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971.
S. L. Yuan Z. J. Yang K. Kadowaki J. Q. Li T. Kimura H. Takeya 《Philosophical Magazine Letters》2013,93(2):169-177
Abstract Vortex dynamics in La1.86Sr0.14CuO4 have been studied by the measurement of ρc //i (T, H), where ρc //i is the c-axis resistivity for H//i (i = c or a-b). We argue that, at temperatures higher than the irreversibility temperature T irr, the usual vortex picture breaks down owing to the thermal motion of vortices, resulting in a T- and T in-dependent anisotropic parameter γ. After taking into account the dependence of γ on T and T irr, we show that at each given temperature we can rescale the ρc //a-b (T, H) data onto the corresponding ρc //c (T, H) curves. This scaling property clearly indicates that the Lorentz-force-free mechanism is responsible for ρc //a-b (T, H). Furthermore, we also show that the measured ρc //a-b (T, H) data can be explained in terms of the recently developed extended Josephson coupling model which is verified by rescaling ρc //a-b (T) data for various fields onto a single curve. 相似文献
972.
Bing Q. Han Enrique J. Lavernia Farghalli A. Mohamed 《Philosophical Magazine Letters》2013,93(2):89-96
The mechanical behaviour of bulk ultrafine-grained Al-7.5 wt% Mg alloy consolidated from cryomilled powders has been investigated. The experimental data show that the alloy exhibits high strength, low strain hardening, serrated flow and relatively high ductility. In addition, the data indicate that the yield strength in tension is essentially equal to that in compression. The yield and flow strengths of the alloy are discussed in terms of strengthening processes that are related to grain size, the Orowan mechanism and solid-solution hardening. The serrations in the stress-strain curve are discussed in terms of dynamic strain ageing and deformation twinning. 相似文献
973.
Abstract To study the grain boundaries of the technologically important RE13.75Fe80.25B6 (RE = Pr or Nd) permanent magnets, we developed a new method using small-angle dark-field imaging based on inner-potential differences at the grain boundaries, combined with high-resolution electron microscopy and nanoscale chemical analysis. In both the Pr- and Nd-based melt-quenched die-upset magnets we consistently observed a very thin Fe-rich amorphized intergranular phase at the boundaries, and this finding may have an impact on our understanding of the coercivity mechanism of these materials. Although the value of the method was demonstrated for transition metal-rare earth intermetallics, it may also be applied to grain-boundary studies in other materials. 相似文献
974.
Localised shear deformation of a material is usually identified as a particular feature of deformation inhomogeneity. Here, we show two different types of shear deformation-behaviour that occurred in Au–Cu multilayers subjected to microindentation load, namely, a cooperative-layer-buckling-induced shear banding in a nanoscale multilayer and a direct localised shearing across a layer interface along a shear plane in a submicron-scale multilayer. Theoretical analysis indicates that the formation of the two different types of shear deformation in the multilayers depends on a competition between the dislocation-pile-up-induced stress concentration at the layer interface and the barrier strength of the layer interface for glissile dislocation transmission. 相似文献
975.
D.V. Louzguine-Luzgin G.Q. Xie S. Li A. Inoue N. Yoshikawa M. Sato 《Philosophical Magazine Letters》2013,93(2):86-94
Metallic glasses exhibit low viscosity in a temperature range between the glass transition and the crystallization temperature, a feature that allows successful sintering of glassy powders. Microwave heating, being volumetric, has significant advantages over conventional heating in materials processing, such as substantial energy savings, high heating rates and process cleanliness. In the present study, we investigate the stability of Cu50Zr45Al5 glassy powders and the formation of a bulk two-component metallic glassy-crystal sample by microwave heating in a single-mode cavity (915 MHz) in an alternating magnetic field. 相似文献
976.
The structural evolution during crystal nucleation in supercooled Lennard–Jones liquids at a supercooling of 0.3T m (T m is the melting temperature) has been studied by molecular dynamic simulations. The icosahedral clusters are observed to compete with crystalline clusters in space, and rearrange before crystal nucleation. Both the stable face-centered-cubic and hexagonal-close-packed (hcp) structures and metastable body-centered-cubic (bcc) structures nucleate simultaneously, resulting in the formation of an incomplete bcc meso-layer in the nuclei. The nuclei form twinned crystal with five-fold axes through a successive twinning process bounded by planes with hcp atoms. 相似文献
977.
Using high-resolution electron microscopy, we investigated the initial stages of high-pressure-torsion-induced crystalline-to-amorphous transformation of TiNi. It is found that the deformation-induced amorphization initiated from dislocation core regions in the interior of grains and from grain boundaries. It is believed that both the energy stored in the dislocations and the energy stored in the grain boundaries contribute significantly to driving the crystalline-to-amorphous transformation. 相似文献
978.
Nanometre-sized kinks and cracks formed in 6H SiC under ball milling (BM) at room temperature have been observed and characterized on the atomic scale using high-resolution electron microscopy (HREM). Observations of the kinks show that numerous positive and negative partials are aligned at either of the kink boundaries, and the stacking sequences in the kink band are considerably different from those in the other areas. It was also observed that the (0001) lattice planes in the kink band are kinked, indicating that microplasticity occurs in the normally brittle material SiC under BM even at room temperature. HREM observations of cracks show that cracks previously observed by transmision electron microscopy are not completely open but are at the initiation stage of fracture. Inside a crack, one residual kink region can be clearly observed, which indicates a correlation between kink and crack, that is a crack evolves from a kink. 相似文献
979.
Helium generated in materials by the nuclear reaction (n,?α) is generally considered to be harmful. It is well-known that helium prompts not only the nucleation of interstitial-type dislocation loops, but also the nucleation of voids in metals and alloys irradiated with high-energy particles, which degrades their mechanical properties. In this study, however, we find that helium trapped by dislocations in Ni increases both the ultimate tensile strength and total elongation. 相似文献
980.
An k -phase Mn-Al-C single crystal was grown and annealed to obtain an intermediate stage of the k M transformation. The crystal was analysed by transmission electron microscopy, and direct evidence for the operation of the shear mode was obtained. The transformation occurs in two steps from the hcp structure ( k ) over the orthorhombic structure ( k ' phase) to the tetragonal phase. The study reveals the morphologies of k ' and , the necessity for reordering during the second transformation step ( k ' M ) which is not a purely martensitic transformation, and the selection of variants which is controlled by stresses through the selection of one k ' variant. 相似文献