GB2095289A - Magnetic metallic glass alloy - Google Patents

Abstract

An alloy of composition (by mole) around Fe80B15Si5 with additions of up to 4 mole % Ag or Cu or up to 2 mol % Zn or mixtures thereof when rapidly cooled solidifies to a non-crystalline glass structure, which is ductile and magnetically 'soft', i.e. offering a reasonable saturation magnetisation yet with low losses. Exemplary glassy alloy: Fe79.5B15Si5Cu0 &cirf& 5 The range of compositions, in mole percent, lies within <IMAGE> and any one of Ag, Cu, Zn such that Ag+Cu+2Zn NOTGREATER 4.i

Description

SPECIFICATION Magnetic metallic glass alloy This invention relates to a metallic glass alloy with magnetic properties.

Certain metallic alloys, when cooled sufficiently rapidly solidify with a glass structure. In this specification, "glass" refers to the amorphous non-crystailine pseudo-liquid atomic structure characteristic of glasses, and carries no implication as to chemical constitution or translucency. A metallic magnet solidified in the form of metallic glass has important advantages, for certain applications, over a normal crystalline magnet. For example, magnetic metallic glasses may find use in transformers as they are magnetically soft and mechanically ductile and flexible (although if overstressed they may become magnetically harder). After modest shaping, they do not need the costly operation of in situ annealing.

Magnetic metals such as iron, nickel and cobait would therefore be desirable in glass form, but this requires cooling rates beyond present-day possibility. To render these metals in glass form, they must be alloyed, and additions of 1 5-25 atomic % of boron, carbon or silicon to transition metals which are solidified by a spin-quenching technique, involving sufficiently rapid cooling, can fairly reliably result in metallic glass alloys.

There are various tests for confirming whether a magnetic alloy specimen is fully glassy, i.e. is perfectly amorphous, and three tests will be briefly considered: X-ray diffraction, ductility and magnetic coercivity.

The X-ray diffraction pattern of a truly amorphous alloy has a broad peak, about 6o7o 0 wide, corresponding to the mean interatomic spacing. With increasing proportions of crystallinity in a specimen, sharp pips appear on the X-ray pattern (at from about 5% crystallinity), and with greater crystallinity, lines about 1 or 1 0 wide start to appear.

Ductility provides a most convenient qualitative bench test. If a specimen of thin metallic-glass ribbon can be bent back on itself, and straightened out again, it is amorphous, but if the specimen breaks during this test, it is tending to crystallinity.

The coercivity of a specimen extrapolated to zero Hertz, i.e. the d.c. coercivity, is a most sensitive test for crystallinity. A perfectly amorphous magnetic alloy typically has a d.c. coercivity of 30-70 milliOersted, and certainly not more than 0.1 Oe. With a certain proportion of crystallinity, the d.c.

coercivity may be from 0.1 Oe up to 1 Oe, and such specimens may still be usable. Above 1 Oe, the crystallinity is in general too high.

Fe-B-Si glass alloys are known to have good magnetic permeability; while the boron is essential for reliable production of a glass structure, the silicon is found, especially at certain boron concentrations, to reduce the saturation magnetisation by less than the atomic percentage in which it is present; the silicon also increases the crystallisation temperature-that is, improves the thermal stability of the glass.

When considering metallic alloying constituents for improving saturation magnetisation (which is perhaps the most important single property), first principles (atom size, electron structure) suggest that elements such as vanadium, chromium and manganese should be considered. The results are disappointing, and are tabulated hereafter.

According to the present invention, a magnetic metallic glass alloy has the composition, in mole per cent: 0--2 of aluminium; 10-22, minus the aluminium, of boron; 0--8 of carbon; 0--10 of germanium; 0--7 of silicon; 0--2 of nickel; and 75-85, minus the nickel, of iron, characterised by containing any of silver, copper and zinc in an amount given by Ag+Cu+2Zn4; commercial impurities not being exluded.

Preferably the amount of boron is from 12 to 1 7 percent; the aluminium is preferably absent.

Preferably the amount of carbon is from 0 to 4 percent; carbon is more preferably absent.

Preferably the amount of germanium is from 0 to 4 percent, and indeed germanium is more preferably absent.

Preferably the amount of silicon is from 2 to 6 percent, more preferably 45 2 percent.

