Toshiya Shibayanagi1, Yoshihiro Kitazume2 and Shigenori Hori1
1Department of Materials Science and Engineering, Faculty of Engineering, Osaka University, Osaka
The relation between the grain boundary structure and discontinuous precipitation in Cu-2Be alloy has been investigated in connection with Co addition and aging temperature.
The solution treatments of Cu-2Be, Cu-2Be-0.15Co and -0.3Co alloys were performed at 1093 K for 160, 86.4 and 86.4 ks, respectively. The average grain size of Cu-2Be and Cu-2Be-0.15Co alloys was about 70 pm. Cu-2Be-0.3 Co alloy had the average grain size of 40 μm. After aging at 573, 673, 773 and 823 K, the microstructure of specimens were observed with oM, SEM and TEM. The structure of a grain boundaries was characterized with the sigma value in the CLS theory which was determined by analyzing the ECPs (Electron Channeling Patterns) from two grains separated by the grain boundary.
Discontinuous precipitation was not observed at the twin boundaries of these alloys under any aging conditions. The number of grain boundaries without nodules was the least in specimens aged at 673 K. The width of nodules was small at the grain boundary of which the sigma values were smaller than 29 in Cu-2Be alloy aged at 773 K, while there was a weak correlation between the sigma values and the width of nodules in the specimens aged at 673 K. Thus, the influence of the grain boundary characters on the discontinuous precipitation depends on the aging conditions and the driving force for the discontinuous precipitation. The addition of Co retarded the progress of the precipitation without changing the number of grain boundaries without nodules. Meanwhile, the number of grain boundaries without nodules increased with increasing amount of Co.
copper-beryllium alloy, cobalt addition, discontinuous precipitation, gain boundary character, sigma value
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