Structure, phase composition and magnetic properties of Fe–Si–C system due to mechanical activation of Fe–Si alloy in organic liquids

Fineness, structure, phase composition, and magnetic properties of the powders produced by mechanical milling of Fe80Si20 in liquid hydrocarbon environment (heptane, heptane with oleic acid additive) in planetary ball mill have been studied. Under milling the alloys are saturated with the products of organic liquid decomposition – C, O, H, and then metastable amorphous and carbide phases form. The particle size decreases down to 0.1–0.2 μm. Isochronous (775 K, 1 h) annealing leads to the formation of the Fe8Si2C iron silicon carbide, as well as Fe3Si and C – for milling in heptane, and Fe3C and SiO2 – for milling with oleic acid additive. The magnetic properties of the powders depend both on the milling time and milling environment, and on the annealing temperature. An increase in the coercivity from 13 up to 226 Oe correlates with the amount of the synthesized Fe8Si2C. It is ferromagnetic (Tc = 788 K) and temperature-resistant up to 870 K.