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排序方式: 共有502条查询结果,搜索用时 46 毫秒
81.
Konrad Güth Julia Lyubina Bernhard Gebel Ludwig Schultz Oliver Gutfleisch 《Journal of magnetism and magnetic materials》2012
This paper reports on the grain refinement in dynamic hydrogenation disproportionation desorption and recombination (d-HDDR) processed Nd-rich Nd2Fe14B and stoichiometric Nd2Fe14B powders using high pressure reactive milling (HPRM) followed by a subsequent desorption and recombination. In contrast to the dynamic-HDDR processed anisotropic powder with a grain size of the Nd2Fe14B phase of 300 nm, the new approach yields a further reduction of the Nd2Fe14B1 grain size to less than 70 nm. Nd-rich Nd2Fe14B powder produced by HPRM and subsequent desorption exhibits a coercivity μ0iHc=1.35 T and a remanence of 0.80 T. In the stoichiometric material, the reduction of the Nd-content leads to an increase in remanence to 0.85 T. Additionally, it is demonstrated that highly anisotropic powders can also be obtained by dynamic-HDDR processing of stoichiometric Nd2Fe14B powders. 相似文献
82.
A new double perovskite oxide holmium magnesium zirconate Ho2MgZrO6 (HMZ) was prepared by solid state reaction technique. The crystal structure has been determined by powder X-ray diffraction which shows monoclinic phase at room temperature with cell parameters a = 9.3028 ± 0.0030 Å, b = 5.2293 ± 0.0008 Å, c = 4.4009 ± 0.0009 Å, β = 103.3746 ± 0.0166°. An analysis of complex permittivity with frequency was carried out assuming a distribution of relaxation times. The frequency dependent electrical data are analyzed in the framework of conductivity and electric modulus formalisms. At the high temperature range, conductivity data satisfy the variable range hopping (VRH) model. In this regime, the conductivity of sample obeys Mott’s T1/4 law, characteristic of VRH. High temperature data indicates the formation of thermally activated small polarons. The scaling behaviour of imaginary part of electric modulus suggests that the relaxation describes the same mechanism at various temperatures. 相似文献
83.
Yubo ChenDengjie Chen Ran RanHee Jung Park Chan KwakSung Jin Ahn Kyeong Suk MoonZongping Shao 《Electrochemistry communications》2012,14(1):36-38
Nickel oxide was introduced as a grain growth inhibitor into Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF) electrode to increase its activity for oxygen reduction reaction. Small amount of NiO can effectively suppress the grain growth of BSCF by spinning the grain boundary and thus increase the electrode surface area, while the particle connection is not obviously affected. Electrochemical impedance spectra of symmetric cells indicate that the electrode activity for oxygen reduction is indeed effectively improved by introducing NiO additive. At 600 °C, area specific resistance of BSCF+5wt.% NiO is about 36.5% lower than that of pure BSCF electrode. Single cell tests also demonstrate an improved cell power output by introducing NiO additive. It implies that the adoption of a sintering inhibitor may be a facile and practical way to increase electrode activity for oxygen reduction. 相似文献
84.
Rémi Dingreville 《Journal of the mechanics and physics of solids》2008,56(5):1944-1954
In this paper, interfacial excess energy and interfacial excess stress for coherent interfaces in an elastic solid are reformulated within the framework of continuum mechanics. It is shown that the well-known Shuttleworth relationship between the interfacial excess energy and interfacial excess stress is valid only when the interface is free of transverse stresses. To account for the transverse stress, a new relationship is derived between the interfacial excess energy and interfacial excess stress. Dually, the concept of transverse interfacial excess strain is also introduced, and the complementary Shuttleworth equation is derived that relates the interfacial excess energy to the newly introduced transverse interfacial excess strain. This new formulation of interfacial excess stress and excess strain naturally leads to the definition of an in-plane interfacial stiffness tensor, a transverse interfacial compliance tensor and a coupling tensor that accounts for the Poisson's effect of the interface. These tensors fully describe the elastic behavior of a coherent interface upon deformation. 相似文献
85.
