Bonetti, Ennio and Scipione, Gabriella and Frattini, Romana and Enzo, Stefano and Schiffini, Liliana (1996) Structural and elastic behavior of Fe50Al50 nanocrystalline alloys. Journal of Applied Physics, Vol. 79 (10), p. 7537-7544. eISSN 1089-7550. Article.
Pure iron and aluminum powders were mixed in the equiatomic ratio and mechanically alloyed in a high-energy ball mill for different times. Structure refinement of x-ray powder diffraction data was performed to study the structural transformations induced by mechanical and subsequent thermal annealing treatments. The mechanical alloying (MA) process induces a progressive dissolution of aluminum phase into the bcc iron phase. After 32 h of MA a single-phase Fe(Al) bcc extended solid solution, with lattice parameter a0 = 2.891 Å, average coherent domain size <D> ≈50 Å, and lattice strain 0.5%, was observed. The annealing of the specimens after MA up to 8 h favored the aluminum dissolution in a-iron and the precipitation of the Al5Fe2 phase, whereas a nanostructured B2 FeAl intermetallic compound was observed in the annealed samples which were previously milled for 8, 16, and 32 h. In the same specimens a minority cubic phase Fe3AlCX, anti-isomorphous with perovskite, derived from contamination of ethanol and introduced in the steel vial as a lubricant agent, was also observed. Anelasticity measurements have shown the occurrence of two main transient effects during the first thermal run. The first one occurring at 500 K in all mechanically alloyed specimens was attributed to thermally activated structural transformations, whereas the second at about 700 K was attributed to a magnetic order–disorder transition. During the second run of anelasticity measurements a relaxation peak P1 in the nanostructured B2 FeAl intermetallic compound, attributed to grain-boundary sliding mechanisms and with an activation energy of 1.8 ± 0.2 eV was observed. In specimens milled for 8–32 h a second small peak P2 at the low-temperature tail of the P1 peak was observed and tentatively attributed to a Zener-type relaxation.
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