Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Patent
1988-01-13
1991-10-08
Dean, R.
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
148120, H01F 4102
Patent
active
050551426
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a new process for making high-performance permanent magnets by division of the crystals of a magnetic phase in an alloy
In the manufacture of permanent magnets, it was well known to employ metal alloys of iron (Fe)-Boron (B) also including Rare Earths (RE). At the present time, there are essentially two types of preocess for manufacturing such magnets.
In the first process employing powder metallurgy, described in European Patent Applications EP-A-0 101 552, 0 106 948 and 0 126 802, an iron-boron-rare earth alloy is made which is ground in the form of powder, then oriented in a magnetic field which is compressed cold, which is sintered and finally which is subjected to a heat treatment. Although the magnets obtained in this way present excellent properties, this process nonetheless presents noteworthy drawbacks. In fact, the slightest pollution considerably alters the final properties. Now, pollution of the powder by the atmosphere is extremely rapid; this therefore necessitates working under a controlled atmosphere at ambient temperature, which increases manufacturing costs. In addition, it is necessary to employ a grinding phase. Now, the powders used present a high reactivity, particularly with respect to air, which unfortunately involves considerable risks of explosion and of fire.
The second process employs the technique of micro-crystallization. This technique, described in European Patents EP-A-0 125 752 or EP-A-0 133 758, essentially consists in melting an alloy of the type in question, then in subjecting it to a treatment of rapid hardening on roller, in crushing and hot-pressing, or in coating the material obtained in a resin. This technique of very fine jet of liquid at high temperature hardened on cold roller unfortunately leads to isotropic magnets, unless they are subjected to an operation of creep and of recrystallization which is always difficult to carry out in a continuous process. In addition, as a high-temperature fusion is employed with ejection of a very fine liquid, an appropriate apparatus must be used and operation must be carried out in a controlled atmosphere in large-dimensioned enclosures with all the drawbacks that this comprises.
Finally, in these two techniques, one necessarily passes through a phase in the course of which the alloy is considerably divided.
The invention overcomes these drawbacks. It envisages a process of the type in question which is easy to carry out, employs conversions of more economical raw materials, and leads to materials having improved properties.
This process for preparing permanent magnets at ambient temperature from an alloy containing at least one mixture of Iron (Fe), Boron (B) and another element selected from the group that includes rare earth (RE) and yttrium (Y), and for which there is a temperature range inside which said alloy is in two phases: one solid and fragile, and the other liquid. In this process: to attain the said temperature range;
The process is characterized: by welding the magnetic Fe/B/RE solid phase.
In other words, the invention consists firstly in no longer employing an alloy in the form of powder but a bulk alloy comprising two phases, then in heating this bulk alloy, and finally in subjecting it to high mechanical stresses to induce a welding at a temperature allowing the fracture of the magnetic crystals into particles dimensioned on the order of tens of microns and finally, favorably, in cooling this alloy.
In the following specification and claims, the term "controlled atmosphere" is used to designate an atmosphere of which the composition is monitored; in practice, it is question of an atmosphere of noble gases or vacuum, and that in order to avoid reactgions with the Rare Earths;
The term "welding" designates a mechanical treatment applied to the binary-phase (part liquid/part solid) metallic alloy, intended to provoke grain refining of this alloy; treatments of forging, hammering, rolling, extrusion, vibroramming (ramming by vibrations), may be mentioned.
Advantageously, in practice:
the
REFERENCES:
Givord, D. et al., "Magnetic Properties and Crystal Structure of Nd.sub.2 Fe.sub.14 B", Solid State Communications, vol. 50, No. 6, 1984.
Journal of Applied Physics, vol. 59, No. 4, Feb. 15, 1986.
Chavanne Joel
de la Bathie Rene Perrier
Centre National de la Recherche Scientifique
Dean R.
Wyszomierski George
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