Papers by Keyword: Severe Plastic Deformation (SPD)

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Authors: Radomír Kužel, Zdeněk Matěj, Miloš Janeček
Abstract: X-ray diffraction (XRD) studies of ECAP (equal-channel angular pressing) materials were performed after annealing and by in-situ measurements in XRD high-temperature chamber for samples prepared by different number of passes and number of revolutions, respectively. Main attention was given to Cu and Cu-Zr samples. Significant dependence on number of passes was found for ECAP samples. In-situ measurements were focused not only on temperature dependence but also on time evolution of the diffraction line profiles. Evaluation in terms of dislocation densities, correlation and crystallite size and its distribution was performed by our own software MSTRUCT developed for total powder diffraction pattern fitting. Abnormal growth of some grains with annealing is well-known for copper and leads to the creation of bimodal microstructure. Therefore a special care must be given to the evaluation and a model of two Cu components (larger and smaller crystallites) was fitted to the data if an indication of some crystallite growth appears either in the XRD line profile shape or in two-dimensional diffraction patterns.
279
Authors: Xavier Sauvage
Abstract: Concentration gradients resulting from long range diffusion during Severe Plastic Deformation (SPD) have been investigated with the 3D Atom Probe technique (3D-AP). First, in a pearlitic steel where alloying elements (Mn, Si and Cr) are partitioned between the ferrite and carbides in the non-deformed state. After processing by High Pressure Torsion (HPT), they are homogeneously distributed in the nanostructure, indicating that long range diffusion occurred along with the dissolution of carbides. 3D-AP data of a Cu-Fe composite processed by HPT show as well a significant interdiffusion of Cu and Fe, probably promoted by additional vacancies. On the basis of these experimental data, and using the theory described for irradiated materials, vacancy fluxes and vacancy production rates were estimated assuming that new vacancies are continuously produced and eliminated on grain boundaries.
433
Authors: J. Zhang
Abstract: Cyclic extrusion is a new bulk deformation method. It consists of two steps. In the first step a part of the work piece will be indirectly extruded. In the second step the extruded part will be backwards pressed into the bulk again so that the original shape of the work piece is retained. Similar to ECAP, cyclic extrusion can be repeated many times without shape change. On the other hand, cyclic extrusion can be applied locally on a work piece so that local grain refining or work hardening is possible. Magnesium alloy AZ31 was cyclically extruded at 400 °C with different tools. The grain size was refined from 800 +m to 15 +m. The local grain refining in the surface zone with cyclic extrusion improved the rollability of cast AZ31. Pure aluminium specimens were cyclically extruded up to 2.5 times, which corresponds to a deformation degree of -7. The microstructure changes were examined with EBSD.
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Authors: Nariman A. Enikeev, T.S. Orlova, Igor V. Alexandrov, A.E. Romanov
319
Authors: Qing Nan Shi, Yong Jin Chen, Jun Li Wang
Abstract: In the paper, the study was conducted on the characteristics of microstructures and orientations of UFG pure copper and 6061 aluminum alloy prepared by AARB, ECAP and CECC severe plastic deformation processes, in which SEM, TEM, EBSD and X-ray diffraction techniques were employed. The result of the study shows that microstructures, mainly composed of subgrains and dislocation kinks, are profuse in the UFG materials by the three SPDs. These kinds of microstructures have the strength of the materials much enhanced and the toughness heavily decreased. In these processes, shear deformation makes gains get finer and finer with the existence of the preferred orientations in the prepared UFG materials. Nevertheless, CECC shows the heaviest effect on the grain refining and the preferred orientation weakening.
