Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1991-12-12
1994-10-18
Sheehan, John P.
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148120, H01F 102
Patent
active
053564898
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a novel improved process, with a view to the preparation of high performance permanent magnets based on neodymium-iron-boron. More particularly it relates to a process for manufacturing permanent magnets by the technical process called welding.
By "welding" is denoted a mechanical treatment applied to a metallic alloy and intended to cause the refinement of the constituent grains of this alloy. The welding is defined then by its deformation rate. The mechanical treatments capable of inducing welding are essentially forging, hammering, rolling, drawing, vibrocompacting (compacting by vibration) etc.
BACKGROUND OF THE INVENTION
In European Patent EP-A-0,106,948 is described a process for obtaining magnets based on iron-cobalt-boron-rare earths alloy by the technique called powder metallurgy. While indeed the magnets obtained do have interesting magnetic properties, this process, on the other hand, proves to be particularly complicated and dangerous, in fact it requires numerous precautions to be taken, and especially working under a controlled atmosphere. Moreover, the cost of the magnets thus obtained is relatively high. Finally, while indeed the use of cobalt in the base mixture enables the Curie temperature to be increased quite significantly, and therefore the use temperature of these magnets, on the other hand, a reduction in the coercivity and magnetic properties in general are observed.
In the publication by SHIMODA et al. (J. Appl. Phys. 64 (10) 1988), it is proposed to produce permanent magnets based on a praseodymium-iron-boron-copper mixture and this is achieved with a low deformation ratio, especially less than ten. This production process is carried out by hot pressing under an inert atmosphere at approximately 1,000.degree. C. However, this process enables enhanced magnetic properties to be obtained for small magnets only. What i s more, taking into account their production process especially by sheath rolling, resulting indeed in a refinement of the grains (insufficient, however, with a deformation ratio less than ten), with an inhomogeneous microstructure and a magnetic orientation, only praseodymium enables good results to be obtained. It has been shown in fact that by replacing the praseodymium by neodymium, the magnetic properties fall off drastically, making the addition of copper totally pointless. Now praseodymium is much rarer in the earth's surface than neodymium, hence a cost of magnets based on praseodymium distinctly higher (typically in a ratio of 5 to 1 in relation to neodymium) .
There has also been described a hot welding process in European Patent EP-A-0,269,667 making it possible to obtain, under extensive safety conditions, permanent magnets on an industrial scale showing good magnetic performance. These magnets, based on iron-boron and rare earths have a relatively low production cost, taking into account the process used. Nevertheless, it is desirable to improve their magnetic properties. And this is the object of the present invention.
SUMMARY OF THE INVENTION
The present invention relates to an improved process for the preparation of high-performance permanent magnets from a bulk alloy containing a mixture based on iron-boron and neodymium which, for a temperature range, has a region in which the said alloy occurs as two phases, the one a solid and brittle phase and the other a liquid phase, which process consists: copper atoms, said temperature range so as to obtain a deformation rate of at least ten, in such a manner as to refine the constituent grains of the said alloy into particles of a few micrometers; tempering treatment.
In other words, the present invention consists in replacing, in a bulk alloy based on neodymium-iron-boron, some of the iron and/or neodymium atoms by copper atoms and then in subjecting this alloy to a hot welding treatment. While indeed the use of copper was known per se with a view to improving certain magnetic properties, it was clearly shown, on the other hand, that the use of copper in an iron-boron ra
REFERENCES:
patent: 4921551 (1990-05-01), Vernia et al.
patent: 5055142 (1991-10-01), dela Bathie et al.
patent: 5125988 (1992-06-01), Akioka et al.
A Dictionary of Metallurgy, 1958 pp. 98, 386 and 387, A. D. Merriman.
Shimoda et al., "High-energy cast Pr-Fe-B Magnets" J. Appl. Phy. vol. 64, No. 10, Nov. 15, 1988, pp. 5290-5292.
De La Bathie Rene P.
Lelievre Marc
Nozieres Jean P.
Centre National de la Recherche Scientifique and La Pierre Synth
Sheehan John P.
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