Magnetic properties of high coercivity Nd₂₃Dy₁₀Fe₆₄TM₂B₁ sintered magnets by a convergent heat treatment

摘要

The magnetic property of Nd₂₃Dy₁₀Fe₆₄TM₂B₁ alloy was investigated by the convergent heat treatment at 350 to 450°C with the heating/cooling rate of 10°C/min in vacuum (10−5 Torr). The convergent heat treatment was introduced by two mechanisms for the microstructure modification. One is the penetration of Nd-rich phases into the Nd₂Fe₁₄B grains, which results in the isolation of Nd₂Fe₁₄B hard magnet phases. The other is the reduction of crack formation, which is often caused by repeated heating/cooling processes. The result of the convergent heat treatment was compared to that of the cyclic heat treatment, which is known to progress through the mechanism involving thermal expansion coefficients differences. Thus, the effect of the crack formation in the Nd₂Fe₁₄B grains to magnetic properties was restrained by the convergent heat treatment. Consequently, the coercivity was enhanced from 32.5 kOe to about 34.1 kOe after eight cycles of the convergent heat treatment with maintaining a remanence of 1.18 T.