METHOD FOR FABRICATING A FUNCTIONALLY-GRADED MONOLITHIC SINTERED WORKING COMPONENT FOR MAGNETIC HEAT EXCHANGE AND AN ARTICLE FOR MAGNETIC HEAT EXCHANGE

• US 20130187077A1
• Filed: 08/17/2011
• Published: 07/25/2013
• Est. Priority Date: 08/18/2010
• Status: Active Grant

• Current Assignee: Vacuumschmelze GmbH & Company KG (Vectra Corp.)
• Original Assignee: Vacuumschmelze GmbH & Company KG (Vectra Corp.)
• Inventors: Katter, Matthias, Barcza, Alexander, Zellmann, Volker
• Granted Patent: US 9,978,487 B2
• Time in Patent Office: Days
• US Class Current: 252/62.51C
• CPC Class Codes: B23P 15/26 heat exchangers or the like making heat exchangers by methods covered by other subclasses B21D53/02
• CPC Class Codes: H01F 1/015 Metals or alloys
• CPC Class Codes: H01F 1/017 Compounds
• CPC Class Codes: Y10T 29/4935 Heat exchanger or boiler making
• CPC Class Codes: Y10T 428/24992 Density or compression of components

Abstract

An article for magnetic heat exchange includes a functionally-graded monolithic sintered working component including La_1-aR_a(Fe_1-x-yT_yM_x)₁₃H_zC_b with a NaZn₁₃-type structure. M is one or more of the elements from the group consisting of Si and Al, T is one or more of the elements from the group consisting of Mn, Co, Ni, Ti, V and Cr and R is one or more of the elements from the group consisting of Ce, Nd, Y and Pr. A content of the one or more elements T and R, if present, a C content, if present, and a content of M varies in a working direction of the working component and provides a functionally-graded Curie temperature. The functionally-graded Curie temperature monotonically decreases or monotonically increases in the working direction of the working component.

Claims

1. A method for fabricating a functionally-graded monolithic sintered working component for magnetic heat exchange, comprising:

providing powder comprising elements in amounts suitable to form a La_1-aR_a(Fe_1-x-yT_yM_x)₁₃H_zC_b phase with a NaZn₁₃-type structure, wherein T is one or more of the elements from the group consisting of Mn, Co, Ni, Ti, V and Cr, M is one or more of the elements from the group consisting of Si and Al, and R is one or more of the elements from the group consisting of Ce, Nd, Y and Pr,

forming the powder to provide a green body in which the amount of the one or more elements T and R, if present, the amount of C, if present, and the amount of M varies in a pre-determined direction of the green body,

heat treating the green body at a temperature T and for a time t selected to allow diffusion of one or more of the elements T, R and C, and

forming a working component comprising a functionally-graded Curie temperature that monotonically increases or monotonically decreases in the predetermined direction.

2. The method according to claim 1, wherein

the temperature T and the time t are selected to provide a functionally-graded Curie temperature that decreases or increases with a gradient that lies within ±

10% of a linear function of Curie temperature per unit length over 80% of a length of the working component.

3. The method according to claim 1, wherein

the temperature T is selected to provide a diffusion rate of the elements T and/or C of at least 2×

10<sup>−

11</sup> m²/s.

4. The method according 3claim 1, wherein

the temperature T is selected to provide a diffusion rate of the element C of at least 1×

10<sup>−

10</sup> m²/s.

5. The method according to claim 1, wherein

the temperature T is 900°

C.≦

T≦

1200°

C.

6. The method according to claim 1, wherein

the temperature T is 1050°

C.≦

T≦

1150°

C.

7. The method according to claim 1, wherein

the time t is 1 h≦

t≦

100 h.

8. The method according to claim 1, further comprising providing a plurality of powders comprising differing R, T, M and/or C contents selected to provide differing Curie temperatures when suitably heat treated to form the NaZn₁₃ structure.

