Claims
- 1. A sintered magnet comprising R, T and B wherein R is at least one element of rare earth elements inclusive of yttrium and T is iron or iron and cobalt, and containing 2 to 15% by volume of closed voids.
- 2. The sintered magnet of claim 1 which contains 3 to 15% by volume of closed voids.
- 3. The sintered magnet of claim 1 which has a density of up to 7.2 g/cm.sup.3.
- 4. The sintered magnet of claim 1 wherein the closed voids each have an average projection cross-sectional area of 1,000 to 30,000 .mu.m.sup.2.
- 5. The sintered magnet of claim 1 wherein the fraction of open voids is up to 2% by volume.
- 6. The sintered magnet of claim 1 which consists essentially of 30 to 45% by weight of R, 0.5 to 3.5% by weight of B and the balance of T.
- 7. The sintered magnet of claim 1 which has not been shaped after sintering and which has a parallel portion, wherein the maximum length divided by the average thickness of said parallel portion is at least 10, and a thickness deviation is up to 1.5%, the thickness deviation being the difference between the maximum and the minimum of thickness of said parallel portion divided by the maximum length of said parallel portion.
- 8. The sintered magnet of claim 1 which has not been shaped after sintering and which has a cylindrical portion, wherein the average outer diameter divided by the average wall thickness of said cylindrical portion is at least 10, and an outer diameter deviation is up to 1.5%, the outer diameter deviation being the difference between the maximum and the minimum of outer diameter of said cylindrical portion divided by the average outer diameter of said cylindrical portion.
- 9. The sintered magnet of claim 1 which has not been shaped after sintering and which has a cylindrical portion, wherein the average outer diameter divided by the average wall thickness of said cylindrical portion is at least 10, and an inner diameter deviation is up to 1.5%, the inner diameter deviation being the difference between the maximum and the minimum of inner diameter of said cylindrical portion divided by the average inner diameter of said cylindrical portion.
- 10. The sintered magnet of claim 1 which contains 0.5 to 10% by weight of an R oxide.
- 11. The sintered magnet of claim 1, prepared by a process comprising the steps of compacting a mixture of a magnet powder having crystal grains consisting essentially of R.sub.2 T.sub.14 B and an R oxide powder to form a compact having a density of at least 5.5 g/cm.sup.3 and sintering the compact so as to induce a density change of at least 0.2 g/cm.sup.3.
- 12. The sintered magnet of claim 11, wherein said magnet powder has a mean particle size of 30 to 350 .parallel.m.
- 13. The sintered magnet of claim 1 prepared by a method comprising the steps of compacting a mixture of a powder of a primary phase-forming master alloy having crystal grains consisting essentially of R.sub.2 T.sub.14 B, a powder of a grain boundary phase-forming master alloy consisting essentially of 70 to 97% by weight of R and the balance of iron and/or cobalt, and a powder of an R oxide to form a compact and sintering the compact.
- 14. The sintered magnet of claim 13, wherein said primary phase-forming master alloy powder has a mean particle size of 30 to 350 .mu.m.
- 15. The sintered magnet of claim 13, wherein said boundary phase-forming master alloy is left on a screen having an opening of at least 38 .mu.m, but passes a screen having an opening of up to 500 .mu.m.
- 16. The sintered magnet of claim 11, wherein said R oxide powder is present in said mixture in a proportion of 0.5 to 10% by weight and has a mean particle size of 0.5 to 20 .mu.m.
- 17. The sintered magnet of claim 13, wherein said R oxide powder is present in said mixture in a proportion of 0.5 to 10% by weight and has a mean particle size of 0.5 to 20 .mu.m.
- 18. A sintered magnet comprising R, T and B, wherein R is at least one element of the rare earth elements inclusive of yttrium, and T is iron or iron and cobalt,
- wherein said magnet is made by compacting a mixture of a powder of a primary phase-forming master alloy and a powder of a grain boundary phase-forming master alloy with a compacting pressure of at least 6 t/cm.sup.2, and sintering the compact to form said magnet containing 2-15% by volume of closed voids,
- wherein grains of said primary phase-forming master alloy have a mean particle size of at least 20 microns, and grains of said grain boundary phase-forming master alloy have particles sizes from 38 to 500 microns.
Priority Claims (4)
Number |
Date |
Country |
Kind |
5-353916 |
Dec 1993 |
JPX |
|
5-353917 |
Dec 1993 |
JPX |
|
5-353675 |
Dec 1993 |
JPX |
|
6-87861 |
Mar 1994 |
JPX |
|
Parent Case Info
This is a Division of application Ser. No. 08/364,756 filed on Dec. 27, 1994, now U.S. Pat. No. 5,641,363.
US Referenced Citations (4)
Number |
Name |
Date |
Kind |
4921531 |
Nagle et al. |
May 1990 |
|
4952252 |
Ghandehari |
Aug 1990 |
|
5057148 |
Micheli et al. |
Oct 1991 |
|
5536334 |
Kabayashi et al. |
Jul 1996 |
|
Non-Patent Literature Citations (1)
Entry |
Akira Fukuno, et al, "Near-Shaped ND-FE-B Sintered Magnet", Abstracts of the Japan Institute of Metals, 1 page, Oct. 8, 1994 (with English translation). |
Divisions (1)
|
Number |
Date |
Country |
Parent |
364756 |
Dec 1994 |
|