IRON – BASED MAGNETICALLY SOFT COMPOSITE MATERIALS

Abstract

Iron powder - based magnetically soft materials have been developed with interparticle coatings (Fe-Al-Si, Fe-Al-Ti, Fe-Ti-Si) applied by chemical-thermal treatment, i.e., metallization. The choice of the coating composition and technological approach is based on the following considerations:

∎ to retain the essential magnetic properties of iron — specifically magnetic permeability ( _m), coercive force (H_c), and saturation induction (B_s) — while increasing the resistivity (ρ) by applying coatings to the particles;

∎ the coating should be magnetically permeable (transparent) to ensure a closed magnetic circuit in the composite material, thus preventing the reduction of _m and B_s values, which is typical of magnetic dielectrics.

It has been found that in ternary systems (Fe-Al-Si, Fe-Al-Ti, Fe-Ti-Si), component interactions exhibit exothermic effects caused by metallochemical reactions. The initiating elements are Al and Ti. The transport of gaseous reaction products occurs unidirectionally - from the diffusing elements (Al, Si, Ti) toward Fe. This is explained by the relatively low sublimation temperatures of their chlorides (AlCl₃ – 135°C, SiCl₄ – 57°C, TiCl₄ – 136°C, whereas FeCl₂–1026°C). Therefore, metallization is advantageous at temperatures 600…650°C.

The magnetic properties of the resulting composite material Fe-5.4% Al-9.6% Si are as follows: _m = 4920, Hc = 85 A/m, ρ = 1,0 × 10⁻⁶ Ohm.m, Bs ≥ 1,72 Tl (at H = 2500 A/m), ρ ≤ 5,4 W/kg (at B = 1,5 Tl).

It is also possible to use other powdered metals instead of iron powder as the base matrix material. In that case, it would be feasible to produce hybrid materials with resistivity ρ = (0,1…1,0) Ohm.m, i.e., 2…3 orders of magnitude higher than bulk-alloyed steels. Thus, by maintaining the key magnetic properties of the base material at optimal levels, this technology enables the production of magnetic cores and systems in a solid, i.e., monolithically pressed, form.