共查询到20条相似文献,搜索用时 15 毫秒
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A new synthetic approach for fabrication of perforated hollow silica morphologies using colloidal template assemblies is demonstrated. As proof-of-principle, the polystyrene/silver colloidal assemblies had chemically modified surfaces. The template dissolution resulted in the fabrication of the submicron perforated hollow silica shells. The morphologies are characterized by transmission electron microscopy, energy dispersive spectroscopy and plasmon light extinction spectrophotometry. 相似文献
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Tailoring dislocation structures and mechanical properties of nanostructured metals produced by plastic deformation 总被引:1,自引:0,他引:1
The presence of a dislocation structure associated with low-angle dislocation boundaries and interior dislocations is a common and characteristic feature in nanostructured metals produced by plastic deformation, and plays an important role in determining both the strength and ductility of the nanostructured metals. The dislocation structure can be modified by post-process annealing and deformation which points to new ways of optimizing the mechanical properties. Such ways are demonstrated and discussed. 相似文献
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Joining by plastic deformation 总被引:2,自引:0,他引:2
Ken-ichiro Mori Niels Bay Livan Fratini Fabrizio Micari A. Erman Tekkaya 《CIRP Annals》2013,62(2):673-694
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In this research the effects of cold deformation and heating to the semi-solid temperature on microstructure and mechanical properties of cast dendritic and non-dendritic structures of A356 alloy were investigated. To produce the non-dendritic samples, the semi-solid slurry was obtained by electromagnetic stirring and rheoforged and then the samples were heated to semi-solid temperature. In order to impose the deformation to the dendritic and non-dendritic samples, multidirectional forging process was used. Non-dendritic samples were deformed with applying one to three passes of the multidirectional forging and then were kept at the semi-solid range of temperature again. Microstructural and mechanical properties of the deformed samples after and before heating were investigated. The dendritic structure after one pass of the multidirectional forging was kept at the semi-solid temperature to reach a different non-dendritic structure by strain induced melt activation process. Micro and macro hardness tests were used to study the mechanical properties of these samples. For metallographic examinations, scanning electron microscopy and the optical microscope equipped with the Clemex image analyzer software were used. The circular diameter of the heated rheoforged samples to semi-solid temperature that deformed to one pass of the multidirectional forging and then kept at semi-solid state was smaller than that of ones deformed to two and three passes and kept at semi-solid state. From the results achieved for the strain induced melt activation sample, it was obvious that this is an effective process to produce non-dendritic structure with approximately the same sphericity and lower globule size compared with other studied samples. 相似文献
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In recent years, materials with ultrafine grain size(UFG) have attracted much attention. By using severe plastic deformation(SPD) techniques, materials with fine grain size as small as 200 - 250 nm have been obtained.However, the nature of the grain boundaries has not been theoretically understood. It is still an unsolved question whether or not finer grain sizes down to 100 nm could he reached. A semi-quantitative model for the evolution of dislocation cells in plastic deformation was proposed. The linear stability analysis of this model leads to some interesting results, which facilitate the understanding of the formation of cell structures and of the factors determining the lower limit of the cell size of SPD materials. 相似文献
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研究淬火态和时效态U-Nb合金在机械加工和静拉伸时的可逆塑性变形,采用透射电子显微镜进行原位拉伸观察,结合变形前后及二次时效后合金的X射线衍射分析探讨U-Nb合金的塑性变形机制,利用时效方法探索消除加工变形的可行性。结果表明:高密度孪晶的相互吞并、长大及发生择优取向是该合金在变形初期的主要变形机制;淬火态和经150℃时效U-Nb合金的变形量差别不大,而经200℃时效U-Nb合金的加工变形量与前两者相比相对较小;利用200℃二次时效的方法消除塑性变形时,U-Nb合金的变形回复量可达50%以上。 相似文献
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N.V. Kazantseva N.V. MushnikovA.G. Popov P.B. Terent’evV.P. Pilyugin 《Journal of Alloys and Compounds》2011,509(38):9307-9311
Severe plastic deformation (mechanical activation in a hydrogen atmosphere and shear under pressure) effects on the hydrogenation of two titanium aluminides Ti3Al and TiAl-type alloy (B2) have been studied. It is shown that a conventional hydrogenation of the bulk samples allows forming the hydrides with high hydrogen content and high desorption temperature: TiAl (773 K, 1.76 mass%) and Ti3Al (1043 K, 2.94 mass%). In comparison with the conventional hydrogenation, the mechanical activation in a hydrogen atmosphere at room temperature allows one to obtain the hydrides of the TiAl (B2) and Ti3Al alloys with the reduced desorption temperature: TiAl (453 K, 1.96 mass%) and Ti3Al (531 K, 2.6 mass%). The shear under pressure has been applied to the sample before hydrogenation also leads to a reduction of the desorption temperature; however, it produces the phase transformation in the Ti3Al intermetallic compounds, which lowers the observed a maximum hydrogen content. 相似文献
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L. M. Rybakova 《Metal Science and Heat Treatment》1980,22(8):557-563
Conclusions Plastic deformation in tension (compression) occurs in stages associated with the development and accumulation of microdamage — destruction of the material. The mechanics of the deformation process, each stage of which depends on the characteristics of the deformation mechanism, can be judged from the S vs 1/2 diagram. On diagrams of true stress vs residual deformation there is a critical point — the point of inflection — which determines the beginning of destruction during plastic deformation and makes it possible to characterize the condition of the body in the process of deformation by the coefficients of destruction and quality, indicating the extent of the development of microdamage. The laws governing the development and accumulation of damage in plastically deformed material make it possible to characterize the behavior of the material in the region where neither the mechanical macromodels (mainly for the continuous solid state) nor micromodels of the physics of metals and alloys based on data concerning lattice defects can be used. Concepts of the plastic-destructional deformation and methods for quantitative determination of the degree of destruction make it possible to solve problems of material sciences associated with the quality of a material, its reliability, and service life. Concepts of the development of destruction in plastically deformed material are useful in studying the laws governing the accumulation of damage under different deformation conditions, particularly with surface treatments. They are of particular importance in order to explain the role of surface layers of metal in the overall macroscopic process, since they may determine the behavior of the material as a whole.Institute of Machine Sciences. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 8, pp. 17–22, August, 1980. 相似文献
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Conclusions The observed difference in the rate of strain hardening of sintered and case iron may be due to rotation of the particles in the process of cold plastic deformation of the P/M material, leading to substantial stress relaxation. The characteristics of the mechanism of plastic deformation in sintered materials must be kept in mind in developing techniques of cold bulk pressing, particularly to reduce deformation stresses.PO ZIL. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 2–5, October, 1982. 相似文献
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A newly invented method, called the rotation shear method, to achieve the high strain by the rotation shear is introduced in this paper. Equations for the calculation of the strain and the strain rate are presented. An experiment was performed with pure aluminum and the results showed that a shear strain up to 8.37 was achieved and the transmission electron microscope observation confirmed that an ultra-fine grained material with the size below 700 nm was obtained. 相似文献
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T. Ungár I. Alexandrov M. Zehetbauer 《JOM Journal of the Minerals, Metals and Materials Society》2000,52(4):34-36
The microstructures of ultrafine-grained nanostructured materials developed by severe plastic deformation are widely varied in their grain size and grain-size distribution; grain boundaries and their structures; lattice defects, especially dislocations; point defects; and impurities. All of these features can be influenced by the way severe plastic deformation is applied, and thereby have decisive effects on the physical and mechanical properties of the material. Probably, the most important factors determining microstructure are the imposed stress tensor, the degree and rate of strain, the temperature of deformation, the chemical composition of the deformed material, and the type of crystal lattice, showing that in order to develop specific properties, it is crucial to understand and optimize the microstructure. 相似文献