Dislocation formation during czochralski growth of copper-gold dilute alloy crystals

Single crystals of Cu-0.01, 0.03, 0.05, 0.1 and 0.2 at%Au alloys were grown in the [111] direction under a given condition by the Czochralski method. The distribution and the density of edge dislocations formed in those crystals were examined by etching the (111) cross sections perpendicular to the growth axis. The results are discussed by referring to the dislocation formations in the copper and copper-aluminum dilute alloy crystals investigated in the previous work. (1) In the Cu-0.01 at%Au alloy crystals the slip dislocations revealed as arrays of etch pits along [1 (1) over bar 0] directions are found on some cross sections, while most of the dislocations are randomly distributed. In the Cu-0.03 at%Au alloy crystals, no slip dislocations are observed and moreover the dislocation formation on the periphery of the crystals tends to be suppressed, resulting in the decrease in dislocation density to a minimum value which is about half that of copper crystals. (2) In the crystals containing gold more than 0.05 at%, a substructure of dislocation clusters and subboundaries tends to form and the dislocation density increases with increasing gold concentration. In the Cu-0.2 at%Au alloy crystals, the short subboundaries and dislocation clusters are distributed homogeneously, and the dislocation density becomes very high. (3) The dislocation density of the pulled crystals is reduced by a small addition of gold as well as aluminum, but the lowest density attained by gold addition is higher than that by aluminium addition. The reason is probably that copper-gold alloys give rise to constitutional supercooling during the melt-growth process more easily, so that the dislocation formation due to the segregation of solute atoms would occur at a low concentration compared with copper-aluminum alloys.