ISSN:0021-8979    

DOI:10.1063/1.1735202

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The effect of introducing point defects into pure metals by (a) quenching and (b) irradiation has been studied using the small‐angle x‐ray scatter technique. Scattering was obtained from both quenched copper and aluminum after appropriate ageing treatments, from &agr;‐irradiated copper after annealing, and from neutron‐irradiated copper. The source of scattering has been considered in each case.Direct observation of the scattering defects has been obtained for the quenched, neutron‐, and &agr;‐irradiated metals using thin film electron transmission microscopy. The quenched copper and aluminum contain dislocation loops of the order of a few hundred angstroms diameter formed by the condensation of vacancies, while the &agr;‐irradiated metal contains small cavities. Some additional electron microscopic studies of quenched silver and gold are also mentioned and the results discussed in relation to the mechanical and physical properties of quenched metals. No direct evidence has yet been found in neutron‐irradiated copper (because of the difficulties in electropolishing), but the small‐angle scattering when considered with mechanical property measurements strongly suggests the existence of small ``regions'' ∼100 A diameter. Direct observation of ``damage'' in neutron‐irradiated aluminium is observed, however, and shows the existence of dislocation loops, ``jogged'' dislocations, and ``spiral'' dislocations in agreement with theoretical predictions.

ISSN:0021-8979    

DOI:10.1063/1.1735203

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The small angle scattering of x‐rays from single crystals of magnesium plastically deformed in simple shear has been measured in the angular range of 4′ to 5°. The crystals were subjected to both unidirectional and cyclic shear stresses applied along the [112¯0] direction. Thin slices of the deformed single crystals were prepared using strain‐free cutting and polishing techniques. The thin slices had orientations such that the slip direction was either parallel or perpendicular to the incident x‐ray beam in order to observe any anisotropy in the scattering that might be due to dislocations. It was found that those samples which contained deformation twins within the irradiated volume produced rather large scattered intensity. This scattered intensity is interpreted as being due to double Bragg scattering. The scattered intensity from other specimens was attributed to surface scattering. No evidence for small angle scattering by dislocations was found.

ISSN:0021-8979    

DOI:10.1063/1.1735204

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The theory of double Bragg reflections in single crystals is derived on both a kinematical and dynamical basis. Experiments are reported using single crystals of LiF, diamond, aluminum‐copper, pentaerithritol, and stilbene, and comparisons made with the theory.

ISSN:0021-8979    

DOI:10.1063/1.1735205

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

It is shown that in spite of the occurrence of double Bragg scattering effects small angle scattering of x‐rays from dislocations in cold‐worked crystals should be observable, provided face‐centered cubic crystals deformed in tension at low temperature are used. In stage II of the stress‐strain curve the dislocation arrangement is essentially that of piled‐up groups. The small angle scattering from such groups has been worked out, treating both the first‐order (linear elastic theory) and second‐order (nonlinear elastic theory) effects. The first‐order effect dominates if the scattering vectorgis normal to the glide‐plane, whereas the second‐order effect dominates ifglies in the glide‐plane. If both effects can be observed, interesting information on the density and the arrangement of dislocations can be derived.

ISSN:0021-8979    

DOI:10.1063/1.1735206

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

X‐rays or thermal neutrons may be scattered at small angles from deformed metals due both to ``true'' small‐angle scattering and to double Bragg reflections. These two effects are discussed theoretically and compared to see how one may be distinguished from the other in the results of experimental observations. Experiments are described on the small‐angle scattering of x‐rays from polycrystalline copper and single grains of aluminum deformed by cold‐work or fatigued in pulsating tension. The results show in a direct and conclusive way that almost all of the scattering is due to double Bragg reflections. No surface scattering has been observed. Double Bragg reflections have been eliminated in experiments on the small‐angle scattering of cold neutrons from cold‐worked and fatigued copper and aluminum. The results, which indicate the magnitude of the ``true'' scattering, are consistent with scattering from dislocations. Hence there is no direct evidence of the existence of cavities in cold‐worked or fatigued metals as the result of small‐angle scattering experiments with either x‐rays or neutrons.

ISSN:0021-8979    

DOI:10.1063/1.1735207

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The scattering of x‐rays at small angles from polycrystalline copper is found to increase when the recrystallized metal is bombarded with fast neutrons. The observed effects above 2° are due to double Bragg reflections; below about 1½° they can be explained in terms both of double reflections and ``true'' small‐angle scattering. The results indicate that either small coherent regions (of diameter about 100 A) or severe strains are present in the irradiated metal. The results are consistent with other measurements (particularly of mechanical properties) on irradiated metals.

ISSN:0021-8979    

DOI:10.1063/1.1735208

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Various explanations have been put forward to account for the low angle x‐ray scattering from cold worked metals. The experimental results obtained by an examination of individual grains of polycrystalline fatigue specimens indicate that double Bragg reflection plays an important role in this phenomenon. The fatigue process resulted in the formation of subgrains, the misorientations within a grain amounting to 15°.

ISSN:0021-8979    

DOI:10.1063/1.1735209

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The characteristic small angle x‐ray scattering from cold worked polycrystalline foils of Cu, Al, and Ni is found to appear immediately when the foil is stretched in the x‐ray beam at liquid air temperature. The scattering at a fixed angle is a reversible function of foil temperature as long as recrystallization temperatures are not exceeded. The temperature dependence is about twice that expected from the Debye temperature factor of an average Bragg reflection. It is postulated that the small angle scattering is the result of two successive Bragg reflections from two slightly misoriented subgrains of the same grain. The small angle scattering is found to be polarized. This can be understood only on the double Bragg scattering model. The double Bragg model was suggested by our observation of occasional isolated small angle peaks from annealed foils. These have unusual characteristics which quickly eliminate any possible single scattering source. They are double scattering from two large annealed grains which sometimes accidentally satisfy all the orientation requirements.

ISSN:0021-8979    

DOI:10.1063/1.1735210

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Observations of x‐ray scattering from deformed and undeformed metal foils using an evacuated film chamber give evidence of double Bragg reflections. Experiments have been done on single crystals and polycrystalline foils of aluminum and copper and also on an annealed powder sample of copper. The scattering was measured in the angular range from 1° to 50° and agrees very well with theoretical considerations of expected double reflection effects in different states of deformation. Diffraction by lattice defects in the deformed state cannot be observed because its intensity is too small in comparison to that of double reflections.

ISSN:0021-8979    

DOI:10.1063/1.1735211

出版商:AIP    

年代:1959

数据来源: AIP