발간논문

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The diffusion of carbon through the surface of iron powders in the case of iron-graphite compact was studied for a certain desired carbon content after sintering under a constant stamping pressure. The necessary sintering time for high purity of graphite to diffuse perfectly into bulk of iron powder coincided satisfactorily with the calculated value from the mathematical analysis performed by Choi. The practically necessary sintering time is however smaller gradually than that obtained from the mathematical analysis as the grain size of Iron powder is smaller. The kinetics of diffusion of carbon atom through and at the surface of Iron powder was discussed theoretically.

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Dislocation etch pits of zinc single crystals grown by modified Bridgman method were studied using etchants of Gilman. The effects of deformation and heat treatment on the substructure of etch pits were also investigated. Elongated cell structures, which were observed by Kratochvil and Sichovla were not found from the as grown crystals. But nonelongated cell structures were detected occasionally. The secondary substructures following homogenization of segregated impurities were not found. Annealed samples have shown grown subgrains and also secondary substructures. Some samples were deformed (bending) at 100℃ or 180℃ during the slow cooling following annealing, and proceeded further slow cooling until it reached room temperature. The substructures which were induced through deformation, were found but not the secondary substructures. With the samples, which were annealed at about 300℃ after deformation, deformation-induced substructures were not found mostly. But greatly grown secondary substructures were found. With the deformed crystals the growth of secondary substructures through heating were more enhanced than undeformed ones.

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Using a scratch smoothing technique, the magnitude and the ratio of the surface diffusion coefficients (D_s) in two orthogonal directions have been measured on copper for over (100) different surface orientations. Anisotropy was found for all surface orientations except those lying near the (100) and (111); however, these anisotropies were rarely greater than 2.0. The direction of maximum D_s appears to coincide with the direction of step edges on any given surface, and if no such steps exist, no anisotropy is found. Thus the jump frequency along a step edge is shown to be faster than the frequency of a jump over the step. The values of D_s and ΔH for the (100) and the (111) orientations agree quite well with those obtained earlier by the grain boundary grooving technique. It is proven that the directions of maximum and minimum D_s(the principal axes) for any surface orientation are known if the perfectly ordered plane corresponding to the given surface orientation possesses a plane of mirror symmetry. Thus the principal axes of D_s for orientations lying along the sides of the unit stereographic triangle are always known independent of the extent of thermal disorder or impurity adsorption. The merits and shortcomings of king and Mullins recently published equations relating D_s to the rate of scratch smoothing are discussed.

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