Process for production of R-Fe-B-based rare earth sintered magnet, and steam control member
View Patent ↗A sintered R—Fe—B based rare-earth magnet body 1 including, as a main phase, crystal grains of an R 2 Fe 14 B type compound that includes a light rare-earth element RL, which is Nd and/or Pr, as a major rare-earth element R is provided. A bulk body 2 including a heavy rare-earth element RH, which is at least one of Dy, Ho and Tb is also provided. The sintered magnet body 1 and the bulk body 2 are arranged in a processing chamber 4 with a vapor control member 3 interposed between the sintered magnet body 1 and the bulk body 2 . And the inside of the processing chamber 4 is heated to a temperature of 700° C. to 1000° C., thereby diffusing the heavy rare-earth element RH inside the sintered magnet body 1 while supplying the heavy rare-earth element RH from the bulk body 2 to the surface of the sintered magnet body 1 via the vapor control member 3.
1. A method for producing a sintered R—Fe—B based rare-earth magnet, the method comprising the steps of:
providing a sintered R—Fe—B based rare-earth magnet body including, as a main phase, crystal grains of an R 2 Fe 14 B type compound that includes a light rare-earth element RL, which is at least one of Nd and Pr, as a major rare-earth element R;
providing a bulk body including a heavy rare-earth element RH, which is at least one element selected from the group consisting of Dy, Ho and Tb;
arranging the sintered R—Fe—B based rare-earth magnet body and the bulk body in a processing chamber with a vapor control member interposed between the sintered R—Fe—B based rare-earth magnet body and the bulk body; and
heating the inside of the processing chamber to a temperature of 700° C. to 1000° C., thereby diffusing the heavy rare-earth element RH into the sintered R—Fe—B based rare-earth magnet body while supplying the heavy rare-earth element RH from the bulk body to the surface of the sintered R—Fe—B based rare-earth magnet body via the vapor control member,
wherein the vapor control member includes:
an upper surface and a lower surface;
a plurality of openings, which communicate between the upper and lower surfaces; and
a wall portion, which defines the openings, and
wherein the wall portion has a thickness of 0.5 mm or less,
each said opening of the vapor control member has a depth of 1 mm to 10 mm,
D/A is equal to or smaller than 8 mm −1 , where each said opening of the vapor control member has an area of A [mm 2 ] and a depth of D [mm], and
in the step of heating, a gap between the sintered R—Fe—B based rare-earth magnet body and the vapor control member is set to be within a range of 0 mm to 10 mm, a gap between the vapor control member and the bulk body is set to be within a range of 0 mm to 10 mm, and a gap between the sintered R—Fe—B based rare-earth magnet body and the bulk body is set to be 10 mm or less.
2. The method of claim 1 , comprising the step of supporting the sintered R—Fe—B based rare-earth magnet body on the upper surface of the vapor control member and supplying the heavy rare-earth element RH from the bulk body, which is arranged to face the lower surface of the vapor control member, to the surface of sintered R—Fe—B based rare-earth magnet body.
3. The method of claim 1 , wherein a portion of the vapor control member that contacts with the sintered R—Fe—B based rare-earth magnet body is coated with an anti-sticking film.
4. The method of claim 1 , wherein the vapor control member is made of a ceramic material.
5. The method of claim 1 , wherein the vapor control member has a flat end facet on the upper and lower surfaces.
6. The method of claim 1 , wherein each of the openings of the vapor control member is defined as a cuboid space, of which four faces are surrounded with the wall portion.
7. The method of claim 1 , wherein the openings of the vapor control member are arranged so as to form a honeycomb structure.
8. The method of claim 1 , wherein each of the gaps has a fixed value during the heating step.