磁性蓄冷材を使用した小型冷凍機 遠心噴霧法により作製したＥｒ系磁性蓄冷材の機械的性質

Abstract

Various magnetic regenerator materials, such as Er3Ni, Er3Co, ErNi and ErNi2, are fabricated in the form of a spherical particle by centrifugal atomization. 4K level refrigeration has been achieved by a GM refrigerator using these materials. However, the magnetic regenerator materials are considered brittle, as they are intermetallic compounds. It is important to evaluate the mechanical properties of these materials to confirm their reliability as a regenerator material. In this paper, experimental results of compression and vibration tests for magnetic regenerator materials are described. The technical point of this study is to use spherical particles in a diameter range of 0.18-0.25mm as test samples. The compressive stress of 20MPa was applied to these spherical particles and no fractured spheres were found in the scope of observation. A few spheres were fractured by the compressive stress of at least 50MPa. The morphology of fractured spheres shows brittle fracture. Moreover, no fractured spheres were observed after the vibration test, in which the maximum acceleration was 294m/s2 and the number of vibrations was 1×106, as far as there was no room to stir spherical particles in a test vessel. In practice, the reliability of Er3Ni spheres has been confirmed by a long-run test of 7, 700h in a usual GM refrigerator.