R-T-B based sintered magnet
An R-T-B based sintered magnet having R 2 T 14 B crystal grains and a grain boundary formed by two or more adjacent R 2 T 14 B crystal grains. An R—Co—Cu—N concentrated part whose concentrations of R, Co, Cu and N are respectively higher than those in the R 2 T 14 B crystal grains may be in the grain boundary. An R—O—C concentrated part or an R—O—C—N concentrated part may be further provided in the grain boundary.
1. An R-T-B based sintered magnet comprising:
a plurality of R 2 T 14 B crystal grains;
at least one grain boundary formed by two or more adjacent R 2 T 14 B crystal grains; and
an R—Co—Cu—N concentrated part in the at least one grain boundary,
wherein concentrations of R, Co, Cu and N in the R—Co—Cu—N concentrated part are respectively higher than concentrations of R, Co, Cu and N in the plurality of R 2 T 14 B crystal grains, and
a ratio of atom number composition of N to a total atom number composition in the R—Co—Cu—N concentrated part is in the range of 10% to 15%.
2. The R-T-B based sintered magnet as set forth in claim 1 , further comprising an R—O—C concentrated part in the at least one grain boundary,
wherein concentrations of R, O and C in the R—O—C concentrated part are respectively higher than concentrations of R, O and C in the plurality of R 2 T 14 B crystal grains.
3. The R-T-B based sintered magnet as set forth in claim 2 , wherein the R—O—C concentrated part is formed within a boundary defined by the R—Co—Cu—N concentrated part in the grain boundary.
4. The R-T-B based sintered magnet as set forth in claim 1 , further comprising an R—O—C—N concentrated part in the at least one grain boundary,
wherein concentrations of R, O, C and N in the R—O—C—N concentrated part are respectively higher than concentrations of R, O, C and N in the plurality of R 2 T 14 B crystal grains.
5. The R-T-B based sintered magnet as set forth in claim 4 , wherein the R—O—C—N concentrated part is formed within a boundary defined by the R—Co—Cu—N concentrated part in the grain boundary.
6. The R-T-B based sintered magnet as set forth in claim 1 , wherein the at least one grain boundary is formed by two adjacent R 2 T 14 B crystal grains.
7. The R-T-B based sintered magnet as set forth in claim 1 , wherein the at least one grain boundary is formed by three adjacent R 2 T 14 B crystal grains.
8. The R-T-B based sintered magnet as set forth in claim 1 , wherein the plurality of R 2 T 14 B crystal grains have a tetragonal crystal structure.
9. The R-T-B based sintered magnet as set forth in claim 1 , wherein the plurality of R 2 T 14 B crystal grains have an average crystal diameter in the range of 1 μm to 30 μm.
10. The R-T-B based sintered magnet as set forth in claim 1 , wherein a ratio of an atom number composition of R to the total atom number composition in the R—Co—Cu—N concentrated part is in the range of 60% to 65%.
11. The R-T-B based sintered magnet as set forth in claim 1 , wherein a ratio of atom number composition of Co to the total atom number composition in the R—Co—Cu—N concentrated part is in the range of 10% to 14%.
12. The R-T-B based sintered magnet as set forth in claim 1 , wherein a ratio of atom number composition of Cu to the total atom number composition in the R—Co—Cu—N concentrated part is in the range of 4% to 7%.
13. The R-T-B based sintered magnet as set forth in claim 2 , wherein the R—O—C concentrated part has a cubic crystal structure.
14. The R-T-B based sintered magnet as set forth in claim 2 , wherein a ratio of an atom number of O to an atom number of R in the R—O—C concentrated part is in the range of less than 1.
15. The R-T-B based sintered magnet as set forth in claim 14 , wherein the ratio of the atom number of O to the atom number of R in the R—O—C concentrated part is in the range of 0.5 to 0.7.
16. The R-T-B based sintered magnet as set forth in claim 1 , wherein the content of R in the plurality of R 2 T 14 B crystal grains is in the range of 25 mass % to 35 mass %.
17. The R-T-B based sintered magnet as set forth in claim 1 , wherein the content of B in the plurality of R 2 T 14 B crystal grains is in the range of 0.5 mass % to 1.5 mass %.
18. The R-T-B based sintered magnet as set forth in claim 1 , wherein T comprises Fe and Co and the content of Co in the plurality of R 2 T 14 B crystal grains is in the range of 0.3 mass % to 4.0 mass %.
19. An electric motor having a rotor comprising a permanent magnet, wherein the permanent magnet includes the R-T-B based sintered magnet as set forth in claim 1 .