9. The method according to claim 8, wherein

layers of the plurality of powders are stacked such that the content of R, T, M and/or C increases or decreases in a direction of the stack.

10. The method according to claim 8, wherein

each of the powders is mixed with a liquid and optionally with a binder and/or a dispersant to form a plurality of slurries or paste.

11. The method according to claim 8, wherein

the viscosity of the slurry or paste is 200 mPas and 100,000 mPas.

12. The method according to claim 11, wherein

the slurries or pastes are applied to a surface layer by layer to form a stack such that the content of R, T, M and/or C increases or decreases in a direction of the stack.

13. The method according to claim 12, wherein

the layers have a thickness of 10 μ

m to 60 μ

m.

14. The method according to claim 10, wherein

before sintering, the liquid and binder and/or dispersant, if present, are removed at a temperature of 500°

C. or below.

15. The method according to claim 8, wherein varying proportions of the powders are mixed with one another before being arranged in a former such that the content of R, T, M and/or C of the powder in the former increases or decreases over a length of the former.

16. The method according to claim 8, wherein varying proportions of the powders are introduced in the former such that the content of R, T, M and/or C increases or decreases in the insertion direction.

17. The method according to claim 1, wherein

the powder is formed to the green body by applying pressure.

18. The method according to claim 1, wherein

the green body is sintered at a temperature of 900°

C. or greater to produce a density of 90% or more of a theoretical density.

19. The method according to claim 1, wherein

M is Si and the amount of Si is selected according to Si_m=3.85−

0.0573×

Co_m−

0.045×

Mn_m²+0.2965×

Mn_m, wherein Si_m is the metallic weight fraction of silicon, Mn_m is the metallic weight fraction of manganese and Co_m is the metallic weight fraction of cobalt.

20. The method according to claim 1, wherein

M is Si and the amount of Si is selected according to Si_m=3.85−

0.045×

Mn_m²+0.2965×

Mn_m+(0.198−

0.066×

Mn_m)×

Ce(MM)_m, wherein Si_m is the metallic weight fraction of silicon, Mn_m is the metallic weight fraction of manganese and Ce(MM)_m is the metallic weight fraction of cerium misch metal.

21. The method according to claim 1, further comprising hydrogenating the working component after the heat treating.

22. The method according to claim 21, wherein

the working component is hygrogenated to produce a working component comprising a hydrogen content z of at least 90% of the hydrogen saturation value, z_sat, of the NaZn₁₃-structure.

23. The method according to claim 21, wherein the working component is hydrogenated to produce a hydrogen content z of 1.4≦

z≦

3 in the La_1-aR_a(Fe_1-x-yT_ySi_x)₁₃H_z phase.

24. The method according to claim 21, wherein

the hydrogenating comprises heat treating under a H₂ partial pressure of 0.5 to 2 bar.

25. The method according to claim 21, wherein

the H₂ partial pressure is increased during hydrogenating.

26. The method according to claim 21, wherein

the hydrogenating comprises heat treating at a temperature in the range 0°

C. to 100°

C.

27. The method according to claim 26, wherein

the hydrogenating comprises heat treating at a temperature in the range 15°

C. to 35°

C.

28. The method according to claim 21, wherein

the hydrogenating comprises a dwell at a temperature T_hyd, wherein 300°

C.≦

T_hyd≦

700°

C.

29. The method according to claim 28, wherein

the hydrogenating comprises a dwell at a temperature T_hyd, wherein 300°

C.≦

T_hyd≦

700°

C. followed by cooling in a hydrogen atmosphere to a temperature of less than 100°

C.

30. The method according to claim 21, wherein the hydrogenating comprises:

heating the working component from a temperature of less than 50°

C. to at least 300°

C. in an inert atmosphere,

introducing hydrogen gas only when a temperature of at least 300°

C. is reached, maintaining the working component in a hydrogen containing atmosphere at a

temperature in the range 300°

C. to 700°

C. for a selected duration of time, and cooling the working component to a temperature of less than 50°

C.