The total of aluminum+boron+carbon+germanium+silicon, which must of course be 100 (iron/nickel+silver/copper/zinc), that is from about 11 to 25 percent, is preferably from 1 7 to 22 percent.

Preferably, nickel is absent, and the preferred amount of iron is then from 78 to 82 percent.

The silver is preferably absent.

The amount of copper is preferably from 0.2 (more preferably from 0.3, still more preferably from 0.6) to 12 percent (more preferably up to 1 percent, even more preferably up to 0.8 percent). Much above 12 percent the copper tends to precipitate.

The amount of zinc is preferably from 0 to 1 percent. (Zinc may be absent).

The amount Ag+Cu+2Zn, which in the preferred case is the amount Cu+2Zn, is preferably from 0.2 to 3 percent, more preferably from 0.3 to 1 2 percent.

The invention will now be described by way of example.

Example 1 A mixture of iron boride (FeB2), iron, silicon and copper powders, all of commercial purity, was made up giving a batch in which the constituents were in the molar proportions Fe79 sBr5Si5Cu0.5. The batch was melted and allowed to mix thoroughly over a few minutes. The melt was allowed to cool, giving a brittle alloy, which was crushed (for better mixing) and remelted in a crucible with a # mm diameter base ejection nozzle to 50 or 1 OOC degrees above the melting point.

The nozzle was opened and the remelt biown out of the crucible (using argon under 0.2 bar) through the nozzle onto the flat rim of a cold copper wheel of 15 cm diameter spinning at 3000- 6000 e.g. 4000 revolutions per minute. There resulted a ribbon of 25 to 40 m thickness, about 1 + to 3 mm wide, of Fe79.sB15Si5Cu0.5 glass. Its magnetic properties could be marginally improved by annealing for 2 hours at 300C, although this was not in fact done in the Examples.

X-ray diffractometry of the ribbon showed no trace of crystallinity.

The saturation magnetisation per unit mass a was measured for three samples of this material to an accuracy for each sample of about +%. The same was done for three samples of a second batch of alloy, made identically. The reproducibility between samples was + 1%. The average value over all six samples for the saturation magnetisation, measured at 77K and again at 293K, was as follows:- a,7=1 95 emu/g a293=1 73+ emu/g To estimate the Curie temperature Sc, a was assumed to vary with temperature according to the formula, well confirmed experimentally:: aT=aO( 1p(T/Oc)3'2) where p is a constant for any one material; p was taken as 0.43, being the value for Fe80B15Si5, and a0 itself was estimated (from a77 and a293) as 193 emu/g. A notably high value for #c was obtained, consistent with the welcome flatness of the a vs. T curve between 77K and 293K; this value was up to 700K.

The coercivity of the alloy was also measured by the following method. A hysteresis loop of the ribbon was plotted using a pair of identical coils wound on glas tubes (7.5 mm inside diameter, 9 mm outside diameter). The windings were 7 cm long and consisted of 3000 turns for the secondaries, and 486 turns for the primaries, connected in series opposition to compensate for air flux. Single lengths of ribbon were inserted in one of the coils and the output fed to a Tectronic type 536 oscilloscope with type 0 operational amplifier plug-in unit, set up to integrate and amplify the signal. The primaries were energised from an oscillator and amplifier giving a linear variation of current with drive, with repetition frequencies from 10 to 160 Hz. It is well known in amorphous alloys that although HC and the area of the loop are small, the anisotropy energy is fairly large.This has been attributed to stresses which result in domains with a strongly preferred axis not in the plane of the ribbon.

Extrapolating to O Hz, the coercivity Hc was found to be as low as 55 milli0ersted, offering the promise of low losses, without a heavy penalty of reduced saturation magnetisation a.

Example 2-5 The above procedure was repeated making the following glass alloys according to the invention; a77, a293, and Oc (estimated) are also given in units of emu/g or K, starting with the alloy of Example 1 in the same format. The absolute accuracy of #c may be only +50K, but because the errors are probably approximately the same in each estimate of Oc, the ranking of the alloys in order of their Oc is believed to be correct. Coercivity (where measured) was at a maximum field of 5 Oersteds.

