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排序方式: 共有190条查询结果,搜索用时 31 毫秒
31.
The paper focuses on the microstructural characterisation of secondary phases in an AZ91 magnesium alloy. The orientation
relationship and atomic structure of semi-coherent Mg/Mg17Al12 interfaces are studied by means of selected area diffraction, EDS and high resolution TEM. Besides the common Mg17Al12 semi-coherent platelets of high density and coarser incoherent Mg17Al12 particles, other, less frequent precipitates were found, rich in Al and Mn. The quasicrystalline nature of these precipitates
was detected by means of electron diffraction. 相似文献
32.
33.
The structure of an Al–Rh–Cu decagonal quasicrystal formed with two quasiperiodic planes along the periodic axis in an Al63Rh18.5Cu18.5 alloy has been studied by spherical aberration (Cs)-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM). Heavy atoms of Rh and mixed sites (MSs) of Al and Cu atoms projected along the periodic axis can be clearly represented as separate bright dots in observed HAADF-STEM images, and consequently arrangements of Rh atoms and MSs on the two quasiperiodic planes can be directly determined from those of bright dots in the observed HAADF-STEM image. The Rh atoms are arranged in pentagonal tiling formed with pentagonal and star-shaped pentagonal tiles with an edge-length of 0.76 nm, and also MSs with a pentagonal arrangement are located in the pentagonal tiles with definite orientations. The star-shaped pentagonal tiles in the pentagonal tiling are arranged in τ2(τ: golden ratio)-inflated pentagonal tiling with a bond-length of 2 nm. From arrangements of Rh atoms placed in pentagonal tilings with a bond-length of 2 nm, which are generated by the projection of a five-dimensional hyper-cubic lattice, occupation domains in the perpendicular space are derived. Al atoms as well as Rh atoms and MSs are represented as dark dots in an observed ABF-STEM image, and arrangements of Al atoms in well-symmetric regions are discussed. 相似文献
34.
An Al3Mn-type Al3(Mn, Pd) crystal and an Al–Mn–Pd decagonal quasicrystal (DQC) in an Al70Mn20Pd10 alloy are studied using a spherical aberration (Cs)-corrected scanning transmission electron microscope (STEM) with high-angle annular dark-field (HAADF) and annular bright-field (ABF) techniques, together with atomic-resolution energy dispersive X-ray spectroscopy (EDS). Mn and Pd atomic positions in the Al3(Mn, Pd) structure projected along the b-axis (pseudo-tenfold rotational axis) are represented by separate bright dots in observed HAADF-STEM images. Besides, Al as well as Mn and Pd atomic positions are represented as dark dots in ABF-STEM images. Most Mn and Pd atomic positions in the Al3(Mn, Pd) structure can be observed on atomic-resolution EDS maps. On the basis of the good correlation between the STEM images and the EDS maps, and also considering the structure of the Al3(Mn, Pd) crystal, which was determined by X-ray diffraction using a single crystal, observed HAADF and ABF-STEM images of the Al–Mn–Pd DQC have been interpreted. Pd and Mn atomic positions in the Al–Mn–Pd DQC can be detected on the observed EDS maps. It can be seen that Pd is enriched around the centre of the columnar clusters, having a decagonal section with 2 nm in diameter. It can therefore be concluded that Pd plays an important role in the stabilization of the decagonal clusters, which form the Al–Mn–Pd DQC structure. 相似文献
35.
36.
采用X射线衍射、透射电镜等手段研究了高压下Al65Cu20Fe15等快速凝固粉末中准晶及晶体相的相变问题,在800℃,6GPa条件下,准晶粉末中的晶体相基本上转变为二十面体准晶相。在常压下,准晶相在高温转变为晶体相.压力对相变热力学有显著影响。 相似文献
37.
本文用透射电子显微镜研究了快速冷凝Al_(47)Cu_(25)Fe_8Mg_(20)合金粉末。在淬火态粉末中,发现并确定了四个晶体相,在800℃热处理的粉末中,观察到了F型二十面体准晶相。 相似文献
38.
É. A. Arinshtein 《Theoretical and Mathematical Physics》2007,151(1):571-585
We compare properties of the crystal structure and of the quasicrystal model of liquid. We show that if the Lennard-Jones
potential is used to model the properties of argon, then the temperature of the phase transition between the densely packed
face-centered and the body-centered cubic structure is very close to the liquid-crystal transition temperature. Based on this,
we propose a model of the phase transition consisting in a change of just the short-range order, which then leads to a change
of the long-range order.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 151, No. 1, pp. 155–171, April, 2007. 相似文献
39.
M. J. Ablowitz B. Ilan E. Schonbrun R. Piestun 《Theoretical and Mathematical Physics》2007,151(3):723-734
We compute and study localized nonlinear modes (solitons) in the semi-infinite gap of the focusing two-dimensional nonlinear Schrödinger (NLS) equation with various irregular lattice-type potentials. The potentials are characterized by large variations from periodicity, such as vacancy defects, edge dislocations, and a quasicrystal structure. We use a spectral fixed-point computational scheme to obtain the solitons. The eigenvalue dependence of the soliton power indicates parameter regions of self-focusing instability; we compare these results with direct numerical simulations of the NLS equation. We show that in the general case, solitons on local lattice maximums collapse. Furthermore, we show that the Nth-order quasicrystal solitons approach Bessel solitons in the large-N limit. 相似文献
40.
According go the group representation theory, we derive the character formulae of representation-matrices of the期physical property gensors for the one-dimensional (1D) quasicrysgals. Based on this, we have calculated the numbers of independent components of representation-matrices for thermal expansion coefficient gensors, piezoelectric coefficient tensors and elastic constant tensors under 31 point-groups for the 1D quasicrystals. Moreover, we have deduced the particular matrix forms of these gensors under the 31 point-groups. This is an important complement of quasicrysgal physical property. 相似文献