Development of Formation Technique and Chracterization of Nanocrystal Material form Ultra Fine Powder and MA Process

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The purpose of this research was to make nanocrystal materials using ultra fine powder or powder produced by mechanical alloying process and to develop functional material using the characteristics of nanocrystal. The main results obtained were as follows :1. The particle size of the ultra fine powder produced by plasma-powder process was decreased with the decrease in chamber pressure and powder feeding rate.2. It was shown to be possible to produce bulk materials with 50nm in grain size by sintering Ultra fine powder under the condition of low temperature and high pressure. Such bulk materials exhibited the hardness of 4 to 6 times higher than the regular materials with ordinary grain size. However, when sintering is carried out for the powder of a puremetal element, grain growth occurred even at low temperature.3. When the mixed ultra fine powder of Cu and AIN was sintered, Ultra fine grained material with the stationally grain size of 0.4mum was produced. It was made clear that the pinning effect of the second phase which does not dissolve into matrix works well to stabilize the ultra fine grained structure.4. When the powders of the binary alloys in Al-Ni-Ti system were mechanically alloyed, phases of amorphous, super saturated solid solution or intermetallic compounds were produced depending on the chemical compositions.5. Mechanically alloyed powder was well sintered when the amount of exothermic heat was large. The grain size of Sintered material was extremely small and usually about 0.1mum.6. By applying the grain refinement by MA, nitrides of Sm_2Fe_<17> and NdMo_2Fe_<10> were produced. The grain size of these materials were observed to be about 50nm and it was considered that the single magnetic domain structure was obtained. The coercivity of the above material was measured to be higher that those obtained by regular casting or repid solidification process.