Sinter magnet made from rare earth-iron-boron alloy powder for magnet
A rare-earth-iron-boron based alloy powder, in which a heavy rare-earth element such as Dy is present at a higher concentration in a main phase than in a grain boundary phase and which can be sintered easily, and a method of making such an alloy powder are provided. A rare-earth-iron-boron based magnet alloy according to the present invention includes, as a main phase, a plurality of R 2 Fe 14 B type crystals (where R is at least one element selected from the group consisting of the rare-earth elements and yttrium) in which rare-earth-rich phases are dispersed. The main phase includes Dy and/or Tb at a higher concentration than a grain boundary phase does.
1 . A rare-earth-iron-boron based magnet alloy comprising, as a main phase, a plurality of R 2 Fe 14 B type crystals (where R is at least One element selected from the group consisting of the rare-earth elements and yttrium) in which rare-earth-rich phases are dispersed,
wherein the main phase includes Dy and/or Tb at a higher concentration than a grain boundary phase does.
2 . The rare-earth-iron-boron based magnet alloy of claim 1 , wherein the alloy includes 2.5 mass % to 15 mass % of Dy and/or Tb.
3 . The rare-earth-iron-boron based magnet alloy of claim 1 , wherein the ratio of Dy and/or Tb to the main phase is at least 1.03 times as high as the ratio of Dy and/or Pb to the overall alloy.
4 . The rare-earth-iron-boron based magnet alloy of claim 1 , wherein the alloy includes at most 5 vol % of α-Fe phase.
5 . The rare-earth-iron-boron based magnet alloy of claim 1 , wherein the alloy includes 27 mass % to 35 mass % of the rare-earth element.
6 . A powder of the rare-earth-iron-boron based magnet alloy of claim 1 .
7 . A sintered magnet made from the rare-earth-iron-boron based magnet alloy powder of claim 6 .
8 . A method of making a rare-earth-iron-boron based magnet alloy, the method comprising the steps of: preparing a melt of a rare-earth-iron-boron based alloy; and making a solidified alloy by quenching the melt,
wherein the step of making the solidified alloy includes the step of forming a solidified alloy layer, including, as a main phase, a plurality of R 2 Fe 14 B-type crystals (where R is at least one element selected from the group consisting of the rare-earth elements and yttrium) in which rare-earth-rich phases are dispersed, by quenching the melt through contact with a cooling member, the main phase including Dy end/or Tb at a higher concentration than a grain boundary phase does.
9 . The method of claim 8 , wherein the alloy includes 2.5 mass % to 15 mass % of Dy and/or Tb.
10 . The method of claim 8 , wherein the ratio of Dy and/or Tb to the main phase is at least 1.03 times as high as the ratio of Dy and/or Tb to the overall alloy.
11 . The method of claim 8 , wherein the step of forming the solidified alloy layer includes forming a first texture layer in contact with the cooling member and then further feeding the melt onto the first texture layer to grow the R 2 Fe 14 B-type crystals on the first texture layer, thereby forming a second texture layer thereon.
12 . The method of claim 11 , wherein in forming the first texture layer, the melt is quenched at a rate of 10° C./s to 1,000° C./s and at a supercooling temperature of 100° C. to 300° C., and
wherein in forming the second texture layer, the melt is quenched at a rate of 1° C./s to 500° C./s.
13 . The method of claim 8 , wherein the R 2 Fe 14 B-type crystals have an average minor-axis size of at least 20 μm and an average major-axis size of at least 100 μm.
14 . The method of claim 8 wherein the rare-earth-rich phases are dispersed at an average interval of 10 μm or less in the R 2 Fe 14 B-type crystals.
15 . The method of claim 8 , wherein the solidified alloy includes at most 5 vol % of α-Fe phase.
16 . The method of claim 8 , wherein the rare-earth element included in the solidified alloy has a concentration of 27 mass % to 35 mass %.
17 . The method of claim 8 , comprising the step of forming the solidified alloy layer by a centrifugal casting process.
18 . A method of making a magnet powder for a sintered magnet, the method comprising the steps of:
preparing the rare-earth-iron-boron based magnet alloy by the method of claim 8; and
pulverizing the alloy.
19 . A method for producing a sintered magnet, the method comprising the steps of:
preparing the rare-earth-iron-boron based magnet alloy powder of claim 6;
compressing the powder under an aligning magnetic field to make a compact; and
sintering the compact.