Example Alloy a77 a293 Oo 1 Fe795B15Si5Cu0.5 193.5 174.5 700 2 Fe79.6B14.9Si5Zn0.5 194.6 176.6 740 3 Fe79.2B20Cu0.8 196.9 175 700 4 Fe912B13Si5Cu08 199.6 172.5 590 5 Fe80.6B16.5Si2.5Cu0.4 196.1 176.2 695 6 Fe7958175Si25Cu05 197.9 172.7 625 7 Fe79.0B17.5Si2.5Cu1.0 o 197.6 173.7 630 The following comparative glass alloys, not according to the invention, were made and measured for comparison; the results are to the foregoing standard, except for those marked with an asterisk, which are for technical reasons not as certain Alloy a77 a293 Fe8OB158i5 196.5 171.2 625 *Fe70B15Si5V1 180.2 154.9 630 *Fe76B15Si5V4 152.2 130.5 620 Fe79B15Si5Cr1 193.5 167 600 Fe76B15Si5cr4 167.2 140.3 550 *Fe78B15Si5Mn2 173.2 150.4 655 The coercivity (extrapolated to zero frequency) was measured for the following alloys, and had the values given (milliOersteds):- Fe80B15Si5 (comparative)-70 Fe799B15Si9Cu05 (Example 1 )-55 Fe8' B1 8.5Si2.5 (comparative)-43 Fe80.6B16.5Si2.5CU0.4 (Example 5)--41

Claims (24)

Claims

1. A metallic glass alloy having the composition, in mole percent: 0--2 of aluminium; 10-22, minus the aluminium, of boron; 0--8 of carbon; 0--10 of germanium; 0--7 of silicon; 0--2 of nickel; and 75-85, minus the nickel, of iron, characterised by containing any of silver, copper and zinc in an amount given by Ag+Cu+2Zn4; commercial impurities not being excluded.

2. An alloy according to Claim 1, wherein the amount of boron is from 12 to 17 percent.

3. An alloy according to any preceding claim, wherein aluminium is absent.

4. An alloy according to any preceding claim, wherein the amount of carbon is from 0 to 4 percent.

5. An alloy according to Claim 4, wherein carbon is absent.

6. An alloy according to any preceding claim, wherein the amount of germanium is from 0 to 4 percent.

7. An alloy according to Claim 6, wherein germanium is absent.

8. An alloy according to any preceding claim, wherein the amount of silicon is from 2 to 6 percent.

9. An alloy according to Claim 8, wherein the amount of silicon is from 4 to 56 percent.

10. An alloy according to any preceding claim, wherein the total of aluminium, boron, carbon, germanium and silicon is from 17 to 22 percent.

11. An alloy according to any preceding claim, wherein nickel is absent.

12. An alloy according to Claim 11, wherein the amount of iron is from 78 to 82 percent.

13. An alloy according to any preceding claim, wherein silver is absent.

14. An alloy according to any preceding claim, wherein the amount of copper is from 0.2 to 1 percent.

1 5. An alloy according to Claim 14, wherein the amount of copper is at least 0.3 percent.

16. An alloy according to Claim 15, wherein the amount of copper is at least 0.6 percent.

17. An alloy according to Claim 14, 1 5 or 16, wherein the amountof copper is up to 1 percent.

18. An alloy according to Claim 17, wherein the amount of copper is up to 0.8 percent.

19. An alloy according to any preceding claim, wherein the amount of zinc is from 0 to 1 percent.

20. An alloy according to any preceding claim, wherein the total of silver plus copper plus twice the zinc is from 0.2 to 3 percent.

21. An alloy according to Claim 20, wherein the total of silver plus copper plus twice the zinc is from 0.3 to 12 percent.

22. An alloy according to any preceding claim, whose coercivity (extrapolated to zero frequency) is up to 1 Oersted.

23. An alloy according to Claim 22, whose coercivity (extrapolated to zero frequency) is not more than 0.1 Oersted.

24. A metallic glass alloy having substantially one of the following molar compositions: Fe79.5B15Si5CU0.5 Fe79.6B14.9Si5Zn0.5 Fe79.2B2Ocuo.8 Fe812B13Si5Cu08 Fe9o.9Bi6.5Si2.5Cuo Fe79.5B17.5Si2.5Cu0.5 Fe79.OB17.5Si2.5cu1.0