Method for the manufacture of a nanocrystalline magnetic core

1. A method for the manufacture of a magnetic core comprising the steps of:

first, winding an amorphous tape of a soft magnetic nanocrystallizable alloy possessing a first coefficient of thermal expansion onto a carrier made of a material possessing a second coefficient of thermal expansion, wherein the second coefficient of thermal expansion is larger than the first coefficient of thermal expansion;

second, subjecting the wound tape and carrier to a first thermal treatment, wherein the first thermal treatment is configured such that it causes tension to be introduced into the tape by thermal expansion of the carrier, although the alloy remains in an amorphous state, and then removing the carrier from the wound tape after cooling of the wound tape and the carrier; and

third, following the cooling a second thermal treatment of the wound tape without the carrier, wherein the second thermal treatment is configured such that the amorphous alloy structure is transformed into a nanocrystalline alloy structure with at least 50% of the alloy structure being formed of fine crystalline particles having an average particle size of 100 nanometers or less.

2. The method of claim 1 , in which the soft magnetic nanocrystallizable alloy is an iron-based alloy whose chemical composition in atomic percentages is Fe≥50%, 0.1%≤Cu≤3%, 0%≤B≤25%, 0%≤Si≤30% and includes at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo with contents of between 0.1% and 30% and wherein the remaining content consists of impurities resulting from its production and the composition fulfills the relationship 5%≤Si+B≤30%.

3. The method of claim 1 , in which the soft magnetic nanocrystallizable alloy is an alloy having a chemical composition with the general formula (Fe 100-a M a ) 100-x-y-z-α Cu x Si y B z M′ α , wherein in atomic percentages M is equal to Co or Ni, M′ is at least one element selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo and a, x, y, z and α each correspond to the equation 0.0%≤a≤0.5%, 0.1%≤x≤3.0%, 0%≤y≤30.0%, 0%≤z≤25.0%, 5.0%≤y+z≤30.0% and 0.1%≤α≤30.0%.

4. The method of claim 1 , in which the soft magnetic nanocrystallizable alloy is an alloy comprising in atomic percentages Fe 100-a-b-c-d-x-y-z , Cu a , Nb b , M c , T d , Si x , B y , Z z and containing up to 1% impurities, wherein M is Mo or Ta, T is one or several of the elements selected from the group consisting of V, Cr, Co and Ni and Z is one or more of the elements selected from the group consisting of C, P and Ge and 0.0%≤a<1.5%, 0.0%≤b<3.0%, 0.2%≤c≤4.0%, 0.0%≤d<5.0%, 12.0%<x<18.0%, 5.0%<y<12.0% and 0.0%≤z<2.0% and 2.0%≤(b+c)≤4.0%.

5. The method of claim 1 , in which the soft magnetic nanocrystallizable alloy is an alloy comprising in atomic percentages Fe a Co b Ni c Cu d M e Si f B g X h and up to 1% impurities, wherein M is at least one of the elements selected from the group consisting of V, Nb, Ta, Ti, Mo, W, Zr, Cr, Mn and Hf and X is at least one element selected from the group consisting of P, Ge and C and 0≤b≤40; 2<c<20; 0.5≤d≤2; 1≤e≤6; 6.5≤f≤18; 5≤g≤14; h<5 and 5≤b+c≤45 and a+b+c+d+e+f=100.

6. The method of claim 1 further comprising: providing the amorphous tape from a molten iron-based alloy using rapid solidification technology.

7. The method according of claim 1 , in which the second coefficient of thermal expansion is 2 to 80 ppm higher than the first coefficient of thermal expansion.

8. The method of claim 7 , in which the second coefficient of thermal expansion is 3 to 50 ppm higher than the first coefficient of thermal expansion.

9. The method of claim 8 , in which the second coefficient of thermal expansion is 3 to 12 ppm higher than the first coefficient of thermal expansion.

10. The method of claim 1 , in which the core has a circular, elliptic or polygonal outline.

11. The method of claim 1 , in which the amorphous tape is subject to tension of more than 25 MPa during the first thermal treatment.

12. The method of claim 11 , in which the amorphous tape is subject to tension of up to 300 MPa during the first thermal treatment.

13. The method of claim 1 , in which the amorphous tape is subject to maximum temperatures of between 300° C. and 460° C. during the first thermal treatment.

14. The method of claim 1 , in which the first thermal treatment lasts between 0.1 hours and 12 hours.

15. The method of claim 1 , in which the amorphous tape is subject to maximum temperatures of between 520° C. and 600° C. during the second thermal treatment.

16. The method of claim 1 , in which the second thermal treatment lasts between 0.5 and 8 hours.

17. The method of claim 1 , in which the first thermal treatment or the second thermal treatment or both thermal treatments is (are) carried out under a protective gas.

18. The method of claim 17 , in which pure hydrogen is used as the protective gas.

19. The method of claim 1 , in which the second thermal treatment is carried out under the influence of an applied external magnetic field.