METHOD FOR PRODUCING RFeB SYSTEM SINTERED MAGNET AND RFeB SYSTEM SINTERED MAGNET PRODUCED BY THE SAME
A method for producing an RFeB system sintered magnet with the main phase grains having a grain size of 1 μm or less with a considerably equal grain size, including: preparing a shaped body oriented by a magnetic field and sintering the shaped body, wherein the shaped body is prepared using an alloy powder of an RFeB material having a particle size distribution with an average value of 1 μm or less in terms of a circle-equivalent diameter determined from a microscope image, the alloy powder obtained by pulverizing coarse particles having fine crystal grain, each coarse particle having grains of the RFeB material formed inside, the crystal grains having a crystal grain size distribution with an average value of 1 μm or less in terms of the circle-equivalent diameter determined from a microscope image, and 90% by area or more of the crystal grains being separated from each other.
1 . A method for producing an RFeB system sintered magnet including steps of preparing a shaped body oriented by a magnetic field and sintering the shaped body, wherein the shaped body is prepared using an alloy powder of an RFeB material having a particle size distribution with an average value of 1 μm or less in terms of a circle-equivalent diameter determined from a microscope image, the alloy powder obtained by pulverizing coarse particles having fine crystal grain, each coarse particle having crystal grains of the RFeB material formed inside, the crystal grains having a crystal grain size distribution with an average value of 1 μm or less in terms of the circle-equivalent diameter determined from a microscope image, and 90% by area or more of the grains being separated from each other.
2 . The method for producing the RFeB system sintered magnet according to claim 1 , wherein the shaped body is prepared by placing the alloy powder of the RFeB material in a cavity of a mold and orienting the alloy powder of the RFeB material by a magnetic field without applying a mechanical pressure to the alloy powder, and the shaped body is sintered without applying a mechanical pressure to the shaped body.
3 . The method for producing the RFeB system sintered magnet according to claim 1 , wherein the coarse particles having fine crystal grain used for producing the alloy powder of the RFeB material is obtained by treating a coarse powder of a raw material alloy by an HDDR method.
4 . The method for producing the RFeB system sintered magnet according to claim 3 , wherein the raw material alloy is an alloy produced by a melt spinning method.
5 . The method for producing the RFeB system sintered magnet according to claim 1 , wherein the coarse particles having fine grain are pulverized by a hydrogen pulverization method and further pulverized by a jet mill method using helium gas.
6 . The method for producing the RFeB system sintered magnet according to claim 5 , wherein the hydrogen pulverization treatment is performed at a temperature within a range of 100-300° C. for a period of time within a range of 1-10 hours.
7 . The method for producing the RFeB system sintered magnet according to claim 1 , wherein a powder made of a material containing a higher amount of rare earth than the alloy powder of the RFeB material is mixed in the alloy powder of the RFeB material.
8 . An RFeB system sintered magnet, wherein grains of R 2 Fe 14 B forming a main phase have an average size of 1 μm or less and a degree of orientation of 95% or higher.
9 . The RFeB system sintered magnet according to claim 8 , wherein a ratio b/a calculated from a sectional BSE image including an axis of orientation of the RFeB system sintered magnet is equal to or greater than 0.45, where a denotes a length of a longest axis of a crystal grain and b denotes a length of an axis perpendicular to the longest axis.