MAGNET

Abstract

Magnets and systems, methods, and techniques for manufacturing magnets are provided. In some embodiments, methods of manufacturing magnets comprise providing a rare earth magnetic body, cold spray depositing a layer of dysprosium or terbium onto the magnetic body to form a magnet, and heat-treating the magnet. Some embodiments provide a magnet comprising a magnetic body and a layer of dysprosium or terbium. In some embodiments, the magnetic body contains grains of rare earth magnet alloy, and the layer of dysprosium or terbium is deposited onto a surface of the magnetic body by a cold spray process.

Claims

1. A method of manufacturing a magnet, the method comprising: providing a magnetic body containing grains of a rare earth alloy; cold spray depositing a layer of dysprosium onto a surface of the magnetic body to form a magnet; and heat-treating the magnet.

2. The method of claim 1, wherein heat-treating the magnet comprises a grain boundary diffusion process.

3. The method of claim 1, wherein heat-treating the magnet comprises: heating the magnet to a first elevated temperature; cooling the magnet to second temperature; and quenching the magnet to room temperature.

4. The method of claim 3, wherein the first elevated temperature is at least 900 C.

5. The method of claim 3, wherein the second temperature is at least 500 C.

6. The method of claim 3, wherein the magnet is held at the first elevated temperature for at least 6 hours.

7. The method of claim 3, wherein the magnet is held at the second temperature for at least 0.5 hours.

8. The method of claim 1, wherein the rare earth alloy is a neodymium alloy.

9. The method of claim 8, wherein the neodymium alloy is Nd.sub.2Fe.sub.14B.

10. A magnet comprising a magnetic body and a layer of dysprosium; wherein the magnetic body contains grains of a rare earth magnet alloy, and the layer of dysprosium is deposited onto a surface of the magnetic body by a cold spray process.

11. The magnet of claim 10, wherein the magnetic body is sintered.

12. The magnet of claim 10, wherein the rare earth magnet alloy is a neodymium alloy.

13. The magnet of claim in 12, wherein the neodymium alloy is Nd.sub.2Fe.sub.14B.

14. The magnet of claim 10, wherein an amount of dysprosium is diffused within the grains.

15. The magnet of claim 14, wherein the grains contain an amount of diffused dysprosium of between 0.5 to 15 percent by weight.

16. The magnet of claim 14, wherein the dysprosium is diffused along the boundaries of the grains to form a shell layer.

17. The magnet of claim 16, wherein the magnetic body comprises grains of Nd.sub.2Fe.sub.14B with a shell layer comprising Dy.sub.2Fe.sub.14B or (Dy,Nd).sub.2Fe.sub.14B.

18. The magnet of claim 16, wherein the shell layer has a thickness of about 0.5 m.

19. The magnet of claim 10, wherein the deposition thickness of the layer of dysprosium is between 1 to 5 m.

20. A method of manufacturing a magnet, the method comprising: providing a magnetic body containing grains of a rare earth alloy; cold spray depositing a layer of terbium onto a surface of the magnetic body to form a magnet; and heat-treating the magnet.

21. The method of claim 20, wherein heat-treating the magnet comprises a grain boundary diffusion process.

22. The method of claim 20, wherein heat-treating the magnet comprises: heating the magnet to a first elevated temperature; cooling the magnet to second temperature; and quenching the magnet to room temperature.

23. The method of claim 22, wherein the first elevated temperature is at least 900 C.

24. The method of claim 22, wherein the second temperature is at least 500 C.

25. The method of claim 22, wherein the magnet is held at the first elevated temperature for at least 6 hours.

26. The method of claim 22, wherein the magnet is held at the second temperature for at least 0.5 hours.

27. The method of claim 20, wherein the rare earth alloy is a neodymium alloy.

28. The method of claim 27, wherein the neodymium alloy is Nd.sub.2Fe.sub.14B.

29. A magnet comprising a magnetic body and a layer of terbium; wherein the magnetic body contains grains of a rare earth magnet alloy, and the layer of terbium is deposited onto a surface of the magnetic body by a cold spray process.

30. The magnet of claim 29, wherein the magnetic body is sintered.

31. The magnet of claim 29, wherein the rare earth magnet alloy is a neodymium alloy.

32. The magnet of claim 31, wherein the neodymium alloy is Nd.sub.2Fe.sub.14B.

33. The magnet of claim 29, wherein an amount of terbium is diffused within the grains.

34. The magnet of claim 33, wherein the grains contain an amount of diffused terbium of between 0.5 to 15 percent by weight.

