Formation of bulk material of metastable phase by solid-state reaction of complex ultra fine powders.

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In the present investigation the sintering of matal ultra fine powders have been studied for two years. This study was characterized by the fact that the ultra fine powders were handled in one continuous equipment from production to sintering. Especially using the inert gas cleaning system obtained by the present grant, the O_2 and moisture content was kept in quite low state. The main results obtained were as follows.1. The inert gas cleaning system, O_2 and H_2O detectors were censer attached to the grove box and this grove box was directly connected with the ultra fine powder producing system.2. The diamer of ultra fine powder was reduced with reducing the chamber pressure and the material powder feeding rate.3. The density of sintered ultra fine powder at the same sintering temperature was higher when sintered under the pressure than that without pressure at the same sintering temperature. The sintering temperature which gives the same sintering density was 200K lower when sintered … More for that under pressure (300MPa) than that without pressure.4. The hardness of sintered ultra fine powder increases with the progress of sintering and decrease with the progress of grain growth. The maximum hardness obtained was 50OHv for Ni and 25OHv for Cu, which were 7 and 4 nines larger than those of casted.5. The hardness of sintered ultra fine powders was proportional to -1/2 power of the grain size and this indicates that the Hall-Petch relation is held.6. The theoretical consideration of the effect of grain size to the sintering rate and grain growth rate indicates that the temperature region where sintering rate is high and grain growth rate is low increases with the decrease in grain size.7. The mixing of different ultra fine powders after production of each powder was tried using ultrasonic equipment. However microscale mixing was not achieved because of the aggregation. To obtain uniform mixing the best method wascon sidered to mix the material in the vapor condition. A new type double plasma touch ultra fine powder production system was designed. Less