TEM STUDIES OF THE MICROSTRUCTURE OF PRESSURELESS SINTERED COPPER

The microstructure of electrolytic copper powder was investigated duri ng the sintering process by means of transmission electron microscopy and scanning electron microscopy. It is shown that the particle size, which is important for shrinkage, is much smaller than the size of the agglomerates obtained by sieving. The particles are polycrystalline w ith crystallite sizes of about 1 mu m at the beginning of the sinterin g process. Both ex-situ and in-situ sintering were performed. During t he sintering process the crystallite size increases. Recrystallization twinning is observed at temperatures above 400 degrees C. The samples show local dislocation densities of about 10(8) to 10(9) cm(-2). The shrinkage velocities of Coble, Nabarro-Herring, and dislocation creep are calculated and compared to the value experimentally obtained. The shrinkage velocities of all three transport mechanisms discussed here are in the same order of magnitude.