Mechanochemical Synthesis of a Precursor for the Formation of a Magnetostrictive Functional Material Galfenol under Sintering Conditions

The products of mechanochemical synthesis and subsequent sintering of the Fe-20 wt % Ga system are studied by X-ray diffraction, electron diffraction, Mossbauer spectroscopy, and transmission, scanning and optical microscopy. After mechanical activation for 2 min in planetary ball mill AGO-2, about 70% of Fe is preserved and the FeGa3 intermetallic compound appears. Sintering of the resulting Fe/FeGa3 mechanocomposite takes place with the participation of a liquid phase. In the compacted material, the crystallite size of iron halves and the level of microstraines decreases fivefold. A structure with grain sizes of 3-8 mu m forms and the microhardness is 360 HV. A sharp change in the phase composition of the mechanocomposite is observed after mechanical activation for 60 min: the FeGa3 phase disappears, an Fe(Ga) solid solution with a high gallium content appears, and about 50% of Fe is retained. After mechanical activation for 120 min, a Fe3Ga/Fe(Ga)/Fe mechanocomposite forms (grain sizes are 4-6 mu m, microhardness is similar to 780 HY), sintering of which proceeds according to a solid-phase mechanism. The sintered materials are ferromagnetic. For the materials sintered from precursors after activation for 2 and 120 min, the coercive force is 35 and 77 Oe, respectively, the saturation magnetization is M sa t = 162 and 131 A m(2) kg(-1), and the residual magnetization is M-res 2.8 and 2.1 A m(2) kg(-1).

Automated summary

Mechanochemical synthesis and subsequent sintering of the Fe-20 wt % Ga system result in the formation of Fe-based composites with varying phase compositions and microstructures. The materials exhibit good ferromagnetic properties, with different coercive forces, saturation magnetization, and residual magnetization depending on the activation and sintering conditions.