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

Abstract

The magnetic property of Nd23Dy10Fe64TM2B1 alloy was investigated by the convergent heat treatment at 350 to 450A degrees C with the heating/cooling rate of 10A degrees 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.