Papers by Keyword: Ultra-Fine Grain (UFG)

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Authors: Aicha Loucif, Thierry Baudin, François Brisset, Roberto B. Figueiredo, Rafik Chemam, Terence G. Langdon
Abstract: This investigation uses electron backscatter diffraction (EBSD) to study the development of microtexture with increasing deformation in an AlMgSi alloy having an initial grain size of about 150 µm subjected to high pressure torsion (HPT) up to a total of 5 turns. An homogeneous microstructure was achieved throughout the disc sample at high strains with the formation of ultra-fine grains. Observations based on orientation distribution function (ODF) calculation reveals the presence of the torsion texture components often reported in the literature for f.c.c. materials. In particular, the C {001}<110> component was found to be dominant. Furthermore, no significant change in the texture sharpness was observed by increasing the strain.
Authors: Ji Xiang Gao, Xin Ping Mao, L.J. Li
Abstract: Based on the characteristics of raw materials in EAF-TSCR, the composition of VN micro-alloyed was designed, the processes of the steelmaking, continuous casting, soaking, rolling, cooling were controlled, and at last the VN Micro-alloying high strength steel with ultra-fine grain was developed. The ferrite grain size of the steel reaches 3.0 to 4.0 microns, and the yield strength of which reaches 550MPa. Besides, the steel processes good toughness, cold formability and weldability. In the end, the strengthening mechanism of the ultra-fine steel was discussed.
Authors: Bing Zhang, Zhong Wei Chen, Shou Qian Yuan, Tian Li Zhao
Abstract: In this paper, accumulative roll bonding (ARB) has been used to prepare the Al/Mg alloy multilayer structure composite materials with 1060Al sheet and MB2 sheet. The evolution of microstructure of the cladding materials during ARB processes was observed by optical microscope, scanning electron microscopy, and micro-hardness was measured by micro-hardness tester. The results show that a multilayer structure material of Al/Mg alloy with excellent bonding characteristics and fine grained microstructure was prepared by ARB processes. With the ARB cycles increasing, Mg alloy layer in multilayer composite material was necked and fractured, and the hardness of the Al and Mg alloy was increased. Average grain size was less than 1μm after ARB4 cycles.
Authors: Rampada Manna, N.K. Mukhopadhyay, G.V.S. Sastry
Abstract: Grain refinement of aluminum deformed by equal channel angular pressing is strongly dependent on the amount of strain. The refinement process at low to high strain level involves elongation of the existing grains by shear deformation, their subdivision into bands and subgrain formation within bands, intersection of the bands during subsequent passes and finally conversion of the subgrains to grains by continuous dynamic recrystallization process. At room temperature the conversion of subgrains to grains takes place by progressive lattice rotation.
Authors: Hiromi Miura, M. Ito
Abstract: A commercial AZ61 magnesium (Mg) alloy composed of coarse initial grains was multi-directionally forged (MDFed) under decreasing temperature conditions from 673 K to 463 K up to a cumulative strain of ΣΔε = 6.4 at a true strain rate of 3 × 10-3 s-1. A pass strain of Δε = 0.8 was employed. The average grain size decreased gradually with an increase in the cumulative strain. After straining to ΣΔε = 6.4 (i.e., after 8 passes of MDF), equiaxed ultrafine grains (UFGs) with an average size of approximately 0.8 μm were uniformly produced. These grains were relatively coarse as compared with MDFed Mg alloys having initially finer grains. The hardness of the AZ61 Mg alloy increased monotonically up to 910 MPa with decreasing grain size. The Hall-Petch relationship held within this experimental condition.
Authors: Seong Hee Lee, Daejin Yoon, Hiroshi Utsunomiya
Abstract: Microstructural evolution of a copper alloy processed by accumulative roll-bonding (ARB) was investigated by EBSD analysis. The grains became thinner and elongated to the rolling direction with increasing the number of ARB cycles. The subdivision of the grains to the rolling direction actively begins to occur after 5 cycles of the ARB, resulting in formation of ultrafine grains with small aspect ratio. After 8 cycles, the ultrafine grained structure with the average grain diameter of 250nm developed in almost whole regions of the sample. In addition, the fraction of high-angle grain boundaries increased with the number of ARB cycles and reached about 0.7 after 8 cycles. The texture development of the ARB processed samples was different depending on the number of ARB cycles and the positions in the thickness.
Authors: Kun Xia Wei, Wei Wei, Igor V. Alexandrov, Qing Bo Du, Jing Hu
Abstract: Microstructure, mechanical properties and electrical conductivity in Cu-0.73%Cr alloy after HPT process and the subsequent aging treatment have been investigated. Ultrafine grained structure with the grain size ~150 nm has been achieved after the HPT and the subsequent aging treatment. Ultrafine grains with some growth twins were preserved in the overaged state, showing high thermal stability. The peak microhardness and tensile strength of Cu-0.73%Cr alloy after the HPT was found at 480 °C for 2 hours. Electrical conductivity shows an increase trend in the different aging states.
Authors: Garima Sharma, Apu Sarkar, Indradev Samajdar, J.K. Chakravartty
Abstract: The present study reports the microstructure evolution and mechanical behaviour of severe plastically deformed pure Cu under cryogenic conditions. The samples were severely deformed by cryo rolling upto 50%, 75% and 95% deformation. Microstructure evolution of cryo rolled samples has been characterized by using optical, TEM and EBSD technique. The rolled samples were heat treated at various temperatures so as to control the recrystallization in the severely deformed samples. The effect of recrystallization on the mechanical behaviour was investigated in detail by tensile testing. The EBSD analysis performed on 95% rolled + heat treated samples showed that partial recystallized microstructure demonstrate an optimum combination of strength and ductility in cryo rolled Cu.
Authors: Erell Bonnot, François Brisset, Anne Laure Helbert, Thierry Baudin
Abstract: The Armco iron is one of the purest commercial iron with very low levels of carbon, oxygen and nitrogen. In order to improve the mechanical properties, it is worth applying severe plastic deformation to obtain ultrafine-grained bulk materials, with grain size lower than 1 μm. In this study, samples of Armco iron were subjected to a technique of severe plastic deformation named Accumulative Roll Bonding (ARB). This method consists in rolling to 50% two sheets pack of which the stacked surfaces were initially cleaned. Then, the rolled strip is sectioned in two halves, cleaned and stacked again and the procedure of roll-bonding repeated. Practically, the process can be repeated without limits. The important parameter of ARB is the number of cycles and then the consequent number of layers of the final sample. By means of the Electron Backscattered Diffraction (EBSD) technique, the evolution of both microstructure and texture as regard to the number of ARB cycles was studied. The analysis of mean grains size and high angle grain boundaries (HAGB) fraction as a function of the number of cycles showed an early formation of a subgrained structure with low angle boundaries and then the evolution of the microstructure towards an ultrafine-grained structure with an increase of HAGB.
Authors: Cheng Jun Liu, Hong Liang Liu, Mao Fa Jiang
Abstract: The effects of the rare earth (RE) element on the microstructure of a hot-rolled low carbon steel (B450NbRE) were investigated under different heat treatment conditions. It was found that the B450NbRE steel with ultrafine grained structure could be successfully prepared with a certain content of RE additive under an appropriate heat treatment temperature between A1 (717°C) and A3 (880°C). The corresponding critical temperature increases with decreasing the RE content. For instance, the critical temperature is 800°C for the RE content of 0.0140 wt.%, but it increases to 850°C as the RE content decreases to 0.0075 wt.%
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