1,721,025 research outputs found
Developments in the use of ECAP processing for grain refinement
No full textEqual-channel angular pressing (ECAP) is one of the most efficient techniques of severe plastic deformation for the production of bulk ultrafine-grained metals. During the last decade the intensive developments of ECAP have been associated with numerous modifications of the die-set design as well as establishing new processing routes and regimes. This paper describes the various types of ECAP that have been developed recently and applied for grain refinement. Special attention is focused both on new trends in ECAP processing associated with the development of continuous processing and on its efficiency
Report of International NanoSPD Steering Committee and statistics on recent NanoSPD activities
No full textThe Université de Lorraine in Metz, France, is the selected site for the 6th International Conference on Nanomaterials by Severe Plastic Deformation (NanoSPD6) following a series of five earlier conferences. This introductory paper reports on several major developments in NanoSPD activities as well as on very recent NanoSPD citation data which confirm the continued growth and expansion of this important research area. Close attention is given to the topics of workshops, conferences and seminars organized during these last three years as well as on books and reviews published prior to the NanoSPD6 conference. A special concern of the committee is in introducing and discussing the appropriate terminology to be applied in this new field of materials science and engineerin
Towards superstrength of nanostructured metals and alloys processed by SPD
No full textThe metals and alloys subjected to severe plastic deformation can possess not only ultrafine-grained (UFG) structure but also specific nanostructural features, such as non-equilibrium grain boundaries, nanotwins, grain boundary segregations and nano particles. The Authors consider in the present work the role of these features in exhibition of high strength of nanostructured metals and alloys. In particular, it is demonstrated that the presence of grain boundary segregations and non-equilibrium boundaries can result in yield stress values that considerably exceed those predicted from the Hall-Petch relation for the given material
Microhardness and microstructural evolution in pure nickel during high-pressure torsion
No full textThe microhardness and microstructural evolution during high pressure torsion testing in samples of pure nickel were investigated. Results were obtained on Ni samples subjected to annealing prior to high pressure torsion. A detailed TEM and X ray study were used. During torsion, the final microstructure was independent of the grain size. It was demonstrated that the processing parameters of strain and applied pressure were important for microhardness refinement and increased microhardness during high pressure torsion.<br/
Microstructure decomposition and unique mechanical properties in an ultrafine-grained Al-Zn alloy processed by high-pressure torsion
No full textAn ultrafine-grained (UFG) Al-30wt.%Zn alloy was processed by high-pressure torsion (HPT) and then the mechanical and microstructural properties were investigated using depth-sensing indentations (DSI), focused ion beam (FIB), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Emphasis was placed on the microstructure changes due to HPT processing as well as the effects of grain boundaries and the unusually high strain rate sensitivity. The deformation characteristics are explained by the formation of a Zn-rich phase which wets the Al/Al grain boundaries and enhances the role of grain boundary sliding in this UFG alloy. The occurrence of intensive grain boundary sliding in this UFG alloy at room temperature was also demonstrated by deforming micro-pillars. It is shown that, as a result of grain boundary sliding, the plastic deformation process of the UFG samples remains stable even at the micro-scale without the intermittent flow and detrimental strain avalanches which are an inherent feature of micro-size conventional crystals. This result illustrates the advantage of using UFG materials for effective applications in micro-devices. <br/
An overview: fatigue behaviour of ultrafine-grained metals and alloys (in issue on fatigue lifetime prediction of metals based on microstructural behaviour)
No full textThe objectives of the present study were to assess and to optimize the fatigue behaviour in strain-controlled tests of different ultrafine-grained (UFG) metals and alloys (Cu, Al, AA6061, ?-brass) prepared by equal channel angular pressing (ECAP). Quite generally, the UFG materials investigated exhibited shorter fatigue lives in the low-cycle fatigue (LCF) regime than corresponding conventional grain (CG) size specimens. In all cases, the fatigue lives could be enhanced appreciably by a suitable heat treatment following ECAP without, however, paralleling the fatigue lives of the CG specimens. The microstructural reasons for this behaviour are discussed, and a microstructure-based fatigue life model for UFG materials is presented
Characteristics of superplasticity in an ultrafine-grained Aluminum Alloy processed by ECA pressing
No full textEqual-channel angular pressing was used to process a commercial 1421 aluminum alloy at temperatures from 340 to 410 °C. An optimum ultrafine microstructure was achieved after pressing at 370 °C with an equiaxed grain size of ~0.3–0.4 ?m. Tensile testing showed this material is superplastic at 400 °C with elongations up to ~1500%. Offsets in surface marker lines demonstrate grain boundary sliding is the dominant flow process
Fundamentals of superior properties in bulk nanospd materials
No full textBulk 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
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