R-T-B based sintered magnet
An R-T-B based sintered magnet has a high coercivity even if the carbon content becomes high accompanying the micronization of the finely pulverized particles of the raw material. The R-T-B based sintered magnet includes an R-T-B based compound as main phase grains, wherein, the R-T-B based sintered magnet contains 0.1 mass % to 0.3 mass % of C, and an R—Ga—C concentrated part exists in the grain boundary formed between or among two or more adjacent main phase grains, and the concentrations of R, Ga and C in the R—Ga—C concentrated part are higher than those in the main phase grains respectively.
1. An R-T-B based sintered magnet comprising:
an R-T-B based compound as main phase grains,
Ga in an amount of 0.42 mass % or more and 1.5 mass % or less, and
C in an amount in a range of from 0.21 mass % to 0.3 mass %,
wherein
R represents at least one rare earth element,
T represents one or more elements comprising Fe or a combination of Fe and Co,
an average grain size of the main phase grains is in a range of from 1.5 μm to 2.8 μm,
an R—Ga—C concentrated part exists in a grain boundary formed between or among two or more adjacent main phase grains,
concentrations of R, Ga, and C in the R—Ga—C concentrated part are higher than those in the main phase grains respectively,
a content of R in the R-T-B based sintered magnet is 31.87 mass % or more and 32.45 mass % or less,
a content of B in the R-T-B based sintered magnet is 0.75 mass % or more and 0.86 mass % or less, and
a content of a heavy rare earth element contained as R in the R-T-B based sintered magnet is 1.0 mass % or less.
2. The R-T-B based sintered magnet of claim 1 , wherein the R—Ga—C concentrated part further comprises Cu, and a concentration of Cu in the R—Ga—C concentrated part is higher than that in the main phase grains.
3. The R-T-B based sintered magnet of claim 2 , wherein the R—Ga—C concentrated part further comprises Co, and a concentration of Co in the R—Ga—C concentrated part is higher than that in the main phase grains.
4. The R-T-B based sintered magnet of claim 1 , wherein the R—Ga—C concentrated part further comprises Co, and a concentration of Co in the R—Ga—C concentrated part is higher than that in the main phase grains.
5. The R-T-B based sintered magnet of claim 1 , wherein:
a content of Co in the R-T-B based sintered magnet is 0.3 mass % or more and 4.0 mass % or less.
6. A rotating machine comprising the R-T-B based sintered magnet of claim 1 .
7. The R-T-B based sintered magnet of claim 1 , further comprising Zr in an amount of 0.2 mass % or more and 1.5 mass % or less.
8. The R-T-B based sintered magnet of claim 1 , wherein the R—Ga—C concentrated part is a single, continuous area within the grain boundary.
9. The R-T-B based sintered magnet of claim 8 , wherein the grain boundary contains R—Ga—C concentrated parts.
10. The R-T-B based sintered magnet of claim 1 , wherein the R—Ga—C concentrated part is formed in the grain boundary by the formation of a compound of R and Ga with C during manufacturing.
11. The R-T-B based sintered magnet of claim 1 , wherein the R—Ga—C concentrated part is formed in the grain boundary by performing a heat treatment step in which a temperature is maintained in a range of from 500 to 700° C. for 30 minutes to 3 hours before raising the temperature to a sintering temperature.
12. The R-T-B based sintered magnet of claim 1 , wherein the content of B in the R-T-B based sintered magnet is 0.75 mass % or more and 0.81 mass % or less.
13. An R-T-B based sintered magnet comprising:
an R-T-B based compound as main phase grains,
Ga in an amount of 0.42 mass % or more and 1.5 mass % or less, and
C in an amount in a range of from 0.21 mass % to 0.3 mass %,
wherein
R represents at least one rare earth element,
T represents one or more elements comprising Fe or a combination of Fe and Co,
an average grain size of the main phase grains is in a range of from 1.5 μm to 2.8 μm,
an R—Ga—C concentrated part exists in a grain boundary formed between or among two or more adjacent main phase grains,
concentrations of R, Ga, and C in the R—Ga—C concentrated part are higher than those in the main phase grains respectively,
a content of B in the R-T-B based sintered magnet is 0.75 mass % or more and 0.81 mass % or less, and
a content of a heavy rare earth element contained as R in the R-T-B based sintered magnet is 1.0 mass % or less.