摘要:

Transmission electron microscopy has been used to investigate point defect aggregates which were resolvable as dislocation loops in neutron irradiated and annealed molybdenum. The so-called formal analysis was employed in determining the direction and sense of their Burgers vectors. In foils containing a wide spectrum of loop sizes, both vacancy and interstitial type loops have been identified with Burges vectors of the type a/2⟨111⟩.

ISSN:0031-8086    

DOI:10.1080/14786436808218175

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Resistivity and electron microscope measurements have been used to study the effects of deformation on the characteristics of ′ precipitation in an Al 5·12% Cu 0·14% Cd alloy. The deformation was applied both before and simultaneously with ageing. Material subjected to large amounts of deformation (10–60%) before ageing at 180°C, subsequently produced ′ precipitation which obeyed a (time)⅔law. A kinetic analysis gave results which were consistent with ′ precipitation on dislocations, and electron microscopy confirmed this interpretation.

ISSN:0031-8086    

DOI:10.1080/14786436808218176

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The thermoelectric power, S, of a number of palladium and platinum alloys has been measured in the temperature range 2°K to 120°K. For alloys of palladium or platinum with theirneighbouringelements it has been possible to correlate the sign of the diffusion component of thermopower Sdin the residual resistance temperature range with the slope of the density of states versus concentration curves. Furthermore, there is excellent numerical agreement between the observed values of Sd/T and those calculated by a method based on the rigid band model for all the platinum-gold alloys investigated and for the palladium-silver alloys apart from one which contained less than 1 % silver. However, the sign of Sdwas not predicted correctly for a palladium-platinum alloy. Each of the specimens exhibits a large positive phonon drag component of thermopower which persists to high temperatures and is not greatly reduced on alloying. These two features as well as the positive sign are the result of phonon-induced scattering by either s-d or d-d processes.

ISSN:0031-8086    

DOI:10.1080/14786436808218177

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The positional ordering of chain-folds in three polymers is deduced from moiré patterns. In polyoxymethylene and poly(4-methylpentene-1), stacking is mixed, with adjacent re-entry. This is also one alternative for polyethylene, the other being ordered RGI (or RGI') stacking. In either case folds must have restricted geometries and be regular. The occurrence of isolated partial edge dislocations in polyethylene and poly(4-methylpentene-1) and of edge dislocations in polyoxymethylene can be explained as a consequence of fold-surface packing. This explanation requires substantial ordering in as-grown crystals of polyethylene and in crystals of all polymers after annealing. It is suggested that regular folding probably occurs generally in crystals grown from dilute solution but that it may not always be detectable in moiré patterns because of inadequate lamellar contact.

ISSN:0031-8086    

DOI:10.1080/14786436808218178

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A criterion is derived to predict the operative fracture mechanism in the high temperature creep range. The relevance of material properties and test conditions to this criterion is discussed.

ISSN:0031-8086    

DOI:10.1080/14786436808218179

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Magnetic domain patterns on the surfaces of cobalt specimens have been observed directly by scanning electron microscopy. Experiments indicate that the cause of the contrast is the deflection of secondary electrons by the Lorentz force due to the demagnetizing fields near the specimen surface. The scanning electron microscope is likely to become a useful tool in the study of magnetic domain structures.

ISSN:0031-8086    

DOI:10.1080/14786436808218180

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

A model of fatigue crack growth is presented based on the analysis of plastic yield at a notch in terms of dislocations which has been given by Bilbyet al.(1963). This analysis is extended to the case of relaxation of the applied stress, and the reverse plastic displacement at the crack tip is calculated. Reasons are given for equating this quantity with the amount of crack growth, and hence a growth law is obtained. The rate of growth for a specimen of finite width is similarly derived. In both cases, for low stresses, the growth per cycle is proportional to the square of the elastic stress intensity, while for higher stresses, terms involving the fourth and higher powers of stress enter. The model is expected to be applicable to the slip-band type of growth called stage I by Forsyth (1961) and to the ductile component of stage II growth. Although the model is developed only for shear cracks, there are indications that it may be at least approximately applicable to tension-compression fatigue, and we have tested it against several sets of results from this type of experiment. Good agreement for the rate of crack growth per cycle,dc/dn, is obtained over a range of a dozen different materials, provided the value of (1/c)(dc/dn) is greater than about 10−4(where 2c is the length of the crack). There are no adjustable parameters in the theory. The failure of the theory when (1/c)(dc/dn) is less than 10−5is associated with the existence of non-propagating cracks, and it is suggested that the two may be due to the formation of a hard oxide layer at the crack tip. A modified growth law is obtained to account for this effect.

ISSN:0031-8086    

DOI:10.1080/14786436808218181

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

Measurements have been made of the component velocities parallel to and normal to the basal plane of ice growing in supercooled water and aqueous sucrose solutions at supercoolings up to 10°C. It has been found that there are discontinuities in the velocity curves for the sucrose solutions. It is inferred that these are due to a growth mechanism change.

ISSN:0031-8086    

DOI:10.1080/14786436808218182

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The ratio of the twin boundary free energy to grain boundary free energy, δtb/δgb, for coherent twin boundary-grain boundary intersecting systems in thin foils of nickel, TD-nickel, and Inconel 600 has been measured by transmission and diffraction electron microscopy. Final, corrected mean ratios of 0·031, 0·025 and 0·022 for δtb/δgbwere obtained for nickel. TD-nickel and Inconel 600 respectively. Using experimentally measured and estimated values of δgb, the twin boundary free energy δtb, for nickel, TD-nickel and Inconel 600 was observed to be approximately 27, 27 and 19 ergs/cm2respectively.

ISSN:0031-8086    

DOI:10.1080/14786436808218183

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor

摘要:

The Righi-Ledue coefficient in thin polycrystalline aluminium samples has been measured. The size effect predicted by Sondheimer and Blatt has been observed, and the high field value for the Righi-Leduc coefficient is discussed in relation to general theory.

ISSN:0031-8086    

DOI:10.1080/14786436808218184

出版商:Taylor & Francis Group    

年代:1968

数据来源: Taylor