Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1982-10-28
1984-09-25
Rutledge, L. Dewayne
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
75125, 75123F, 75123L, 75123K, 75124, C22C 3800
Patent
active
044734000
DESCRIPTION:
BRIEF SUMMARY
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-crystalline 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 over-stressed 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 cobalt 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 15-25 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 6.degree.-7.degree. 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 1/2.degree. or 1.degree. 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 crystllisation 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 percent: of germanium; 0-7 of silicon; 0-2 of nickel; and 75-85, minus the nickel, of iron, given by Ag+Cu+2Zn.notgreaterthan.4; commercial impurities not being excluded.
Preferably the amount of boron is from 12 to 17 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 4-51/2 percent.
The total of aluminium+boron+carbon+germanium+silicon, which must of course be 100-(iron
ickel+silver/copper/zinc), that is from about 11 to 25 perc
REFERENCES:
patent: 4056411 (1977-11-01), Chen
patent: 4236946 (1980-12-01), Aboaf et al.
patent: 4298409 (1981-11-01), DeCristofaro et al.
National Research Development Corporation
Rutledge L. Dewayne
Yee Debbie
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