摘要:

Fractography of a Bi-permeated copper bicrystal was carried out using scanning electron microscopy and reflection electron microscopy. The edges of the main facets, and therefore the indices of the facets were determined by means of reflection electron microscopy. It has been found that the embrittled (118) symmetric tilt boundary is mainly composed of (001), (210), (120) and (071) facets.

ISSN:0950-0839    

DOI:10.1080/09500839008215048

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Misfit dislocations at the interface of a thin epitaxial layer of In0-18Ga0-82As on GaAs have been studied by glancing incidence double-crystal synchrotron X-ray topography. The misfit dislocation density increases dramatically as the layer thickness increases from 17 to 18nm across the sample. Clear evidence for the nucleation of misfit dislocations at threading dislocations from the substrate is presented.

ISSN:0950-0839    

DOI:10.1080/09500839008215049

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

It has been argued that threading dislocations cannot be introduced into heteroepitaxial deposits by the ‘copying’ of emergent substrate dislocations because the Burgers vector of the dislocation must change at the interface. In this Letter it is shown that the extension of an emergent substrate dislocation into the deposit requires the creation of an interfacial dislocation. These three dislocations will meet at an interfacial node where the sum of the Burgers vectors is zero as required.

ISSN:0950-0839    

DOI:10.1080/09500839008215050

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The factors influencing the deformation mechanisms in the intermetallic compounds Al3Ti and Al3V have been studied. As previously reported, plastic deformation of the former compound involves micro-twinning and glide of partial dislocations with Burgers vectorsbgiven by ½⟨110⟩ on {001) producing ribbons of antiphase domain boundaries (APBs). In contrast, for Al3V these mechanisms are not activated and it has been determined that deformation is effected mainly by glide of dislocations withb= ⟨110] on. It is proposed that this difference in behaviour is due to the relative stability of the DO22crystal structure against the Cu3Ti-type structure (micro-twinning) and DO23(APBs on the basal planes). It is suggested that increased ductility in these types of compounds may be realized by alloying with elements which reduce the energy difference between the DO22and Cu3Ti-type crystal structures for these compounds.

ISSN:0950-0839    

DOI:10.1080/09500839008215051

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Weak-beam observation electron microscopy has been performed onsuperlattice dislocations lying on theprism planes in Ti3Al single crystals deformed at room temperature. The dislocations observed are mostly of edge character. They are found to dissociate into four partials on the prism plane; a superdislocation into two unit dislocations with an associated antiphase boundary in between and the latter again into partials bounding a complex stacking fault.

ISSN:0950-0839    

DOI:10.1080/09500839008215052

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

First-principles total-energy calculations of the elastic constants and shear fault energies of TiAl are presented. We find a large elastic-shear anisotropy along the [011] direction, and high antiphase-boundary energies due to the strong cohesion between Ti and A1 layers as well as the formation of directional d bonds in the Ti layer. Shear faults of intrinsic type, extrinsic type and twin boundary type are predicted to be prevalent owing to their low energies. The anomalous temperature dependence of the flow stress is explained by the cross-slip-pinning and fault-dragging mechanisms. The intrinsic brittleness of TiAl is discussed in terms of these results.

ISSN:0950-0839    

DOI:10.1080/09500839008215053

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A sharp increase in the number of dislocations threading from the heterointerface to the growth surface has been observed when the Ge content is increased (and consequently the critical thickness decreased) at about x=0·4 in GexSi1−xsingle epilayers grown on (100) Si. This increase by a factor of 60 times seems to be due to the change in glide behaviour of epithreading dislocations associated with interfacial misfit dislocations with thickness. The threading density difference persists in layers of equal thickness but differing Ge content to thicknesses well above critical.

ISSN:0950-0839    

DOI:10.1080/09500839008215054

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A single-crystal X-ray structure analysis of decagonal Al65Cu20Co15has been performed using then-dimensional approach. The structure has been solved by Patterson analysis and subsequent least-squares refinement, both in the five-dimensional description. A final value ofwR=0.097 for 259 independent reflections was achieved withI≥2σ(1)and 12 variables. There are three atoms in the asymmetric unit. The calculated density of the refined, structure model is ρc= 4.8 M gm−3. The three-dimensional decagonal structure consists of two planar quasiperiodic layers, related by the tenfold screw axis, stacked periodically one upon the other. Characteristic large elements of the crystalline Al13Fe4structure type can be found in new combinations in the quasiperiodic layers. It is remarkable that pentagonal channels appear which are empty or occupied statistically.

ISSN:0950-0839    

DOI:10.1080/09500839008215055

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

X-ray powder diffraction peaks have been measured for melt-spun and annealed Al-Cu-Fe quasicrystals. From the change in width and position of the diffraction peaks it was found that the linear phason strain introduced by melt-quenching is removed by a 1 h isochronal anneal between 873 and 1093 K.

ISSN:0950-0839    

DOI:10.1080/09500839008215056

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A high-energy permanent magnet, whose nonmagnetic structure belongs to the space group P6/m mm, has been used to study the magnetic effect on symmetry determination by convergent-beam electron diffraction (CBED) patterns. At the [0001] zone axis, along which the magnetization of the domains is aligned, the symmetry of CBED patterns remains 6mm as if the specimen were nonmagnetic. However, at thezone axis, the mirror planes contained by thecaxis were absent in the zero-order disks even though the whole pattern appeared to have 2mm symmetry. By looking into the interaction between the electron beam and the magnetic field produced by the specimen, it was found that the magnetic effect of the specimen was zero in the first-order approximation when the electron beam was along the [0001] direction, and was maximized when the electron beam was parallel to the basal plane. The apparent 2mm symmetry in the whole pattern ofzone axis indicates that diffraction is overwhelmed by the Coulombic potential in the specimen.

ISSN:0950-0839    

DOI:10.1080/09500839008215057

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor