Fabrication of perforated sub-micron silica shells

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.     

Tailoring dislocation structures and mechanical properties of nanostructured metals produced by plastic deformation

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.     

Effects of cold severe plastic deformation and heating on dendritic and non-dendritic structures: A356 alloy

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.     

剧烈塑性变形制备微纳米材料的变形细化机理

对剧烈塑性变形法(SPD)制备微纳米材料变形细化机理进行了总结归纳,着重介绍了位错变形和热机械变形两种机制,详细论述了材料在剧烈塑性变形加工过程中的组织转变特点,同时给出了SPD变形细化机制等研究方向的个人见解。     

累积叠轧焊强加工制备亚微米金属材料的研究

采用ARB(累积叠轧焊)的方法在多功能强力热轧机上对普碳钢Q235,L2纯铝分别进行了强加工试验,并利用电子万能材料试验机,SEM,TEM,EBSD等手段对材料力学性能、微观组织、缺陷进行了分析。结果表明,普碳钢材料的平均抗拉强度由385MPa提高到797.5MPa,平均晶粒尺寸减小到0.7μm;L2纯铝材料的抗拉强度由75.2MPa提高到190.44MPa,平均晶粒尺寸达到0.5μm;强加工引起的位错塞积对材料起到了强化作用。     

Evolution of dislocation cells during plastic deformation

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.     

U-Nb合金的可逆塑性变形及其消除方法

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。     

Severe plastic deformation and hydrogenation of the titanium aluminides

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.     

Destruction of metal during bulk and surface plastic deformation

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.     

Mechanism of cold plastic deformation of sintered iron

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.     

Severe plastic deformation introduced by rotation shear

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.     

Ultrafine-grained microstructures evolving during severe plastic deformation

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.