US 11,798,717 B2
R-T-B based rare earth permanent magnet
Keiji Takeda, Tokyo (JP); and Shota Miyazaki, Tokyo (JP)
Assigned to TDK CORPORATION, Tokyo (JP)
Appl. No. 16/965,956
Filed by TDK CORPORATION, Tokyo (JP)
PCT Filed Jan. 29, 2019, PCT No. PCT/JP2019/002960
§ 371(c)(1), (2) Date Jul. 29, 2020,
PCT Pub. No. WO2019/151245, PCT Pub. Date Aug. 8, 2019.
Claims priority of application No. 2018-013722 (JP), filed on Jan. 30, 2018; and application No. 2018-013728 (JP), filed on Jan. 30, 2018.
Prior Publication US 2021/0043343 A1, Feb. 11, 2021
Int. Cl. H01F 7/02 (2006.01); H01F 1/057 (2006.01); C22C 38/00 (2006.01)
CPC H01F 1/0577 (2013.01) [C22C 38/005 (2013.01)] 6 Claims
OG exemplary drawing
 
1. An R-T-B based rare earth permanent magnet represented by a compositional formula of (R11-x-ySmxR2y)aTbBcMd, wherein
R1 represents one or more rare earth elements which does not include Sm and R2,
R2 represents one or more rare earth elements selected from Y, Ce, and La,
T represents one or more transition metals essentially including Fe or a combination of Fe and Co,
M represents Ga or a combination of Ga and one or more elements selected from Sn, Bi, and Si,
x and y are on straight lines or in a pentagonal area
surrounded by the straight lines formed by connecting point A (0.010, 0.600), point B (0.010, 0.400), point C (0.050, 0.000), point D (0.150, 0.000), and point E (0.100, 0.600) on (x, y) plane,
a, b, c, and d satisfy relationships of
0.16≤a/b≤0.28,
0.050≤c/b≤0.075, and
0.005≤d/b≤0.028,
the R-T-B based rare earth permanent magnet includes grain boundary phases and a main phase comprising a compound having an R2T14B based tetragonal structure,
an average grain size D50 of main phase crystal grains of the main phase satisfies a relationship of D50≤4.00 μm,
a grain size distribution satisfies a relationship of (D90−D10)/D50≤1.60, in which D10, D50, and D90 respectively represent an area circle equivalent diameter at 10%, 50%, and 90% in a cumulative distribution of a cross sectional area of the main phase crystal grains in an cross section of the R-T-B based rare earth permanent magnet, and
a grain boundary phase coverage is 70.0% or more.