摘要:

In rapidly solidified Al—Cu—Mn alloys, the quasicrystalline phases (icosahedral and decagonal) are metastable. In this Letter, the transitions of the icosahedral (i) and decagonal (d) phases towards the equilibrium periodic phases have been studied by means of differential thermal analysis, X-ray diffraction and transmission electron microscopy. The nature of the crystalline phases formed on heating was in agreement with the equilibrium phase diagram (Kösteret al. 1966). Evidence is shown of a hierarchy of stability between the i and d phases: on heating, the i phase is transformed into the d phase.

ISSN:0950-0839    

DOI:10.1080/09500839108215114

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Stacking-fault double-ribbons have been observed in GaAs; a compound semiconductor. Values for the extrinsic and intrinsic stacking-fault energies of 41·2±5 mJm−2and 46·5±6 mJm−2, respectively, were obtained from the widths of the stacking-fault ribbons. The ratio of the intrinsic to extrinsic stacking-fault energy is found to be 1·13±0·08.

ISSN:0950-0839    

DOI:10.1080/09500839108215115

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The first experimental results on the avalanche breakdown electric field of p-doped germanium single crystals with different acceptor concentrations are outlined. The critical field strength turns out to increase linearly with increasing concentration of the doping acceptors. We briefly discuss the relevant scattering processes in terms of simple hot-carrier model considerations.

ISSN:0950-0839    

DOI:10.1080/09500839108215116

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In this letter we study nonlinear irreversible mechanical properties of crumpled wires in a large interval of deformations. Power laws connecting the geometrical and mechanical variables for this kind of disordered system are examined. Critical exponents are obtained from experiments and from scaling arguments. The behaviour of crumpled wires and crumpled surfaces are compared.

ISSN:0950-0839    

DOI:10.1080/09500839108215117

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Implications are investigated of a deformation mechanism founded on the idea that kinks on screw dislocations are capable of transporting Kear—Wilsdorf configurations. In this mechanism, which takes into account microstructural features observed experimentally, Kear—Wilsdorf configurations need not transform into a glissile core prior to movement, as envisaged in previous treatments. The total friction stress that should be overcome in order to activate kink slip depends upon kink distribution; this stress is shown to increase as the bending of Kear—Wilsdorf configurations in the cube plane increases. The consistency between the present kink dragging mechanism and selected mechanical properties of L12, alloys is discussed.

ISSN:0950-0839    

DOI:10.1080/09500839108215118

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A transition to a higher electrical-conduction state is observed at temperatures between 30 K and 115K in graphite-vaporized films, depending on preparation conditions. This transition may be related to carbon clusters [Cn, withn= 30–100] being contained in graphitic amorphous carbon.

ISSN:0950-0839    

DOI:10.1080/09500839108215119

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In a recent paper on transient space-charge-limited currents for electrons (Yanet al. 1991) it was predicted that the dispersive transit time under strong carrier injection can be ten times smaller than under weak carrier injection. Because this is potentially such an important result, the basis for the decrease was examined carefully. We found that the predicted decrease resulted from the unphysical condition that the electric field at the injecting contactC(t)was allowed to be positive under strong electron injection. When the electric field at the injecting contact was restricted to negative values, no sharp drop in transit time is found.

ISSN:0950-0839    

DOI:10.1080/09500839108215120

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Conventional transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM) experiments have been carried out on thermally-aged binary Fe 1·30 wt% Cu and ternary Fe 1·28 wt% Cu 1·43 wt.% Ni alloys to study the structure of small (7–15 nm) copper precipitates in the α-Fe matrix. The experiments show that the precipitates have a twinned 9R close-packed structure, rather than the expected f.c.c. structure. It is believed that this structure is generated initially by a martensitic transformation from the metastable b.c.c. phase.

ISSN:0950-0839    

DOI:10.1080/09500839108215121

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A Monte Carlo simulation method for the calculation of the frequency-dependent electrical conductivity and the associated time correlation function is illustrated for a two sublattice vacancy migration model, and some discrepancies with current kinetic theories are observed. The method should be of wide utility for atom hopping models in determining the frequency dependence of transport coefficients and in the calculation of time correlation functions which provide additional tests of kinetic theories of both the static and the frequency-dependent transport coefficients.

ISSN:0950-0839    

DOI:10.1080/09500839108215122

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A crystal-to-decagonal quasicrystal transformation in an Al63Cu17·5Co17·5Si2alloy has been produced by smooth electron beam irradiation heating. HREM observations of both states allow the determination of the characteristics of the decagonal quasilattice. Phasons are considered in order to interpret such a transformation.

ISSN:0950-0839    

DOI:10.1080/09500839108215123

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor