-dimensional (3-D) and four-dimensional (4-D) materials science. Structure evolution and the challenge of heterogeneous and multicomponent systems. The science base for property prediction across the length scales. Nanoscale phenomena at surfaces—experiment, theory, and simulation. Prediction and control of the morphology, microstructure, and properties of “bulk” nanostructured metals. Functionality and control of materials far from equilibrium. Hybrid and multifunctional materials assemblies. Materials discovery and design: enhancing the theory-simulation-experiment loop. Following an introduction, these emerging research opportunities are discussed in detail, along with challenges and opportunities for the materials community in the areas of instrumentation, cyberinfrastructure, education, and workforce development.     

Materials applications of photoelectron emission microscopy

Photoelectron emission microscopy (PEEM) is a versatile technique that can image a variety of materials including metals, semiconductors and even insulators. Under favorable conditions the most advanced aberration corrected instruments have a spatial resolution approaching 2 nm. Although PEEM cannot compete with transmission or scanning electron microscopies for ultimate resolution, the technique is much gentler and has the unique advantage of imaging structure as well as electronic and magnetic states on the nanoscale. Since the image contrast is derived from spatial variations in electron photoemission intensity, PEEM is ideal for interrogating both static and dynamic electronic properties of complex nanostructured materials. Here, we review the key principles and contrast mechanisms of PEEM and briefly summarize materials applications of PEEM.     

强烈塑性变形表面纳米化的研究现状

强烈塑性变形表面纳米化(SPD-SNC)技术是近几年才开始备受人们广泛关注的新技术,它不仅为研究形变诱发的纳米化过程和宽尺寸范围内(从微米到纳米量级)结构与性能的关系提供思路,制备理想样品;而且将纳米材料的优异性能应用于改造传统工程材料,显著地提高金属材料的性能,可望在工业上获得实际应用.从SPD-SNC的方法、机理、组织结构和性能等方面总结了该技术近年来取得的进展和存在的问题,指出了今后的研究发展方向.     

Severe Plastic Deformation Techniques for Bulk Ultrafine-grained Materials

剧烈塑性变形制备超细晶金属材料是当前的研究热点。基于机制和微观组织变化综述了剧烈塑性变形制备块状超细晶材料的一些方法,特别是给出了两种新型成形技术-等截面椭圆变通道扭挤和等截面椭圆转变通道扭拉,此外还阐述了剧烈塑性变形存在的问题及未来的研究方向。     

Nanostructured component fabrication by electron beam-physical vapor deposition

Fabrication of cost-effective, nano-grained net-shaped components has brought considerable interest to Department of Defense, National Aeronautics and Space Administration, and Department of Energy. The objective of this paper is to demonstrate the versatility of electron beam-physical vapor deposition (EB-PVD) technology in engineering new nanostructured materials with controlled microstructure and microchemistry in the form of coatings and net-shaped components for many applications including the space, turbine, optical, biomedical, and auto industries. Coatings are often applied on components to extent their performance and life under severe environmental conditions including thermal, corrosion, wear, and oxidation. Performance and properties of the coatings depend upon their composition, microstructure, and deposition condition. Simultaneous co-evaporation of multiple ingots of different compositions in the high energy EB-PVD chamber has brought considerable interest in the architecture of functional graded coatings, nano-laminated coatings, and design of new structural materials that could not be produced economically by conventional methods. In addition, high evaporation and condensate rates allowed fabricating precision net-shaped components with nanograined microstructure for various applications. Using EB-PVD, nano-grained rhenium (Re) coatings and net-shaped components with tailored microstructure and properties were fabricated in the form of tubes, plates, and Re-coated spherical graphite cores. This paper will also present the results of various metallic and ceramic coatings including chromium, titanium carbide (TiC), titanium diboride (TiB₂), hafnium nitride (HfN), titanium-boron-carbonitride (TiBCN), and partially yttria stabilized zirconia (YSZ) TBC coatings deposited by EB-PVD for various applications. This paper was presented at the International Symposium on Manufacturing, Properties, and Applications of Nanocrystalline Materials sponsored by the ASM International Nanotechnology Task Force and TMS Powder Materials Committee, October 18–20, 2004, Columbus, OH.     

快速凝固制造贵金属微细粉末

研究了快速凝固高压气体雾化和离心雾化组合制粉设备和技术及其在贵金属微细粉末、电工合金、电子浆料、钎料中的应用,与传统的电解法化学共沉淀法生产银粉和银基电工材料比较,结果表明快速凝固粉末微细有效地扩大了合金元素的固溶度,并具有优异的综合性能。加工工艺中贵金属损耗小、效率高、生产成本低、无环境污染等。因此,利用该技术不仅开发出新材料,而且在改善传统材料性能的同时为规模化生产开辟新途径。     

Preface

The S2P(Semi-Solid Processing of Alloys and Composites) International Conferences are dedicated to science and technology of semi-solid processing of metals. Since the discovery of the specific flow     

Electron Beam Applications to Refractory Metals

A relatively new metallurgical tool—the electron beam— is opening new routes for the production, fabrication, and testing of refractory metals. This article discusses various applications of the electron beam heat source to these metals.