The growth of α Plates During Annealing in a β′Cu-Zn Alloy

Morphology and growth of α plates which appear during annealing in the temperature range from 150 to 300°C were investigated by using repeated electropolishing technique. The results obtained are summarized as follows. All the α plates were triangles with a tip angle of 70 degree, but the opposite side of the tip, or growing front, showed various shapes depending upon individual α plate. The α plates became thicker near the tip, and the cross section of that portion had almost the same thickness. On the other hand, the α plates became thinner near the opposite side of the tip, and the thickness decreased with approaching to the both edges. The values of width and length of α plates were almost the same after the same annealing time below 225°C. On the other hand, above 250°C, the growth rate of the longitudinal direction (length) was faster than that of the transverse direction (width). The growth rate of the horizontal direction of α plates was obviously slower than those of the longitudinal and transverse directions at any annealing temperature. The activation energy for growth of α plates was about 120–156 kJ/mol. This value is of the same order as those for diffusion of copper and zink atoms in Cu-Zn alloys.