ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01345.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe projection method is the current basis of numerous research for structural models of quasicrystals. The method provides structures which are quasiperiodic and present an icosahedral symmetry, and allows a simple computation of their Fourier transforms. The two‐dimensional projections of the structures can also be obtained by the same method and are quasiperiodic and discret

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01346.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe Penrose tiling is indeed a geometrical model appropriate for the description of the phenomena of icosahedral quasicrystals, although it is probably a related example, rather than the central theory itself, but many aspects of the theory remain to be developed. The transition from X‐ray crystal structure analysis (XRCSA) to high resolution electron microscopy (HREM) as the paradigmatic method for the investigation of crystal structures has facilitated this development and promises other advances from classical crystallograph

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01347.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYAl‐Mn‐Si icosahedral and Al‐Mn decagonal quasicrystals have been studied by high‐resolution electron microscopy. High‐resolution micrographs of the Al‐Mn‐Si icosahedral quasicrystal taken with the incident beam along the five‐, three‐ and two‐fold symmetry axes are well interpreted on a three‐dimensional Penrose tiling model. An image of the Al‐Mn decagonal quasicrystal with the incident beam parallel to the ten‐fold symmetry axis shows a pattern of an aperiodic tiling with two types of rhombs which can be distinguished from the Penrose tiling using matching and inflation rules. The Al‐Mn decagonal quasicrystal examined coexists coherently with that of icosahedral symmetry exhibiting a definite crystallograph

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01348.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe morphology of the icosahedral phase in Al86Mn14alloy has been observed as flower‐like and of granular shape by TEM. These two kinds of morphologies may be regarded as the different sections of a three‐dimensional flower‐like grain. Inside these grains, a fine substructure of a few nm in size has been found. A dendritic morphology with a diffraction pattern showing five‐fold symmetry have also been observed in the Al86Mn14alloy. On the basis of these observations, a model based on nucleation, growth and aggregation has been proposed to explain the formation process of the quasicrystallin

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01349.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe inherent differences between the various current structural models for the determination of the scattering behaviour of icosahedral materials are reviewed with the conclusion that the nature of their apparently characteristic inhomogeneity needs further clarification. Here it is shown that the dark field reflection and deviation parameter dependence of transmission electron microscope (TEM) contrast variations can be used to provide useful qualitative evidence for the nature of quasicrystal inhomogeneities. Results obtained using the technique are discussed for the icosahedral phases i‐(AlMn) and i‐(A

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01350.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYElectron microscopic observations on the morphology of icosahedral and decagonal quasicrystals in aluminium‐manganese alloys have been interpreted in favour of a heterogenous nucleation mode. The transition of icosahedral quasicrystals from nonfacetted dendrites to facetted particles occurs as a function of composition. While the variety of electron diffraction patterns to be expected from icosahedral quasicrystals has been demonstrated for a number of alloys, subtle intensity differences exist among analogous patterns from Al‐Mn, Al‐Cr, Al‐Mn‐Si and Mg‐Al‐Zn‐Cu alloys. Electron diffraction patterns from decagonal quasicrystals can be understood on the basis of an edge‐centred icosahedron as opposed to a vertex‐centred icosahedron for icosahedral quasicrystals. Truncation from two‐dimensional quasi

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01351.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe potential interrelationship between the Al‐Mn μ phase and icosahedral structures is investigated by a systematic study of the electron diffraction behaviour of the crystalline phase. The presence of systematic absences in selected area diffraction patterns is used to propose a space group for the μ phase and similarities with the icosahedral and decagonal diffraction patterns are argued to imply the presence in both the crystalline and quasicrystalline phases of icosahedral units with different stacking arrangeme

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01352.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYAfter heating to 400°C, the icosahedral quasicrystal in (Ti1‐IVI)2Ni alloys displays a kind of local or short range translational order as evidenced by a more or less commensurate arrangement of electron diffraction spots along one or several twofold directions. This is supported partly by a high resolution electron microscopic image which shows, in some parts of it, a somewhat regular arrangement of bright points. A structural model with some short‐range translation order in the range of a few nanometres along one of the fifteen twofold directions in the icosahedral matrix has been proposed and its optical diffraction pattern is in good agreement with the experimental observat

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01353.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYWe have observed the formation of icosahedral quasicrystals of Al‐Mg‐Zn, Al‐Mg‐Cu, Al‐Li‐Zn and Al‐Li‐Cu by low temperature annealing of solid solution alloys. The icosahedral phase particles form at the grain boundaries of the matrix alloys. The orientational relationships between the icosahedral crystallites, their corresponding Frank‐Kaspar phase particles and the aluminium matrix are reported. The stability of the icosahedral phases is also discussed. Finally, the importance of grain boundary icosahedral phase particles to the physical properties of commercial aluminium allo

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1987.tb01354.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY