摘要:

An Al—Mn—Cr—Si alloy, rapidly solidified by means of melt-spinning in a moderate vacuum, has been studied by transmission electron microscopy. The material is found to consist of fine icosahedral quasicrystalline precipitates in an aluminium matrix. Electron diffraction patterns and high-resolution electron microscopy show a high degree of coherence between the quasicrystals and the matrix giving a strict orientational relationship. Coherence strain between the particles and the matrix is found on both sides of the interface. In the quasicrystal the strain is seen to distort the structure, changing it locally. This is verified by Fourier transforms of the observed images. The transforms can also explain the changes in period and in direction of moiré fringes found between the matrix and the precipitates. On the aluminium side of the interface a periodic strain is observed. This period may be ascribed to the small difference between the Al (200) planes and the (110000) quasi-lattice planes spacings.

ISSN:0950-0839    

DOI:10.1080/09500839108205988

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In an inhomogeneous elastic medium, where the elastic constantsCijkldepend on position, a straight dislocation feels a self-force. Ifb(Cijkl, (x))bis the prelogarithmic energy factor for a dislocation in an infinite homogeneous medium withCijkl= Cijkl(x) everywhere, the leading term in the self-force isF=b(ε)bIn |εb(ε)b/bb| with ε being a core radius.

ISSN:0950-0839    

DOI:10.1080/09500839108205989

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A novel type of dislocation in YBa2Cu3O7, has been identified and analysed by high resolution electron microscopy. Non-stoichiometry is accommodated by means of Frank type sessile dislocations. In the double CuO layers, resulting from the insertion of an extra CuO layer, sometimes a 90° reorientation of the chains occurs along the layer plane. This orientation change of the double chain can be described as being caused by the propagation of a dislocation with a 1/2 [110] Burgers vector and a (001) glide plane located between the two CuO layers, accompanied by reshuffling of part of the oxygen ions.

ISSN:0950-0839    

DOI:10.1080/09500839108205990

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

T2phase within αAlTe2eutectic dendrites in chill-cast Al—15 wt% Li—6 wt% Cu alloy exhibits distortion from the ideal icosahedral pattern consistent with formation of growth twins with a common fivefold axis. Similar displacements are observed for primary T2in Al—Li—Cu and for icosahedral phases in rapidly solidified Al—Mn and Al—Fe—Cu. The correlated nature of the observed reciprocal lattice displacements and the long range lattice displacements suggest that the defects are a true reflection of the state of the material rather than an artefact generated by specimen preparation.

ISSN:0950-0839    

DOI:10.1080/09500839108205991

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

La structure atomique du joint de macle Σ3 (111) de la phase L12Ni3, (Al, 8 at.% Nb) est observee en microscopie électronique à haute résolution. Des calculs d'images multislices indiquent que cette structure est plus complexe que celle observée antkrieurement pour le měme joint dans d'autres matériaux c.f.c.: le plan d'interface n'est pas un plan miroir pour les sites atomiques.

ISSN:0950-0839    

DOI:10.1080/09500839108205992

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The stability of the decagonal phase of Al65Cu15, Co20(d phase) has been studied through thermal annealing, electron beam irradiation and recovery experiments using X-ray and electron diffraction techniques. Long-term annealing of as-cast and melt-spun samples over the temperature 940 to 550°C did not show a decagonal-to-crystalline phase transformation. Upon electron-beam irradiation, the d phase transformed to a f.c.c. phase witha= 351 Å, and the d phase was recovered by heating the f.c.c. phase to 600°C. A simple cubic (s.c.) phase witha= 2.87 Å was found in thin-film samples slightly off the d phase composition, and it transformed partially to the d phase at 600°C. At high temperature (∼900°C), the d and s.c. coexist in the off-composition thin-film and melt-spun samples. Implications of our results on the stability of decagonal Al—Cu—Co are discussed.

ISSN:0950-0839    

DOI:10.1080/09500839108205993

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Many-body, long-range potentials of a Finnis-Sinclair type are formulated for the atomistic description of binary f.c.c. metallic alloys. These potentials are generalizations of the scheme constructed by Sutton and Chen (1990), for the atomistic modelling of f.c.c. elemental metals. The parameters for the alloy potentials are obtained directly from the parameters for the elemental metals, without any further adjustable fitting. Lattice parameters, elastic constants and enthalpy of formation of 45 binary, random f.c.c. alloys are calculated.

ISSN:0950-0839    

DOI:10.1080/09500839108205994

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Contrary to generally-held views, 180° magnetic domain walls lying in the cube planes normal to (001)-orientation single-crystal plates of Fe + 3wt%Si can be detected by diffraction contrast on X-ray projection topographs by use of conventional experimental arrangements. Conditions for good observations are explained with illustrations. The dominant contrast appears at intersections of the 180° Bloch walls with the X-ray exit surface of the specimen and is generated by small localized deformations at these outcrops. The contrast is at best very weak, being only about 10−2of that generated by 90° domain walls.

ISSN:0950-0839    

DOI:10.1080/09500839108205995

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A structure analysis has been carried out on the nucleus formed in amorphous Ge films at the initial stage of crystallization by means of high resolution electron microscopy. Small crystallites displaying fivefold symmetries were formed in the amorphous matrix with sizes down to about 10 nm. A columnar structure model for the nuclei which consists of five-membered rings, stacking with a common axis, has been proposed and the computer-simulated electron microscope image produced, based on this model, is in good agreement with the observed images. The results suggest the existence of pentagonal structural units in amorphous germanium which play a salient role as preferential nucleation sites at the stage of incipient crystallization.

ISSN:0950-0839    

DOI:10.1080/09500839108205996

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Computer images of electron diffraction contrast from 90° wedge specimens containing strained III-V compound heterostructure layers are compared with experimental TEM images. The image contrast in the wedge is strongly affected by strain relaxation near the edge and allows unambiguous derivation of the bulk strain. The strain distributions used to simulate diffraction contrast are obtained by finite-element calculations. This new technique combines high spatial resolution with a high sensitivity (∼0.01%) for changes in the strain value. It also has the advantage of speed in the sample preparation.

ISSN:0950-0839    

DOI:10.1080/09500839108205997

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor