Cu-Al系2元合金における過共析組成の恒温変態について

抄録

In the previous report, the authors tried to obtain the T/T/T-diagrams for two kinds of Cu-Al binary alloys containing 11.44 wt% and 12.18 wt%Al respectively. And it was found that some complex phenomena occurred with the decomposition of the β phase at the temperature below the eutectoid temperature. In consideration of the results of this experiment, the following processes may be deemed reasonable. When T_h>T_c, β→α or γ₂+E and when T_h<T_c, β→β₁+α→E+α. T_h and T_c stand for the temperature of holding and the critical temperature of β→β₁, respectively. It has been shown that the transformation β→β₁ preferentially proceeds at the temperature below T_c, and some characteristic structures, the so-called rosettes or granular precipitates and sheaths enveloping α have appeared with the formation of β₁. Now, to confirm these phenomena again, the authors have carried out some experiments for obtaining the T/T/T-diagrams for the specimens of 12.49 wt%, near the ideal Cu₃Al composition, and of 12.96 wt%Al content. From the present experimental results, it was found that the transformation β→β₁ predominantly proceeds at the temperature below T_c causes the alteration of Al concentration, and then the eutectoidal decomposition occurs directly from the β phase of the alloy containing 12.49 wt%Al. Some discussions about the mechanism of the transformation β→β₁ in Cu-Al binary alloys are appended.