35. The magnet of claim 33, wherein the terbium is diffused along the boundaries of the grains to form a shell layer.

36. The magnet of claim 35, wherein the magnetic body comprises grains of Nd.sub.2Fe.sub.14B with a shell layer containing terbium.

37. The magnet of claim 35, wherein the shell layer has a thickness of about 0.5 m.

38. The magnet of claim 29, wherein the deposition thickness of the layer of terbium is between 1 to 5 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order that the present invention may be more readily understood, an embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0020] FIG. 1 shows a cross-sectional schematic representation of a magnet according to some embodiments; and

[0021] FIG. 2 is a flowchart showing the manufacturing process of the magnet according to some embodiments.

DETAILED DESCRIPTION OF THE INVENTION

[0022] The magnet 1 of FIG. 1 comprises a magnetic body 2 and a layer of dysprosium metal 3 deposited on a surface of the magnetic body 2.

[0023] The magnetic body 2 comprises sintered grains 4 of a rare earth alloy. The grains 4 are shown as discrete granules with a boundary. Specifically, the bulk substance within the grains 4 comprises a Nd2Fe14B alloy. The grains 4 adjacent the deposited surface each have a shell layer 5 around their boundary. The shell layer 5 comprises diffused dysprosium which has substituted into the crystal lattice structure of the rare earth alloy. Although dysprosium can diffuse into the bulk of the crystal structure within the grains 4, careful control of the heat treatment conditions allow for diffusion to occur more readily at the grain boundaries. Specifically the shell layer 5 comprises a Dy2Fe14B or (Dy,Nd)2Fe14B alloy where the dysprosium has substituted into the neodymium alloy. The shell layer 5 of dysprosium containing alloy formed around each grain 4 has an approximate thickness of 0.5 m.

[0024] The layer of dysprosium metal 3 is applied directly onto the magnetic body 2 using a cold spray technique. The layer 3 is shown to be uniform and to completely cover the top surface of the magnetic body 2. However, any surface of the magnetic body 2 may have a layer of dysprosium deposited onto it, and the layer 3 can be applied in a uniform or non-uniform manner The thickness of the layer is shown schematically in the figures. A minimum thickness is desired to promote diffusion of dysprosium within or around the grains 4. However, a diminishing return of improved coercivity and magnetic properties is observed past a layer thickness of 5 m.

[0025] A method of manufacturing the magnet 1 will now be described with reference to FIG. 2. A magnetic body 2 containing grains of a Nd2Fe14B alloy 4 is provided. A surface of the magnetic body 2 is chosen to be coated in dysprosium. Dysprosium metal particles 6 are targeted, discharged and deposited onto the chosen surface. The conditions used for cold spray of other metal powders, such as copper and iron can be applied to the cold spraying of dysprosium metal particles. The deposited dysprosium metal rapidly forms a layer 3 on the targeted surface of the magnetic body 2.

[0026] Following the deposition of dysprosium, the magnet 1 is heat treated. During the heat treatment, the shell layer forms around the grains of the magnetic body 2. The heat treatment comprises a grain boundary diffusion process, such that the heat treatment causes dysprosium in the coating layer 3 to diffuse along the boundaries of grains 4 in the magnetic body 2 to form a shell layer 5 containing a dysprosium containing alloy 5. The heat treatment follows the general method of heating the coated magnet 1 at a constant rate to an elevated first temperature and holding the magnet 1 at that elevated temperature for a time period of at least 6 hours. The first elevated temperature should be close to 1000 C., ideally 900 C. This temperature is hot enough to initiate and propagate the diffusion of dysprosium whilst avoiding sintering or melting of the magnetic grains 4.

[0027] The magnet 1 is then cooled at a controlled rate to a second elevated temperature which is lower than the first. The magnet 1 is held at this second elevated temperature for less time, around 30 minutes, before it is quenched to room temperature using a controlled cooling rate. The quenched magnet 1 exhibits improved magnetic properties, for example an increased coercivity.

[0028] The grains 4 comprise a Nd2Fe14B alloy. The grains can also comprise other magnetic rare earth alloys, such as those containing samarium, praseodymium or cerium, particularly SmCo5 and Sm(Co, Fe, Cu, Zr)7. The diffusion of the dysprosium layer 3 along the boundaries of the alloy grains 4 readily occurs for at least these rare earth alloys.

[0029] The grains 4 can be wholly coated in the shell layer 5, as shown in the figures. Alternatively, agglomerated grains 4 can be coated with a shell layer 5, such that the shell layer 5 only covers the exposed boundaries of the grains 4.

[0030] Further research has shown that rare earth magnetic metal terbium can also be used in a cold spray deposition process to create a rare earth magnet with improved coercivity.