Method of making Nd-Fe-B sintered magnets with Dy or Tb
A method of making a permanent magnet is described. In one embodiment, the method includes providing a first alloy powder having a desired composition, the alloy powder containing neodymium, iron, and boron; coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy so that the first alloy powder has a surface concentration of dysprosium, terbium, or both in excess of a bulk concentration of dysprosium, terbium, or both; and forming the permanent magnet from the coated alloy powder using a powder metallurgy process, the permanent magnet having a non-uniform distribution of dysprosium, terbium, or both therein. Permanent magnets are also described.
1. A method of making a permanent magnet comprising:
providing a first alloy powder having a desired composition, the first alloy powder containing neodymium, iron, and boron;
coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy so that the first alloy powder has a surface concentration of dysprosium or terbium, in excess of a bulk concentration of dysprosium or terbium;
screening the first alloy powder before coating the first alloy powder; and
forming the permanent magnet from the coated alloy powder using a powder metallurgy process, the permanent magnet having a non-uniform distribution of dysprosium, terbium, or both therein.
2. The method of claim 1 wherein providing the first alloy powder comprises:
melting and strip casting an alloy containing neodymium, iron, and boron to make strips;
hydrogen decrepitating the strips;
pulverizing the decrepitated strips to make a starting powder;
mixing the starting powder with a second alloy powder to form the first alloy powder.
3. The method of claim 1 wherein forming the magnet from the coated alloy powder using a powder metallurgy process comprises:
pressing the coated alloy powder;
isostatic pressing the pressed coated alloy powder; and
sintering and aging the isostatic pressed powder to form the permanent magnet.
4. The method of claim 3 further comprising machining the permanent magnet.
5. The method of claim 1 wherein the surface concentration of the coated alloy powder is in a range of about 5 to about 80 wt % dysprosium or terbium.
6. The method of claim 1 wherein the average concentration of a magnet is in a range of about 0.3 to about 6.0 wt % dysprosium or terbium.
7. The method of claim 1 wherein the coating on the first alloy powder has a thickness of less than about 100 micrometers.
8. The method of claim 1 wherein coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy comprises mechanical milling the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy.
9. The method of claim 1 wherein coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy comprises depositing dysprosium, dysprosium alloy, terbium, or terbium alloy using a physical vapor deposition process.
10. The method of claim 9 wherein the physical vapor deposition process is a spark erosion physical vapor deposition process, or a sputtering physical vapor deposition process.
11. The method of claim 1 wherein coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy comprises coating the alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy mixed with a carrier.
12. The method of claim 11 wherein the first alloy powder is coated using a swirl accelerator.
13. The method of claim 1 further comprising heat treating the permanent magnet to change the non-uniform distribution of dysprosium or terbium.
14. A method of making a permanent magnet comprising:
melting and strip casting an alloy containing neodymium, iron, and boron to make strips;
hydrogen decrepitating the strips;
pulverizing the decrepitated strips to make a starting powder;
mixing the starting powder with a second alloy powder to form a first alloy powder having a desired composition, the first alloy powder containing neodymium, iron, and boron;
coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy so that the first alloy powder has a surface concentration of dysprosium or terbium in excess of a bulk concentration of dysprosium or terbium;
forming the permanent magnet from the coated alloy powder using a powder metallurgy process, the permanent magnet having a non-uniform distribution of dysprosium or terbium therein.
15. The method of claim 14 wherein forming the magnet from the coated alloy powder using a powder metallurgy process comprises:
pressing the coated alloy powder;
isostatic pressing the pressed coated alloy powder;
sintering and aging the isostatic pressed powder to form the permanent magnet; and
machining the permanent magnet.
16. The method of claim 14 wherein coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy comprises mechanical milling the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy.
17. The method of claim 14 wherein coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy comprises depositing dysprosium, dysprosium alloy, terbium, or terbium alloy using a physical vapor deposition process.
18. The method of claim 17 wherein the physical vapor deposition process is a spark erosion physical vapor deposition process, or a sputtering physical vapor deposition process.
19. The method of claim 14 wherein coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy comprises coating the first alloy powder with dysprosium, dysprosium alloy, terbium, or terbium alloy mixed with a carrier using a swirl accelerator.
20. The method of claim 14 further comprising heat treating the permanent magnet to change the non-uniform distribution of dysprosium or terbium.