摘要:

In the L12structure, a superdislocation with a ⟨110⟩ Burgers vector may undergo either one of the following basic dissociation schemes:

ISSN:0950-0839    

DOI:10.1080/09500839108205978

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Although Ni3Fe belongs to the group of L12long-range ordered intermetallics the critical resolved shear stress (CRSS) does not depend strongly on the deformation temperature. Dipoles and bundles of dipoles near edge orientations are characteristic features in the dislocation structure. Few screw superlattice dislocations are observed. There are striking similarities to the dislocation structure of pure f.c.c. metals or dilute solid solutions after low and medium plastic deformation.

ISSN:0950-0839    

DOI:10.1080/09500839108205979

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Poor cohesive strength of grain boundaries in strongly ordered Ni3Al is due to porous structure of grain boundaries with crack-like microcavities which open up under small tensile stresses. Interstitial B atoms in Ni-rich Ni3Al reduce the strength of directional bonding between Ni and Al atoms in the interior of the grains. When two such grains with reduced Ni—Al bonding meet each other, the atoms near the grain boundary can relax more easily and the size of the microcavities is reduced. Furthermore, interstitial B atoms increase ductility in the interior of grains so that dislocations can be easily generated to shield the tips of cracks initiated from the cavities, providing increased resistance to intergranular fracture. Evidence for the above mechanism of B-induced strengthening of grain boundaries in Ni3Al is presented.

ISSN:0950-0839    

DOI:10.1080/09500839108205980

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This Letter presents an interpretation of the high resolution electron microscopic observations of the boundary regions of a new long-period tetragonal structure in the Bi-Mn system.

ISSN:0950-0839    

DOI:10.1080/09500839108205981

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The rate of climb of Frank loops of the interstitial type formed in silver during electron irradiation at 130°C in the presence of an external compressive stress has been studied using a combinedin situirradiation/deformation experiment in a high-voltage electron microscope. In the presence of the external compressive stress Frank loops are elongated in the direction nearly perpendicular to the external compressive stress. The results have been compared with those obtained previously but in the presence of an external tensile stress.

ISSN:0950-0839    

DOI:10.1080/09500839108205982

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Fine scale segmentation of screw superdislocations in Co3Ti is shown to arise from the transformation of these into helical dislocations upon electron irradiation. Details of this transformation are analysed under weak-beam conditions.

ISSN:0950-0839    

DOI:10.1080/09500839108205983

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Transient space-charge-limited current for dispersive transport in amorphous silicon has been theoretically investigated, including the multiple trapping process of carriers in a continuous distribution of trap states and the influence of injected carriers upon the electric field redistribution. The results show that for the case of electrode injecting current caused by a step voltage the current before a space-charge-limited transit time is equal towhere μd(t) is the time-dependent drift mobility,qn0, is the density of injected charge, ε is the permittivity,Lis the thickness of the sample,Vis the applied voltage. x1is the leading edge position of the carrier package, which can be expressed asif an exponential distribution of tail states is assumed, where μ0is the band mobility, α is the dispersive parameter andw0is the thermal emission frequency. After a transit time the current decays ast−(α+1)until the final steady-state space-charge-limited current is reached. The transit timetSC, not only depends on the dispersive parameter α but also strongly depends on the injection leveln0and the applied voltageV.

ISSN:0950-0839    

DOI:10.1080/09500839108205984

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Materials of reduced density and increased strength can be achieved by the creation of dispersed voids. A procedure for the manufacture of such materials is described and their characteristic strength estimated.

ISSN:0950-0839    

DOI:10.1080/09500839108205985

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

X-ray K-absorption studies of glassy Ge22Se78and Ge22Se68M10(M = Ag, Cd, In, Pb) have been made in order to understand the nature of bonding of metallic atoms in ternary alloys. The edge shift is found to be dependent on the difference in electronegativity between the metallic atoms and the Ge or Se atoms. The results are in agreement with Pauling's concept of electronegativity and indicate that the nature of the bonds in these glasses is iono-covalent in character as found in many crystalline solids.

ISSN:0950-0839    

DOI:10.1080/09500839108205986

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A double-source evaporator which can be set in the specimen chamber of a high voltage electron microscope has been constructed, With the use of the evaporator, isolated gold clusters of 5 ˜ 10 nm in size were first prepared on a supporting film of amorphous carbon, and then copper atoms were deposited onto the film (and of course onto the gold clusters as well), which was kept at room temperature. Upon the deposition of copper, the gold clusters changed into highly concentrated, homogeneously mixed Au—Cu alloy clusters. The copper atom diffusivity in gold clusters deduced from the present observations is at least 9 orders of magnitude faster than the copper solute diffusion in bulk gold.

ISSN:0950-0839    

DOI:10.1080/09500839108205987

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor