Dislocation Formation in Copper-Aluminum Dilute Alloy Crystals during Czochralski Growth Process

Single crystals of copper-aluminum dilute alloys containing 0.05, 0.1, 0.2, 0.5, 1, 2, and 5 at%Al were grown by pulling up from the melt with the [111] orientation at a pulling rate of 1.7×10−5 m/s and a crystal rotation rate of 1 rad/s in a stream of purified argon gas. The density and distribution of dislocations in the pulled crystals were investigated by an etching technique, and the effect of aluminum atoms on the dislocation formation in the copper-aluminum dilute alloy crystals during pulling was examined. (1) A small addition of aluminum suppresses the formation of slip dislocations and the increase of dislocation density from the center to the periphery which occurred frequently in the pulled crystals of copper. Moreover, the mean dislocation density takes a minimum value about 5×107 m−2 at 0.1 at%Al, which is more than one order of magnitude less than that in the copper crystals. (2) On the other hand, the subboundaries and the dislocation clusters were sometimes introduced into the crystals containing 0.05∼0.5 at%Al, which are similar to those found in the copper-aluminum dilute alloy crystals grown by the Bridgman method in the previous work. (3) The dislocation density increases with an increase in aluminum concentration more than 0.5 at%Al. The frequency for the formation of subboundaries and dislocation clusters also increase when the crystals contain more than 1 at%Al. In the 5 at%Al alloy crystals, the dislocation clusters surrounded with a ringed subboundary are frequently formed together with subboundaries. It is inferred that the dislocation substructures might arise from the segregation of aluminum atoms occurred at the labilized solid-liquid interface due to constitutional supercooling.