F. W. Young

X‐Ray Topographic Study of Tensile Deformation in Nearly Perfect Copper Crystals

Copper crystals of a cross section 0.5×0.1 cm and of an initial dislocation density N 50–5000 cm/cm3 were deformed in tension, and Borrmann x‐ray topographs were taken after successive stress increments. All dislocations were observed and Burgers vectors determined. Stereo pairs were made. The grown‐in dislocations were moved very little by the applied stresses. For crystals of lower initial N most of the dislocation generation could be related to localized stresses in the grip regions, while in the crystals with higher initial N the generation probably was related to grown‐in dislocations. Slip bands were formed; neither the source nor the generation mechanism of dislocations in these bands was determined. Screw dislocations were left by edge segments running across the crystal. These screw dislocations cross slipped frequently at stresses of a few grams/mm2, and this process tended to fill the volume of crystal between the bands with dislocations. By counting all new dislocations the shear strain was co...

Growth of dislocations during laser melting and solidification

Silicon crystals containing dislocations which terminated in the free surface were melted to depths of about 0.5 μm by rube‐laser pulses, and the growth characteristics of dislocations of various types were studied by transmission electron microscopy. It was found that both edge‐ and screw‐type dislocations grew in 〈113〉 directions that were not normal to the crystal‐growth interface.

Burgers Vector of Dislocations Generated by Small Stresses in Copper Crystals

In an x‐ray topography study of the deformation of copper, the dislocations which were generated during the beginning stage of deformation were determined by the external geometry of the crystal in addition to the usual requirements of the maximum resolved shear stress.

Effect of Neutron Irradiation on Copper Crystals at High Temperatures

Etching, x‐ray topography, and electron‐microscopy studies have shown that neutron irradiation at about 400°C produces a defect structure different from that produced by irradiation at ambient temperatures. On a macroscopic scale the damage was nonhomogeneous; there were regions containing high concentrations of defects separated by apparently perfect crystal. The size of the defect regions ranged from 10–100 μ, and the distance between regions was ∼100 μ. Borrmann topographs showed long‐range order among the defect regions in that they tended to be aligned in habit planes parallel to (111) planes. Measurements of the absolute integrated intensities of Borrmann diffracted beams indicated that there must have been a large degree of elastic strain between defect regions. It has been shown that the defect regions were aggregates of large dislocation loops 1000–2000 A in diameter, dislocation tangles of roughly the same dimension, smaller loops 50–150 A in diameter, and three‐dimensional point defect clusters...

Investigation of Fast‐Neutron Radiation Damage in Nearly Perfect Copper Crystals by X‐Ray Diffraction Techniques

The effects of fast‐neutron irradiation at about 40°C in nearly perfect copper crystals have been examined by x‐ray diffraction techniques. Anomalous x‐ray transmission (Borrmann) and Bragg reflection geometries were used to investigate the changes in diffracted intensities caused by defects produced by the neutron irradiation. Both Borrmann and Bragg peak intensities were reduced to values significantly below those for perfect crystals, and the reduction in the Bragg intensities was accompanied by a large increase in the diffuse scattering in the wings of the peak. It is shown that isolated point defects and the distortion associated with them would not account for the changes in x‐ray intensities. Annealing studies indicated that both vacancies and interstitials were present in these crystals after irradiation, and all of the damage was removed by annealing at 500°C.

Effect of temperature on irradiation‐induced dislocation loops in copper

The effect of irradiation temperature on irradiation‐induced dislocation loops in copper has been studied by x‐ray diffuse scattering. Dislocation loop size distributions and total defect concentrations were obtained for irradiations in the temperature range 316–483 °K for neutron doses in the range (1–10) ×1018 n/cm2. The average loop sizes were found to increase with increasing irradiation temperature and increasing neutron dose. The number of point defects stored in the loop distributions tended to saturate at the higher doses and were found to decrease with increasing irradiation temperature. Ambient‐temperature measurements made on 4 °K neutron‐ and electron‐irradiated copper indicated the dislocation loops formed during the anneal to room temperature were smaller than those produced by ambient‐temperature reactor irradiations.

Study of Certain Strain Centers in Copper Crystals by Etch‐Pit and X‐Ray Techniques

Strain centers with attendant prismatic dislocation loops have been studied in copper crystals of low dislocation density by use of Borrmann x‐ray topograph and etch‐pit techniques. Direct comparison of these defects with the two techniques showed an exact correlation. While the nature of the centers of the strain could not be certainly determined, there was evidence that the loops were of the interstitial type.

Observations of Dislocations in Copper using Borrmann Transmission Topographs

Using the Borrmann diffracted beams for Ag Kα radiation, x‐ray topographs have been made of copper crystal plates 1 × 1 × Z cm, Z ≦ 0.1, with (111) faces. Dislocation lines were generally recorded as lines of less intensity on the x‐ray plate. Both annealed and neutron irradiated crystals were investigated. In the latter the dislocations were pinned and were not moved by the small stresses accidently imposed while making the topographs; and dislocation arrangements in the bulk crystal were determined. The Burgers vectors were deduced from {111} topographs, employing the condition that for no contrast g· b = 0. For edge dislocations, the additional condition g × n = 0 was necessary for no contrast, and it was demonstrated that this type of contrast was more pronounced for dislocations grouped in a slip trace. It was found that dislocations could be seen all the way through crystals for Z = 0.06 cm. A semiquantitative correlation has been established between etch pits formed at dislocation sites on the (111...

ANOMALOUS TRANSMISSION OF X RAYS IN COPPER CRYSTALS

The anomalous transmission of x rays in nearly perfect copper crystals is reported. The apparent absorption coefficient of x rays becomes abnormally small when an incident beam undergoes a Bragg reflection during passage through the crystal. The incident radiation was Cu K alpha /sub 1/ monochromated by (111) reflection from a perfect silicon crystal on to the 1 cm/sup 2/ face (110) of thickness 0.05 to 1.3 mm. Apparent individual imperfections are revealed as light images in the transmitted beam image. (C.E.S.)

A Comparison of Diffuse Scattering by Defects Measured in Anomalous Transmission and Near Bragg Reflections

The diffuse scattering from neutron-irradiation-produced defects in copper was measured in anomalous transmission and near the 111 Bragg reflection. The results were related through the theory of Dederichs, and the intensities and forms of the scattering curves obtained from the two measurements were found to be in good agreement over a wide range of defect concentrations and sizes. It was shown that the intercept of a plot of the diffuse scattering intensity Is (q0) vs In (q0) is at q0=e1/2/R for defects of uniform radius R and at q0 ≌1/R0 e for an exponential size distribution of average size R0 .