F. W. Young

Bio: F. W. Young is an academic researcher. The author has contributed to research in topics: Dislocation. The author has an hindex of 1, co-authored 1 publications receiving 10 citations.

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

Abstract: 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.

On plastic relaxation of thermal stresses in reinforced metals

Abstract: Silver chloride containing alumina fibers or glass microspheres is used as a model material to study matrix plasticity induced by thermal mismatch in metal matrix composites. Resulting matrix dislocations are decorated at room temperature in the bulk material and observed by optical microscopy. Plastic deformation of the matrix around the inclusions is found to take the form of (i) rows of prismatic dislocation loops puched into the matrix and/or (ii) a plastic zone containing tangled dislocations surrounding the inclusions. From the number of loops punched by spheres, the temperature interval over which slip of prismatic loops is operative is calculated to be 100 ± 30 K wide. The stress in the plastic zone around fibers is determined from the radius of curvature of pinned dislocations, leading to the conclusion that the matrix is locally strain-hardened. A simple model taking this fact into account is proposed to predict the radius of the plastic zone around embedded cylinders and spheres and is compared to the experimental data.

Study of the cellular solidification structure in a continuously cast high purity copper

Abstract: The aim of this paper is to characterize the principal microstructural features of continuously cast high purity copper (99.999 pct Cu), particularly those which might influence high temperature creep. This material contains a cellular solidification structure resulting from impurity segregation due to constitutional supercooling of the melt during solidification. This structure could not be eliminated from the solid copper by thermomechanical treatment. The grown-in structure was studied using optical and electron metallography as well as etch-pitting techniques. In the as-cast material a loose network of dislocation tangles was observed, and in certain locations, preferential etching attack. In addition, small voids were found within the dislocation tangles. Thermomechanical treatment eliminated the dislocation tangles almost entirely, but left locations susceptible to preferential etching attack. At those locations impurities were probably concentrated into zones of a size of a few 1000A. From solubility and concentration considerations, small precipitates (less than 80A in size) or clusters of carbon are suspected.

X-Ray Diffraction Microscopy

Abstract: The individual diffraction spots which are obtained in single crystal transmission or back-reflection x-ray patterns contain a fine structure that can be matched on a point by point basis with the crystal surface appearance and with the internal strain pattern of the underlaying crystal volume. Barrett (1) pointed this out for individual diffraction spots resulting from Laue (transmission) x-ray patterns. Figure 1 indicates the first step which might be taken to further investigate the inner structure of individual diffraction spots, say, as are obtained in a back-reflection photograph of a zinc single crystal. Berg (2) independently demonstrated that detailed structural information could be obtained from an x-ray spot by utilizing a single lattice reflection which satisfied the Bragg equation for characteristic x-radiation under conditions such that very good resolution resulted for the x-ray (back-reflection) picture of the diffracting crystal. This involved placing the crystal at a relatively large distance from the x-ray source so as to achieve a small divergence of x-rays satisfying the Bragg condition and, then, recording the diffracted x-ray intensity at a small distance from the crystal surface so as to minimize the spreading of the x-ray intensity diffracted from any point within the crystal volume. Barrett (3) further demonstrated the potential of this new microscopy in his presentation of the twenty-fourth annual lecture of the Institute of Metals Division of the AIME. For the back reflection geometry, an enhanced x-ray intensity was observed to be diffracted from mildly strained regions of the crystal. Barrett attributed the enhanced intensity to be due both to the greater angular range of x-rays able to be diffracted from a locally strained volume and to the thicker crystal layer able to diffract x-rays if it contains local strains. Near to the time of this latter work by Barrett, quite the reverse x-ray result was found by Borrmann (4) in that an anomalously large x-ray intensity was observed to be transmitted through relatively thick crystals satisfying the (Laue) diffraction condition so long as the crystals were very nearly perfect. Anomalous transmission was said to occur when a transmitted x-ray intensity was detected of magnitude far in excess of that expected from the normal attenuation of the beam due to absorption processes. Thus, anomalous transmission may occur for a transmitted x-ray beam when the product of the crystal absorption coefficient, μ times the crystal thickness, t, is much greater than 1. 0. This property of very nearly perfect crystals being able to anomalously transmit x-rays is explained within the framework of the dynamical theory of x-ray diffraction as given, for example, by von Laue (5).