Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1995-02-15
1998-02-24
Sheehan, John
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148101, 148122, 419 11, 419 14, 419 29, H01F 103
Patent
active
057208280
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to ferromagnetic materials, more especially ferromagnetic materials which contain a rare earth element, iron, nitrogen and carbon, and optionally hydrogen.
The invention relates to both isotropic and anisotropic magnetic materials.
BACKGROUND ART
Ferromagnetic materials and permanent magnets are important materials widely used in electrical and electronic products. The well-established Nd.sub.2 Fe.sub.14 B based magnets have a high saturation magnetization, .mu..sub.o M.sub.s, of 1.6 T, high anisotropy field, .mu..sub.o H.sub.A, of 6.7 T and high energy product, (BH).sub.max., of 360 kJ/m.sup.3 at room temperature. However, the low Curie temperature, T.sub.c, of 310.degree. C. seriously reduces the performance above room temperature.
In recent years, many studies have been conducted on the nitrides and carbides of rare earth iron compounds, and two compounds, Sm.sub.2 Fe.sub.17 N.sub.2.3 and Sm.sub.2 Fe.sub.17 C.sub.2, have been formed with characteristics superior to Nd.sub.2 Fe.sub.14 B. For example, the parameters for Sm.sub.2 Fe.sub.17 N.sub.2.3 are T.sub.c =485.degree. C., .mu..sub.o M.sub.s =1.5 T, .mu..sub.o H.sub.A =15 T, and for Sm.sub.2 Fe.sub.17 C.sub.2 are T.sub.c =407.degree. C., .mu..sub.o M.sub.s =1.4 T and .mu..sub.o H.sub.A =13.9 T. These parameters imply that magnets made from these alloys could have an energy product as high as 470 kJ/m.sup.3, with a superior T.sub.c. However, the .alpha.-Fe precipitated during the nitriding is found to reduce the performance of hard magnets based solely on the nitrides. Furthermore, it is found that above 300.degree. C., a significant quantity of nitrogen is released, reducing T.sub.c.
In contrast, many carbides, despite their relatively smaller T.sub.c and .mu..sub.o H.sub.A, contain little precipitated .alpha.-Fe and have no problems with outgassing.
DISCLOSURE OF THE INVENTION
It is an object of this invention to provide novel intermetallic substances containing iron, a rare earth element, nitrogen and carbon.
It is a particular object of this invention to provide such intermetallic substances in the form of magnetic materials, including isotropic magnetic materials and anisotropic magnetic materials.
It is a further object of this invention to provide a process for producing the intermetallic substances.
It is yet another object of this invention to provide shaped magnetic articles.
In accordance with one aspect of the invention there is provided a magnetic material of formula (I): H.sub..gamma. (I)
R is at least one element selected from Nd, Pr, La, Ce, Tb, Dy, Ho, Er, Eu, Sm, Gd, Pm, Tm, Yb, Lu and Y;
M is at least one element selected from Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Hf, Ta, W, B, Al Si, P, Ga, Ge and As;
preferably less than or equal to 3; said material, in particulate form, having a fully nitrided core substantially free of carbon, and an outer shell comprising Fe.sub.3 C; said material being substantially free of .alpha.-Fe and having a coercivity at 300.degree. K. of at least 1.5 T.
In accordance with another aspect of the invention there is provided a shaped magnetic article formed from the material of formula (I).
In still another aspect of the invention there is provided a magnetic powder comprising the material of formula (I) in particulate form.
In yet another aspect of the invention there is provided a process for producing the material of formula (I), as defined above, which comprises gas absorbing nitrogen and carbon, and hydrogen if present, from a gaseous atmosphere, into a particulate intermetallic compound of formula (II): rhombohedral or hexagonal Crystal structure.
In particular the material of formula (I) is a magnetic material having a high T.sub.c, .mu..sub.o M.sub.s and .mu..sub.o H.sub.A, essentially free of precipitated .alpha.-Fe, and exhibits high stability.
In another aspect of the invention there is provided an anisotropic magnetic material of formula (III): N.sub..alpha.",C.sub..beta."(III)
R is at least one element selected from Nd, Pr, La, Ce, Tb, Dy, Ho, Er,
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Surface Treating Method and Permanent Magnet, vol. 11, No. 46.
Altounian Zaven
Chen Xinhe
Liao Le Xiang
Ryan Dominic Hugh
Strom-Olsen John Olaf
Martinex R&D Inc.
Sheehan John
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