Rare earth permanent magnets and their preparation

Patent metadata

Field	Value
Publication number	US-10614952-B2
Application number	US-201715454433-A
Country	US
Kind code	B2
Filing date	Mar 9, 2017
Priority date	May 2, 2011
Publication date	Apr 7, 2020
Grant date	Apr 7, 2020

Abstract

A sintered magnet body (RaT1bMcBd) coated with a powder mixture of an intermetallic compound (R1iM1j, R1xT2yM1z, R1iM1jHk), alloy (M1dM2e) or metal (M1) powder and a rare earth (R2) oxide is diffusion treated. The R2 oxide is partially reduced during the diffusion treatment, so a significant amount of R2 can be introduced near interfaces of primary phase grains within the magnet through the passages in the form of grain boundaries. The coercive force is increased while minimizing a decline of remanence.

First claim

What is claimed is:

1. A method for preparing a rare earth permanent magnet, comprising the steps of:
disposing a powder mixture on a surface of a sintered magnet body having the composition R a T 1 b M c B d wherein R is at least one element selected from rare earth elements inclusive of Y and Sc, T 1 is one or both of Fe and Co, M is at least one element selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, B is boron, “a,” “b,” “c” and “d” indicative of atomic percent are in the range: 12≤a≤20, 0≤c≤10, 4.0≤d≤7.0, the balance of b, and a+b+c+d=100, the powder mixture comprising an alloy powder having the composition R 1 x T 2 y M 1 z wherein R 1 is at least one element selected from rare earth elements inclusive of Y and Sc, T 2 is one or both of Fe and Co, M 1 is at least one element selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, x, y and z indicative of atomic percent are in the range: 5≤x≤85, 20≤z≤95, x+z<100, the balance of y, y>0, and x+y+z=100, containing at least 70% by volume of an intermetallic compound phase, and having an average particle size of up to 500 μm, and 30 to 90% by weight of an R 2 oxide wherein R 2 is at least one element selected from rare earth elements inclusive of Y and Sc, having an average particle size of up to 100 μm, and
heat treating the sintered magnet body having the powder mixture disposed on its surface at a temperature lower than or equal to the sintering temperature of the sintered magnet body in vacuum or in an inert gas, for causing partial reduction of the rare earth oxide in admixture with the intermetallic compound, whereby the elements R 1 , R 2 , M 1 and T 2 in the powder mixture to diffuse to grain boundaries in the interior of the sintered magnet body and/or near grain boundaries within the sintered magnet body primary phase grains.

2. The method of claim 1 wherein the heat treating step includes heat treatment at a temperature from 200° C. to (Ts−10)° C. for 1 minute to 30 hours wherein Ts represents the sintering temperature of the sintered magnet body.

3. The method of claim 1 wherein the disposing step includes dispersing the powder mixture in an organic solvent or water, immersing the sintered magnet body in the resulting slurry, taking up the sintered magnet body, and drying for thereby covering the surface of the sintered magnet body with the powder mixture.

4. The method of claim 1 wherein the atomic percentage of “z” is in the range of 20≤z≤90.

5. A rare earth permanent magnet, which is prepared by disposing a powder mixture on a surface of a sintered magnet body having the composition R a T 1 b M c B d wherein R is at least one element selected from rare earth elements inclusive of Y and Sc, T 1 is one or both of Fe and Co, M is at least one element selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, B is boron, “a,” “b,” “c” and “d” indicative of atomic percent are in the range: 12≤a≤20, 0≤c≤10, 4.0≤d≤7.0, the balance of b, and a+b+c+d=100, the powder mixture comprising an alloy powder having the composition R 1 x T 2 y M 1 z wherein R 1 is at least one element selected from rare earth elements inclusive of Y and Sc, T 2 is one or both of Fe and Co, M 1 is at least one element selected from the group consisting of Al, Si, C, P, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ag, In, Sn, Sb, Hf, Ta, W, Pb, and Bi, x, y and z indicative of atomic percent are in the range: 5≤x≤85, 20≤z≤95, x+z<100, the balance of y, y>0, and x+y+z=100, containing at least 70% by volume of an intermetallic compound phase, and having an average particle size of up to 500 μm, and 30 to 90% by weight of an R 2 oxide wherein R 2 is at least one element selected from rare earth elements inclusive of Y and Sc, having an average particle size of up to 100 μm, and heat treating the sintered magnet body having the powder mixture disposed on its surface at a temperature lower than or equal to the sintering temperature of the sintered magnet body in vacuum or in an inert gas, wherein
the elements R 1 , R 2 , M 1 and T 2 in the powder mixture are diffused to grain boundaries in the interior of the sintered magnet body and/or near grain boundaries within the sintered magnet body primary phase grains so that the coercive force of the rare earth permanent magnet is increased over the original sintered magnet body.

6. The rare earth permanent magnet of claim 5 wherein the atomic percentage of “z” is in the range of 20≤z≤90.

Assignees

• Shinetsu Chemical Co

Inventors

• Nagata Hiroaki
• Nomura Tadao
• Minowa Takehisa

Classifications

• C22C19/07

  based on cobalt · CPC title

• H01F41/0293 Primary

  diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets · CPC title

• B32B15/01

  all layers being exclusively metallic {(making layered metal workpieces by pressure cladding B23K20/22; making coatings with a metallic material characterised by its composition C23C30/00)} · CPC title

• B22F3/12

  Both compacting and sintering (by forging B22F3/17) · CPC title

• C22C38/005

  containing rare earths, i.e. Sc, Y, Lanthanides · CPC title