Formation Process of Striation Boundaries of Copper Single Crystals Grown from the Melt

Abstract

Cu (99.999%) single crystals were grown at a rate of 1 mm/min by the horizontal zone melting technique and the effects of the growth direction the dislocation densrty of the seed crystal and the axial temperature gradient on the formation process of the dislocation subboundaries, particularly the striation boundaries, were examined by the observation of the dislocations by the etch pit method.
The results were as follows. The [110] single crystals showed the most remarkable tendency to develop the striations, but the [111] and [100] single crystals were difficult to develop them under normal growth conditions. In the crystal grown under the low axial temperature gradient (20°C/cm), with the low dislocation density seed whose dislocation distribution was homogeneous, the fine network of the subboundaries developed, but the striations did not. On the other hand, in the crystal grown under the same gradient with the seed which contained a fine network of the subboundaries, the striations developed. However, in the high axial temperature gradient (70°C/cm), the striations did not develop, although it was grown with the same seed which developed the striations after growth of one centimeter under a low axial temperature gradient.
From the observations of the change of the arrangement of the dislocations and subboundaries along the growth direction of these crystals, it was considered that the striations were formed by the coalescence of the small angle tilted boundaries which were arranged in parallel and closely.