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

1989年，设计并建造了磁场冲击压实装置。由于该装置配备了新研制的光纤测速系统，测量精度高，重复性好。对于重量为10g的弹丸，使用60g火药时，最大射速可达1.9公里/S，比设计能力提高了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。由于25kJ的高能电容器组，磁场可能高到足以饱和普通材料中的磁通量。使用Kantodenka有限公司提供的超细铁粉作为起始粉。由于粉末呈针状，长径比为10：30，堆积密度较低，仅为32%，导致冲击温度升高过大。经超声波分散和沉积后，密度提高到41%，采用冲击压实的方法可以得到密度为71%的压坯。使用复合冲击器的多级冲击压缩技术大大抑制了冲击温度，并提供了密度为92%的良好压坯。今后有必要进一步提高粉末在磁场作用下的压制密度。这项技术有望改善磁性能。压坯的显微组织由纳米晶颗粒组成，没有晶粒生长。因此，我们有可能获得纳米晶金属材料。然而，为了改善磁性能，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.