343
Authors: G.Y. Deng, C. Lu, L.H. Su, J.T. Li, H.T. Zhu, X.H. Liu, K. Tieu
Abstract: In order to improve the efficiency of grain refinement, a study on the modified process (called Non-equal channel angular pressing) from the conventional equal channel angular pressing has been conducted. The deformation behavior of aluminum alloy AA1050 deformed by the Non-equal channel angular pressing which has a smaller width in the exit channel than the entry channel was examined based on the finite element simulations. The results revealed that a smaller ratio of dE and dI (dE/dI) leads to a larger equivalent plastic strain. It is not only beneficial to enhance the plastic deformation but also very helpful to get rid of the development of dead zone in the outer corner of die by decreasing the exit channel width by comparing with the conventional process.
442
Authors: Marcello Cabibbo, E. Evangelista, C. Scalabroni, Ennio Bonetti
Abstract: The microstructural evolution with strain was investigated either in a Zr-modified 6082 Al-Mg-Si alloy and in the same alloy added with 0.117wt.% Sc, subjected to severe plastic deformations. Materials were deformed by equal-channel angular pressing using route BC, up to a true strain of ∼12. A strain of ~4 produced a sub-micrometer scale microstructure with very fine cells (nanometer scale) in the grain interior. The role of fine dispersoids (Al3(Sc1-x,Zrx)) was investigated by transmission electron microscopy techniques and discussed. Dispersoids were responsible for a more complex dislocation substructure with strain. Compared to the commercial parent alloy, block wall formation and propagation were favored by the presence of Sc-Zr containing dispersoids, while cell boundary evolution was less affected, compared to the commercial parent alloy. Mean misorientation across block walls increased with strain much more in the Sc-Zr containing alloy, reaching a plateau, starting from a true strain of ∼8. Misorientation across cell boundaries continuously increased to ∼8° and ∼5° for the Sc-Zr and Zr containing alloy, respectively.
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Authors: Seung Chae Yoon, Do Minh Nghiep, Sun Ig Hong, Z. Horita, Hyoung Seop Kim
Abstract: Manufacturing bulk nanostructured materials with least grain growth from initial powders is challenging because of the bottle neck of bottom-up methods using the conventional powder metallurgy of compaction and sintering. In this study, bottom-up type powder metallurgy processing and top-down type SPD (Severe Plastic Deformation) approaches were combined in order to achieve both full density and grain refinement of metallic powders. ECAP (Equal-Channel Angular Pressing), one of the most promising processes in SPD, was used for the powder consolidation method. For understanding the ECAP process, investigating the powder density as well as internal stress, strain and strain rate distribution is crucial. We investigated the consolidation and plastic deformation of the metallic powders during ECAP using the finite element simulations. Almost independent behavior of powder densification in the entry channel and shear deformation in the main deformation zone was found by the finite element method in conjunction with a pressure dependent material yield model. Effects of processing parameters on densification and density distributions were investigated.
173
Authors: Reinhard Pippan, Stephan Scheriau, Anton Hohenwarter, Martin Hafok
Abstract: The improvements in the design of the HPT tools lead to a well defined torsion deformation and permits, therefore, a comparison with other SPD-techniques. The design of the tools, the advantages and disadvantages of HPT, as well as the limitation in the sample size are discussed.
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Authors: Soon Vern Yee, Zuhailawati Hussain, Abu Seman Anasyida, Muhammad Syukron, Indra Putra Almanar
Abstract: This study investigated the effect of severe plastic deformation (SPD) and artificial ageing treatment on mechanical properties of cast Al-Mg-Si alloy. 6061-T6 aluminum alloy was remelted and casted into a rod of 13mm in diameter and 60mm in length. The rod samples were then subjected to equal channel angular pressing (ECAP) for SPD process, up to 2 passes, through Bc route. Cast and ECAPed samples were solution heat treated at 530 °C, quenched in water and held at 180 °C at various ageing time to determine the effect of artificial ageing. Cast alloy consisted of α phase grains that were surrounded by Mg2Si particles locating at the grain boundaries. The hardness increased with accumulative applied strain by 2-pass ECAP process with the value of 99.4 Hv. For heat treated samples, maximum hardness was achieved after 5-hour ageing.
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