Abigail Hunter 《Journal of the mechanics and physics of solids》2008,56(11):3181-3190
Length scale parameters introduced in gradient theories of plasticity are calculated in closed form with a continuum dislocation based theory. The similarity of the governing equations in both models for the evolution of plastic deformation of a constrained thin film makes it possible to identify parameters of the gradient plasticity theory with the dislocation based model. A one-to-one identification is not possible given that gradient plasticity does not account for individual dislocations. However, by comparing the mean plastic deformation across the film thickness we find that the length scale parameter, l, introduced in the gradient plasticity theory depends on the geometry as well as material constants. 相似文献
86.
Crystal plasticity finite element analysis of cyclic deformation of compatible type FCC bicrystals are performed. The model specimen used in the analysis is a virtual FCC bicrystal with an isotropic elastic property; therefore, the effect of constraint due to elastic incompatibility does not appear. The results of the analysis show the strain-amplitude-dependence of both the organization of the GND structure and the stress–strain behavior. The calculated stress–strain curve with the largest strain amplitude shows additional cyclic hardening. The microscopic mechanisms of the strain-amplitude-dependent organization of the GND structure and additional cyclic hardening behavior are discussed in terms of the activation of secondary slip system(s). Finally, the effects of the elastic anisotropy, the lattice friction stress and the interaction between dislocations are also argued. 相似文献
87.
88.
Research trends in metal plasticity over the past 25 years are briefly reviewed. The myriad of length scales at which phenomena involving microstructure rearrangement during plastic flow is discussed, along with key challenges. Contributions of the author’s group over the past 30 years are summarized in this context, focusing on the statistical nature of microstructure evolution and emergent multiscale behavior associated with metal plasticity, current trends and models for length scale effects, multiscale kinematics, the role of grain boundaries, and the distinction of the roles of concurrent and hierarchical multiscale modeling in the context of materials design. 相似文献
89.
Calvin J. Gardner Brent L. AdamsJohn Basinger David T. Fullwood 《International Journal of Plasticity》2010
Recent advances in high-resolution electron backscatter diffraction (EBSD)-based microscopy are applied to the characterization of elastic fields and incompatibility structures near the grain boundaries (GBs) in polycrystals. Two main recoveries are reported here: surface geometrically necessary dislocation (density) tensors, as described by Kröner, and the elastic fields near cracks (unconsolidated portions of interface) in loaded samples. Context for the application of these recoveries is described, using Green’s function solutions for combined heterogeneity and dislocation. Featured recoveries required the cross-correlation based determination of the elastic distortion tensor, aided by application of the simulated pattern method, and determination of the absolute pattern center utilizing the expected pattern properties in a spherical Kikuchi reference frame. High-resolution data obtained along an ultrasonically consolidated nickel boundary of varying amalgamation indicates that the imposed traction free boundary condition at free surfaces is well observed in the data structure. Further, high-resolution data acquired near a single grain boundary in well-annealed, low content steel suggests that it may be possible to measure the intrinsic elastic properties of GBs. 相似文献
90.
同时测定粮谷中痕量锰铁铜锌的人工神经网络辅助分光光度法 总被引:4,自引:0,他引:4
在pH 9.5时,Mn(Ⅱ )、 Fe(Ⅲ )、 Cu(Ⅱ )和 Zn(Ⅱ )均与 2-(5-溴-2-吡啶偶氮 )-5-二乙氨基苯酚和非离子表面活性剂聚乙二醇辛基苯基醚发生高灵敏的显色反应,生成稳定的三元胶束络合物 ,其λ max分别为 566、 560、 562和 559 nm,表明吸收光谱严重重叠 ; 在相应λ max处,其表观摩尔吸光系数分别为 1.13× 105、 7.32× 104、 1.02× 105和 1.04× 105 L· mol- 1· cm- 1。用模拟退火-误差反向传播人工神经网络辅助分光光度法,不经分离,同时测定了模拟样和粮谷样中的痕量锰、铁、铜和锌。详细研究了该算法的最佳计算条件。虽然体系的加和性较差,但由于该算法的优良性能,仍然取得了满意结果。 相似文献