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

本研究的目的是利用超细粉末或机械合金化制备纳米晶材料，开发利用纳米晶特性的功能材料。主要研究结果如下：1.等离子体粉末法制备的超细粉末的粒度随着腔体压力和送粉率的降低而减小。结果表明，在低温高压条件下，通过超细粉末的烧结可以制备出粒度为50 nm的块体材料。这种块体材料的硬度比普通晶粒度的普通材料高4~6倍。然而，当对纯金属元素的粉末进行烧结时，即使在较低的温度下也会发生晶粒长大。将铜和氮化铝混合的超细粉末进行烧结，可得到稳定晶粒度为0.4微米的超细晶材料。结果表明，第二相的钉扎作用对稳定超细晶组织起到了很好的作用，第二相不溶于基体。对Al-Ni-Ti系二元合金粉末进行机械合金化时，会产生非晶相、过饱和固溶体相或金属间化合物相。当放热量较大时，机械合金化粉末的烧结效果较好。烧结物的颗粒非常细小，通常在0.1微米左右。采用机械合金化细化氮化物的方法，制备了Sm_2Fe_(17)和NdMo_2Fe_(10)氮化物。观察到这些材料的晶粒度约为50 nm，并认为得到了单一的磁畴结构。测得上述材料的矫直力高于常规铸造和快速凝固的结果。

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.