2023-05-09 22:00:00
All “soft” ferromagnets, crystalline or not, are essential constituents of almost all the electrical or electronic devices of our modern civilization. Their main role is to amplify and/or channel the magnetic flux produced by a current or a magnet. The current market for these materials can be divided into four main families:
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(a) electrical steels (mainly Fe-3% Si alloys);
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(b) les alliances fer-nickel et fer-cobalt ;
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(c) soft ferrites;
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(d) amorphous and nanocrystalline metal alloys.
The economic interest of these materials reflects their annual worldwide production. For example, family (a) can be split into two: grain-oriented Fe-Si sheets (GO) with a worldwide production of 2 Mt/year mainly used for the manufacture of distribution transformers, and non-oriented sheets ( NO) with a production of 11 Mt/year used mainly in the production of electrical machines. The production of materials of families (b) and (c) is of the order of a few tens of kt/year and 1 to 2 Mt/year with significant use in electronics. A reasonable estimate of the world tonnage of materials of family (d), which interests us here, was 20 kt/year in 1997 and would be around 300 to 600 kt/year in 2023 for nanocrystalline materials with a forecast of growth of 10% per year, i.e. around 1 Mt/year in 2033, and around 1 Mt/year for amorphous minerals with a growth forecast of 6%, i.e. a little less than 2 Mt/year in 2033.
These materials (d) can be obtained by various processes, we will focus here on those prepared in the form of ribbons by rapid solidification of a liquid. The product will be amorphous, that is to say that the atoms constituting it do not present any long-range order. For certain particular atomic compositions, it will be possible by controlled crystallization of the amorphous alloy to obtain two-phase materials comprising a nanocrystalline phase included in a matrix which remains amorphous. Amorphous and nanocrystalline materials exhibit low magnetic anisotropy which can be adapted to applications targeted by post-quenching heat treatments. Their magnetic properties are remarkable: a low coercive field, high permeability (impedance or initial), low electromagnetic losses and ease of controlling the properties by heat treatments. Depending on their compositions, these alloys have saturation magnetizations between 0.5 and 1.7 T with magnetostriction values that can be close to zero up to 35 × 10−6.
This wide range of magnetic properties means that these materials can, for certain applications, compete with the three other categories of soft ferromagnets (a, b, c). They can in fact be used in a wide spectrum of frequencies which goes from direct current up to approximately 1 MHz. In the field of low frequencies, mention may be made of: medium-power distribution transformers and inductors; for higher frequencies, magnetic components for power electronics.
Many other applications exist: magnetic shielding, various sensors, etc. If we look at it from an economic point of view, we can say that amorphous and nanocrystalline materials are more expensive than their steel or ferrite competitors, but that they become interesting if the superiority of their properties makes it possible to reduce the volume of the component, or from the moment when the losses produced during use become an essential criterion. The upward trend in the price of energy is therefore a very favorable factor for the development of these materials.
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