R-Fe-B type rare earth sintered magnet and process for production of the same
AssigneeHitachi Metals, Ltd.
InventorsKoshi Yoshimura, Hideyuki Morimoto, Tomoori Odaka
Life of this patent
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Abstract
In an R—Fe—B based rare-earth sintered magnet according to the present invention, at a depth of 20 μm under the surface of its magnet body, crystal grains of an R2Fe14B type compound have an (RL1-xRHx)2Fe14B (where 0.2≦x≦0.75) layer with a thickness of 1 nm to 2 μm in their outer periphery. In this case, the light rare-earth element RL is at least one of Nd and Pr, and the heavy rare-earth element RH is at least one element selected from the group consisting of Dy, Ho and Tb.
Claims14
An R—Fe—B based rare-earth sintered magnet comprising an R—Fe—B based rare-earth sintered magnet body that includes, as a main phase, crystal grains of an R2Fe14B type compound, including a light rare-earth element RL, which is at least one of Nd and Pr, as a major rare-earth element R, and a heavy rare-earth element RH, which is at least one element selected from the group consisting of Dy, Ho and Tb,
- wherein at a depth of 20 μm under the surface of the R—Fe—B based rare-earth sintered magnet body, the crystal grains of the R2Fe14B type compound include an RH diffused layer at an outer periphery of the crystal grains, the RH diffused layer having an average thickness of 2 μm or less and having a composition of (RL1-xRHx)2Fe14B, where 0.2≦x≦0.75,
- wherein at a depth of 500 μm under the surface of the R—Fe—B based rare-earth sintered magnet body, the crystal grains of the R2Fe14B type compound have an RH diffused layer with an average thickness of 0.5 μm or less in their outer periphery,
- wherein the surface of the R—Fe—B based rare-earth sintered magnet body is a machined surface that is not covered with a metal layer of the heavy rare-earth element RH and that is a surface of the R—Fe—B based rare-earth sintered magnet body, from which its surface portion has already been removed after the heavy rare-earth element RH has been introduced into the R—Fe—B based rare-earth sintered magnet body from outside of the R—Fe—B based rare-earth sintered magnet body,
- wherein the R—Fe—B based rare-earth sintered magnet body has a size of 1 mm to 4 mm as measured in a thickness direction,
- wherein a difference ΔHcJ1 in coercivity is 150 kA/m or less between:
- the entire R—Fe—B based rare-earth sintered magnet body;
- and
- a portion of the R—Fe—B based rare-earth sintered magnet body below a distance of 200 μm from the surface of the R—Fe—B based rare-earth sintered magnet body, and
- wherein the magnet has an RH-RL-O compound in at least one grain boundary triple junction, which is located at a depth of 100 μm or less under the surface of the R—Fe—B based rare-earth sintered magnet body.
An R—Fe—B based rare-earth sintered magnet comprising an R—Fe—B based rare-earth sintered magnet body that includes, as a main phase, crystal grains of an R2Fe14B type compound, including a light rare-earth element RL, which is at least one of Nd and Pr, as a major rare-earth element R, and a heavy rare-earth element RH, which is at least one element selected from the group consisting of Dy, Ho and Tb,
- wherein at a depth of 20 μm under the surface of the R—Fe—B based rare-earth sintered magnet body, the crystal grains of the R2Fe14B type compound include an RH diffused layer at an outer periphery of the crystal grains, the RH diffused layer having an average thickness of 2 μm or less and having a composition of (RL1-xRHx)2Fe14B, where 0.2≦x≦0.75,
- wherein at a depth of 500 μm under the surface of the R—Fe—B based rare-earth sintered magnet body, the crystal grains of the R2Fe14B type compound have an RH diffused layer with an average thickness of 0.5 μm or less in their outer periphery,
- wherein the surface of the R—Fe—B based rare-earth sintered magnet body is a machined surface that is not covered with a metal layer of the heavy rare-earth element RH and that is a surface of the R—Fe—B based rare-earth sintered magnet body, from which its surface portion has already been removed after the heavy rare-earth element RH has been introduced into the R—Fe—B based rare-earth sintered magnet body from outside of the R—Fe—B based rare-earth sintered magnet body,
- wherein the R—Fe—B based rare-earth sintered magnet body has a size of more than 4 mm in the thickness direction,
- wherein a surface region of the R—Fe—B based rare-earth sintered magnet body has a thickness of 1 mm as measured from a surface of the R—Fe—B based rare-earth sintered magnet body and includes:
- a first layer portion with a thickness of 500 μm as measured from the surface;
- and
- a second layer portion that is located deeper inside the R—Fe—B based rare-earth sintered magnet body than the first layer portion and that has a thickness of 500 μm,
- wherein a difference ΔHcJ2 in coercivity between the first and second layer portions is 300 kA/m or less, and
- wherein the magnet has an RH-RL-O compound in at least one grain boundary triple junction, which is located at a death of 100 μm or less under the surface of R—Fe—B based rare-earth sintered magnet body.
Dependencies are inferred from the claim text.