Twenty-five years of ultrafine-grained materials: achieving exceptional properties through grain refinement
TL;DR: In this article, an overview of the more recent developments in this field, with special emphasis on the opportunities for achieving homogeneity in the as-processed materials and on the general characteristics of the mechanical properties achieved after SPD processing.
About: This article is published in Acta Materialia.The article was published on 2013-11-01. It has received 614 citations till now.
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TL;DR: A heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse- grained metal.
Abstract: Grain refinement can make conventional metals several times stronger, but this comes at dramatic loss of ductility. Here we report a heterogeneous lamella structure in Ti produced by asymmetric rolling and partial recrystallization that can produce an unprecedented property combination: as strong as ultrafine-grained metal and at the same time as ductile as conventional coarse-grained metal. It also has higher strain hardening than coarse-grained Ti, which was hitherto believed impossible. The heterogeneous lamella structure is characterized with soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix. The unusual high strength is obtained with the assistance of high back stress developed from heterogeneous yielding, whereas the high ductility is attributed to back-stress hardening and dislocation hardening. The process discovered here is amenable to large-scale industrial production at low cost, and might be applicable to other metal systems.
1,063 citations
TL;DR: In this article, the authors present an overview of experimental data and theoretical concepts addressing the unique combination of superior strength and enhanced ductility of metallic nanomaterials, and consider the basic approaches and methods for simultaneously optimizing their strength and ductility, employing principal deformation mechanisms, crystallographic texture, chemical composition as well as second-phase nano-precipitates, carbon nanotubes and graphene.
573 citations
Cites background from "Twenty-five years of ultrafine-grai..."
...Concerning the testing conditions, it is well known [171,280,281] that under certain temperature and strain rate conditions, NS materials can display enhanced ductility and even exhibit superplasticity, i....
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...The superplasticity of NS materials has been discussed in several recent reviews [281,282]....
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...[170,288] (see also recent reviews on nanoSPD history) [281,289] and to date the SPD processing has become a major approach for producing metals with ultrafine and nanosized grains [47,281]....
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15 Jan 2016-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors reviewed the findings of Bridgman and his successors from 1935 to 1988 using the HPT method and summarized their historical importance in recent advancement of materials, properties, phase transformations and HPT machine designs.
Abstract: High-pressure torsion (HPT) method currently receives much attention as a severe plastic deformation (SPD) technique mainly because of the reports of Prof. Ruslan Z. Valiev and his co-workers in 1988. They reported the efficiency of the method in creating ultrafine-grained (UFG) structures with predominantly high-angle grain boundaries, which started the new age of nanoSPD materials with novel properties. The HPT method was first introduced by Prof. Percy W. Bridgman in 1935. Bridgman pioneered application of high torsional shearing stress combined with high hydrostatic pressure to many different kinds of materials such as pure elements, metallic materials, glasses, geological materials (rocks and minerals), biological materials, polymers and many different kinds of organic and inorganic compounds. This paper reviews the findings of Bridgman and his successors from 1935 to 1988 using the HPT method and summarizes their historical importance in recent advancement of materials, properties, phase transformations and HPT machine designs.
390 citations
Saint Petersburg State University1, Ufa State Aviation Technical University2, National University of Sciences and Technology3, Monash University, Clayton campus4, Kyushu University5, University of Southampton6, University of Southern California7, University of Vienna8, North Carolina State University9, Nanjing University of Science and Technology10
TL;DR: The use of severe plastic deformation (SPD) has been extensively studied in the last decade as discussed by the authors, leading to the introduction of a range of nanostructural features, including nonequilibrium grain boundaries, deformation twins, dislocation substructures, vacancy agglomerates, and solute segregation and clustering.
