| In sintered Co-Cu alloys with 30, 40, 50wt % Co the cobalt grain growth in liquid matrix was investigated at the temperature range between 1150℃ and 1300℃. The specimens were prepared by usual powder metallurgy techniques from 1.35㎛ cobalt powder and 4.8㎛ copper power. When sintered and annealed at those temperatures from 30 minutes and 10 hours in the presence of liquid cobalt-copper matrix, spherical cobalt grains were formed. Since the densities of the cobalt grains and the matrix are almost identical, the grains were dispersed uniformly throughout the matrix volume. The increase of the average grain size with annealing time, ｔ, is observed to follow closely the ｔ⅓ law predicted for the diffusion controlled growth mechanism by Lifshitz and Slyozov, Wagner, and Ardell. The growth rate is observed to increase with decreasing matrix fraction, praviding a further evidence for diffusion controlled mechanism. On the other hand the linear intercept distribution agrees closely with the predictions for the reaction controlled mechanism in the Lifshitz, Slyozov, and Wagner (LSW) theory. The results are, however, consistent with Ardell`s prediction that when grains with small inter-grain distance grow by diffusion controlled mechanism the grain size distribution will be almost identical to the reaction controlled mechanism in LSW theory. Therefore, the results agree with Ardell`s predictions for the diffusion controlled growth. The activation energy for the diffusion of cobalt atoms in liquid cobalt-copper matrix was estimated to be 109±5 KJ/㏖. |
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