31. The method of claim 30, wherein

the working component is cooled to a temperature of less than 50°

C. in a hydrogen-containing atmosphere.

32. Method according to claim 21, wherein

hydrogen gas is introduced only when a temperature of 400°

C. to 600°

C. is reached.

33. The method according to claim 21, wherein

after hydrogenating, the working component comprises at least 0.18 wt % hydrogen.

34. The method according to claim 30, wherein

the working component is heat treated in a temperature gradient and a varying amount of hydrogen is introduced into, or removed, from the working component in dependence of the temperature gradient to produce a functionally-graded Curie temperature that increases or decreases monotonically in the pre-determined direction.

35. An article for magnetic heat exchange, comprising a functionally-graded monolithic sintered working component comprising La_1-aR_a(Fe_1-x-yT_yM_x)₁₃H_zC_b with a NaZn₁₃-type structure, wherein M is is one or more of the elements from the group consisting of Si and Al, T is one or more of the elements from the group consisting of Mn, Co, Ni, Ti, V and Cr and R is one or more of the elements from the group consisting of Ce, Nd, Y and Pr, a content of the one or more elements T and R, if present, a C content, if present, and a content of M varying in a working direction of the working component and providing a functionally-graded Curie temperature, the functionally-graded Curie temperature monotonically decreasing or monotonically increasing in the working direction of the working component.

36. The article according to claim 35, wherein

the functionally-graded Curie temperature increases or decreases with a gradient that lies within ±

10% of a linear function of Curie temperature per unit length determined over 100% of the length of the working component.

37. The article according to claim 36, wherein

the functionally-graded Curie temperature decreases or increases within ±

5% of the linear function or within ±

2% of the linear function.

38. The article according to claim 35, wherein

the functionally-graded Curie temperature decreases or increases over 90% of a length of the working component within ±

10% of the linear function.

39. The article according to claim 35, wherein

the working component comprises an average Curie temperature gradient of 5°

C./mm to 0.5°

C./mm over 80% of the length of the working component.

40. The article according to claim 35, wherein

the working component has a density d in a defined portion of 5 vol % to 10 vol % of the total volume of the working component, wherein d lies within a range of ±

5% or ±

2% of an average total density d_av of the working component.

41. The article according to claim 35, wherein

the working component comprises an increasing M content or a decreasing M content for increasing amounts of one or more of the elements T and R.

42. The article according to claim 35, wherein

the amount of M lies within the range 0.05≦

x≦

0.2.

43. The article according to claim 35, wherein

the monolithic working component comprises Co and/or Mn and additionally silicon and the silicon content, Si_act, lying within ±

5% of Si_m, wherein Si_m=3.85−

0.0573×

Co_m−

0.045×

Mn_m²+0.2965×

Mn_m, wherein Si_m is the metallic weight fraction of silicon, Mn_m is the metallic weight fraction of manganese, Co_m is the metallic weight fraction of cobalt.

44. The article according to claim 43, wherein

Si_act lies within ±

2% of Si_m.

45. The article according to claim 35, wherein

0≦

a≦

0.5 and 0.003≦

y≦

0.2 or 0.05≦

a≦

0.5 and 0≦

y≦

0.2 or 0.05≦

a≦

0.5 and 0.003≦

y≦

0.2.

46. The article according to claim 35, wherein

0≦

b≦

1.5 or 0.05≦

b≦

0.5.

47. The article according to on claim 35, wherein

0≦

z≦

3 or 1.4<

z≦

3.

48. The article according to claim 35, wherein

T is one or more of the group consisting of Co and Ni and wherein z=0.

49. The article according to claim 35, wherein

T is one or more of the group consisting of Mn, Ti, V and Cr and R is one or more of the group consisting of Ce, Nd and Pr and wherein 1.4<

z≦

3.