Abstract: It is now well established that the processing of bulk solids through the application of severe plastic deformation (SPD) leads to exceptional grain refinement to the submicrometer or nanometer level. Extensive research over the last decade has demonstrated that SPD processing also produces unusual phase transformations and leads to the introduction of a range of nanostructural features, including nonequilibrium grain boundaries, deformation twins, dislocation substructures, vacancy agglomerates, and solute segregation and clustering. These many structural changes provide new opportunities for fine tuning the characteristics of SPD metals to attain major improvements in their physical, mechanical, chemical, and functional properties. This review provides a summary of some of these recent developments. Special emphasis is placed on the use of SPD processing in achieving increased electrical conductivity, superconductivity, and thermoelectricity, an improved hydrogen storage capability, materials for use in biomedical applications, and the fabrication of high-strength metal-matrix nanocomposites.
357 citations
TL;DR: In this article, the authors provide a critical overview of the properties of bulk nanoSPD materials, with a focus on the fundamentals for the observed extraordinary properties, including the unique nanostructures that lead to the superior properties, the underlying deformation mechanisms, critical issues that remain to be investigated, future research directions, and the application potential of such materials.
Abstract: Bulk nanoSPD materials are materials with nanostructural features, such as nanograins, nanoclusters, or nanotwins, produced by severe plastic deformation (SPD) techniques. Such nanostructured materials are fully dense and contamination free and in many cases they have superior mechanical and functional properties. Here, we provide a critical overview of such materials, with a focus on the fundamentals for the observed extraordinary properties. We discuss the unique nanostructures that lead to the superior properties, the underlying deformation mechanisms, the critical issues that remain to be investigated, future research directions, and the application potential of such materials.
256 citations
Cites background from "Twenty-five years of ultrafine-grai..."
...In addition to grain refinement down to the nanometer range, grain boundary structure engineering is also important because boundaries having different structures can exhibit specific transport mechanisms, in terms of deformation and diffusion, and this can be used to control the properties.[7,187] This opens up the potential for developing new ways for improving the properties of ultrafine-grained materials....
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...types of grain boundaries are formed by SPD processing and they may be classified as [2,7]...
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References
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01 Sep 1951
TL;DR: In this paper, an attempt is made to explain the observed phenomena in the yielding and ageing of mild steel, described in two previous papers, in the general terms of a grain-boundary theory.
Abstract: An attempt is made here to explain the observed phenomena in the yielding and ageing of mild steel, described in two previous papers, in the general terms of a grain-boundary theory. On this hypothesis, a satisfactory explanation of the variation of the lower yield point with grain size may be developed. It is shown that strain-ageing must involve two processes: a healing of the grain-boundary films, coupled with a hardening in the grains themselves. A discussion of the possible nature of the grain-boundary film is also undertaken.
5,893 citations
TL;DR: In this article, the authors present methods of severe plastic deformation and formation of nanostructures, including Torsion straining under high pressure, ECA pressing, and multiple forging.
5,763 citations
TL;DR: In this article, a review examines recent developments related to the use of ECAP for grain refinement including modifying conventional ECAP to increase the process efficiency and techniques for up-scaling the procedure and for the processing of hard-to-deform materials.
3,669 citations
TL;DR: High pressure torsion (HPT) is a well-known technique for metal forming as discussed by the authors, where samples are subjected to a compressive force and concurrent torsional straining.
2,499 citations
TL;DR: In this article, it is suggested that mosaic boundaries and boundaries between grains of nearly the same orientation may not serve as sources or sinks of the diffusion currents, in which case the creep rate will depend only on the configuration of grain boundaries having a sizable orientation differen...
Abstract: According to a suggestion of Nabarro, any crystal can change its shape by self‐diffusion in such way as to yield to an applied shearing stress, and this can cause the macroscopic behavior of a polycrystalline solid to be like that of a viscous fluid. It is possible that this phenomenon is the predominant cause of creep at very high temperatures and very low stresses, though not under more usual conditions. The theory underlying it is developed quantitatively, and calculations of rate of creep, or equivalently of effective viscosity, are given for aggregates of quasi‐spherical grains and for wires composed of cylindrical grains. Allowance is made for the effect of tangential stress relaxation at the grain boundaries. It is suggested that mosaic boundaries and boundaries between grains of nearly the same orientation may be unable to serve as sources or sinks of the diffusion currents, in which case the creep rate will depend only on the configuration of grain boundaries having a sizable orientation differen...
2,214 citations