摘要:

A high temperature stage fitted to a Siemens Elmiskop 1 electron microscope has been used to study directly the annealing of prismatic dislocation loops in thin foils prepared from quenched and aged bulk specimens of aluminium. In the temperature range 170-200°c the loops are observed to shrink and eventually to disappear. Observations on dislocations other than loops also present in the thin foils show that they become smoother while the loops are disappearing. The results are interpreted in terras of climb of dislocations by vacancy emission, and in the case of loops in thin foils, where vacancy supersaturation effects are thought to be negligible, the climb rate is governed by the line tension and curvature of the loops. The radiusrof a loop as a function of timetis given by the theoretical expressionr=r0[1 - (t/τ)]1/2 where τ is the lifetime of a loop of initial radiusr0.The temperature dependence is primarily τ = τ0exp (E/k T) where E is the activation energy of self diffusion. Comparison with experiment gives estimates of the activation energy in the range 1· 2–1 · 3ev.

ISSN:0031-8086    

DOI:10.1080/14786436008241196

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Dislocation loops formed by quenching thin aluminium specimens in iced brine -were studied by the transmission electron microscope technique. As-quenched specimens contained loops 200 Å to 600 Å in diameter with a density of 1016loops per cubic centimetre. Quenched-in loops were completely removed by heating to 200°c for ten minutes or by cold rolling to a 5% reduction in thickness. The disappearance of the loops was accompanied by an increase in the number of irregular kinked dislocation lines.

ISSN:0031-8086    

DOI:10.1080/14786436008241197

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

It is shown experimentally that nitrogen-looking is appreciably stronger than carbon-locking. This is contrary to the customary assumption and it is suggested that there may be chemical as well as elastic interaction with the dislocations. Boron is found to produce even stronger looking than nitrogen. These variations in the locking strength alter the duetile-brittle transition temperature. The stronger the locking, the higher the transition temperature.

ISSN:0031-8086    

DOI:10.1080/14786436008241198

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The mechanism of dislocation loop formation by vacancy condensation is examined in a quantitative manner. The critical vacancy supersaturation necessary for the growth of the loops and the climb rate of the dislocations are determined. It is shown that the mechanism proposed for lineage formation based upon loop growth (Frank, 1956 a) is inapplicable. The number of dislocation loops produced by collapsing vacancy discs is calculated as a function of the cooling rate, cooling range and dislocation density existing in the crystal before cooling.

ISSN:0031-8086    

DOI:10.1080/14786436008241199

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The object of this paper is to estimate, semi-empirically, the Fermi energy of the free electrons in a metal and to indicate why a simple correlation may be expected between this quantity and the electronic work function. Such a straightforward correlation is found to hold approximately for most metals in Groups I to IV of the periodic table.

ISSN:0031-8086    

DOI:10.1080/14786436008241200

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Refinements of the curve of density of statesn(E)inlead, as deduced from the de Haas-van Alphen effect, are inferred from existing superconductivity and transport data on pure lead and on Pb-Tl and Pb-Bi alloys when these data are interpreted in terms of a simple inverse transition metal model.n(E) is found to have a maximum just below the Fermi level. It is suggested that the maximum might be accounted for by supposing the multiply-connected portion of the Fermi surface to split up into separate portions as the electron concentration is reduced; however, this particular interpretation does not seem to be compatible with a model of rigid bands.

ISSN:0031-8086    

DOI:10.1080/14786436008241201

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

High resolution electron microscopy has been used to examine thin films of natural rubber and other polymers. Dispersions of various materials (in particular neoprene and chlorinated natural rubber) in natural rubber have been studied. Structures which are believed to be the individual curled-up molecules of the dispersed polymer have been photographed. Stretched rubber films have also been examined and some information about the mode of deformation obtained.

ISSN:0031-8086    

DOI:10.1080/14786436008241202

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Measurements have been made of the thermal conductivity of germanium, silicon, pure (n= 3 × 1016) indium arsenide and impure (n= 1019) indium arsenide. In each case the electronic contributionKeto thermal conductivity has been calculated and the phonon contributionKLestimated by subtraction ofKefrom the experimental values. The thermal resistance of the lattice has not generally been found to be proportional to the absolute temperature as expected for three-phonon processes but the trend is towards a higher power relationship. The lattice resistance of heavily doped indium arsenide has been found to be greater than that of the pure material.

ISSN:0031-8086    

DOI:10.1080/14786436008241203

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

UNTIL about 1930 there was some doubt as to whether liquid metals showed Hall effects. In 1914, Fenninger failed to find Hall voltages in liquid Hg, but he also found a zero effect in solid Hg and the latter result has been contradicted in at least two subsequent experiments. In 1931, Kikoin and Fakidow showed that a liquid Na-K alloy possessed a Hall coefficient approximately equal to the free electron value of—1/nec, wherenis the number of conduction electrons per unit volume. Nevertheless they too concluded that liquid Hg has zero Hall effect. Taken in conjunction with later results for solid Hg (e.g. those of Serduke and Fisher 1932), this would mean that the Hall coefficient,R, changes considerably on melting. It seemed desirable to check this result in the course of developing apparatus for investigating the Hall coefficient of liquid metals generally.

ISSN:0031-8086    

DOI:10.1080/14786436008241204

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Recently Smallman and Westmacott (1959) observed diffuse scattering of x-rays at small angles in quenched pure metal foils. They attributed the effect to double Bragg scattering caused by distortion due to dislocations formed by condensation of vacancies during quenching. Doherty and Davis (1959) noted that surface oxide on aluminium prevented formation of surface pits which were due to condensation of vacancies. Herein are reported small angle scattering studies of foils (25 to 50 microns thick) of Al and an Al-6 at. % Ag alloy quenched from 540°c indicating that a surface film is effective in increasing the magnitude of the double Bragg scattering; escape of vacancies to the surface is reduced.

ISSN:0031-8086    

DOI:10.1080/14786436008241205

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor