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

1989年，设计并研制了磁场冲击压实装置。由于仪器配备了最新研制的光纤测速系统，测量精度高，重现性好。用60g火药，以10g重量的弹体获得的最大速度为1.9 km/s，比设计容量提高25%。另一方面，在低速范围内，为了稳定运行，需要对粉室进行改进。在通常的材料中，磁场可能高到足以使磁通量饱和，因为高能电容器组为25kj。用Kantodenka株式会社提供的超细铁粉作为起始粉。由于粉末呈针状，长径比高达10比30，因此我们只获得了32%的低包装密度，这导致冲击温度过高。超声分散和沉降使密度提高到41%，从而使冲击压实的密度达到71%。采用复合冲击器的多级冲击压缩技术显著地抑制了冲击温度，并提供了密度为92%的良好压实体。今后有必要通过在磁场下进行粉末成形来进一步提高粉末的堆积密度。这项技术有望改善磁性能。压坯的微观结构由纳米晶颗粒组成，没有晶粒生长。因此，我们有纳米晶金属材料的前景。然而，为了提高磁性能，还需要进一步的实验研究，如表面处理、添加剂的影响、晶界与磁场之间的关系等。

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.