| 简介 |
PROBLEM TO BE SOLVED : To increase the density of a sintered body at a low temp. by controlling its thickness to a specified range, allowing it to contain chill crystals of specified grain size by a specified volume ratio in the vicinity of the cooling face and composing the balance of granular crystals of specified grain size and columnar crystals of specified size. SOLUTION : By a roll rapid cooling method, an alloy thin strip for the raw material of a permanent magnet having 30 to 1000 μm thickness, contg. chill crystals of <=3 μm grain size by 1 to 30% volume ratio in the vicinity of the cooling face, and in which the balance other than the chill crystals is composed of granular crystals of 3 to 50 μm grain size and columnar crystals of 3 to 100 μm minor axis and 20 to 600 μm major axis can be obtd. By pulverizing this thin strip, fine powder having a grain size distribution in which the ones of <=3 μm average grain size are contained by 1 to 30 vol., and the grain size of the balance is 3 to 10 μm can easily be obtd. By using thin fine powder, sintering can be executed at a temp. lower by 20 to 100 deg.C compared to the case in which fine powder having a uniform grain size distribution is used, and its coercive force increases. |
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