Single crystals of [111] orientation were grown by pulling from the melt at 1.7 x 10-5m/s, using a rotation rate of 1rad/s, in a stream of pure Ar. The density and distribution of dislocations in the crystals was investigated by using an etching technique. It was found that small additions of Al suppressed the formation of slip dislocations, as well as the frequent increase in dislocation density which occurred from the center to the periphery in pulled Cu crystals. The mean dislocation density had a minimum value of about 5 x 107/m2 at an Al content of 0.1at%. This was more than an order of magnitude less than that in Cu crystals. However, sub-boundaries and dislocation clusters were sometimes introduced into crystals which contained 0.05 to 0.5at%Al. These were similar to those which were found in dilute Cu-Al alloy Bridgman crystals. The dislocation density increased upon increasing the Al concentration to more than 0.5at%. The frequency of formation of sub-boundaries and dislocation clusters also increased when the crystals contained more than 1at%Al. In the case of 5at%Al crystals, dislocation clusters which were ringed by a sub-boundary frequently formed together with sub-boundaries. It was deduced that the dislocation sub-structures might arise from the segregation of Al atoms which occurred, at the solid/liquid interface, due to constitutional supercooling.

Y.Imashimizu, J.Watanabe: Journal of the Japan Institute of Metals, 1995, 59[9], 894-901