Ryoji Watanabe and Shigeyasu Kôda
The grain boundary reaction phenomena were microscopically studied on Zn-Cu and Zn-Ag alloys containing 2%Cu and 5%Ag respectively, which were aged at 100°, 125°,200° and 250° after being quenched from the temperature of a uniform solid solution. The results obtained were as follows: (1) The nodules of both alloys are the migrating parts of the grains which were formed from the adjacent grains as a nucleus. (2) The nodule which seems to begin from a point of the boundary (Photo. 1) is often a united one of the nodules which start from many points of the boundary. (3) The rate of growth of nodules increases with the increase of the aging temperature, as shown in the isothermal curves (Fig. 5,6). However, as the general precipitates grow to a visible size, the growth of the nodules is arrested. (4) The activation energies of the grain boundary reaction calculated from Fig. 7 and 8 are 13,000 cal/mol for Zn-Cu, and 13,200 cal/mol for Zn-Ag.
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