Substructure control by solidification control in cu crystals

Abstract

In an attempt to systematically control dislocation substructure, seeded <111>Cu single crystals have been grown from the melt at rates from 1.1 to 730 cm/h. Soft and hard graphite molds are used, with the hard molds surrounded by graphite or firebrick sleeves. In this fashion mold wall characteristics are varied and mold thermal conductivity is changed from 27×10⁻⁴ to 0.29×10⁻⁴ (cgs units). An increase in growth rate over this range has little effect on random dislocation density, which remains about 1.5×10⁶ cm⁻². The increase does cause a decrease in dislocation cell size from about 5×10⁻² to 0.5×10⁻² cm. The decrease varies approximately as (freezing rate)^−1/2 in agreement with the dislocation half-loop model of dislocation generation. An increase of mold thermal conductivity of a factor of 100 has little effect on random density, but causes a 50 to 300 pct increase in cell size. Crystals grown in soft molds have a random density about one-half those grown in hard molds. The cell size is comparable to that obtained with firebricked-sleeved hard molds of similar thermal conductivity. The data indicate that solute effects do not play a significant part in substructure generation in copper of 99.999 pct purity.