Developments of Shock-Compaction Method Under Magnetic Field and of High Performance Magnets

1989年设计并制造了一台磁场冲击压实装置。由于该装置配备了新开发的使用光纤的速度测量系统，因此在测量中获得了高精度和高再现性。用60 g火药，10 g弹丸的最大速度为1.9 km/s，比设计值提高25%。另一方面，在低速范围内，有必要改进粉末室以稳定运行。由于25 kJ的高能电容器组，磁场可能高到足以使通常材料中的磁通饱和。有限公司、用作起始粉末。由于粉末是针状的并且具有10至30的高纵横比，我们仅获得32%的低填充密度，这导致冲击温度增加太多。超声分散和沉降将密度提高到41%，这导致通过冲击压实具有71%的密度的压坯。一个多级冲击压缩技术，使用一个复杂的冲击器大大抑制冲击温度，并提供了良好的压实密度为92%。今后有必要进一步提高烧结密度，在磁场作用下进行烧结。该技术有望提高磁性能。压坯的显微组织由纳米晶颗粒组成，没有晶粒长大。因此，纳米金属材料具有前景。然而，为了提高磁性能，需要进一步的实验研究，如表面处理，添加剂的影响，晶界和磁场之间的关系，等等。

In 1989, an apparatus of shock compaction under magnetic fields were designed and constructed. Since the apparatus was furnished with a velocity-measuring system which was newly developed using optical fibres, high precision and high reproducibility were obtained in the measurements. The maximum velocity obtained were 1.9 km/s for a projectile of 10 g in weight by using gun powder of 60 g and were a capacity of 25 % higher than that designed. On the other hand, in the low velocity range, it was necessary to improve the powder chamber for stable operation. Magnetic field was probably high enough to saturate a magnetic flux in usual materials because of a high energy capacitor bank of 25 kJ.Ultrafine iron powder, which was supplied by Kantodenka, Co., Ltd., was used as a starting powder. Since the powder was needle-like and had a high aspect ratio of 10 to 30, we obtained only a low packing density of 32 % which led to increase shock temperature too much. A ultrasonic dispersion and sedimentation improved the density upto 41 % which led to compacts with density of 71 % by shock compaction. A multi-stage shock-compression technique using a complex impactor considerably suppressed shock temperature and provided good compacts with density of 92 %. It is necessary to increase more the pasking density in future by per-forming the powder under magnetic field. This technique was expected to improve magnetic properties.Microstructures of the compacts consisted of nanocrystalline particles without grain growth. We have, therefore, nanocrystalline metallic materials in prospect. In order to improve magnetic properties, however, further experimental investigations, such as surface treatments, effects of additives relations between grain boundaries and magnetic fields, and so on, are required.