Structural and Thermal Study of Nanocrystalline Fe-Al-B Alloy Prepared by Mechanical Alloying

Nanostructured iron-aluminum alloy of Fe-25 at. pct Al composition doped with 0.2 at. pct B was prepared by mechanical alloying. The phase transformations and structural changes occurring in the studied material during mechanical alloying and during subsequent heating were investigated by SEM, XRD, and DSC techniques. The patterns so obtained were analyzed using the Rietveld program. The alloyed powders were disordered Fe(Al) solid solutions and Fe2B boride phase. The Fe2B boride phase is formed after 4 hours of milling. The crystallite size reduction to the nanometer scale (5 to 8 nm) is accompanied by an increase in lattice strains. The powder milled for 40 hours was annealed at temperatures of 523 K, 823 K, 883 K, and 973 K (250 °C, 550 °C, 610 °C, and 700 °C) for 2 hours. Low temperatures annealing are responsible for the relaxation of the disordered structure, while high temperatures annealing enabled supersaturated Fe(Al) solid solutions to precipitate out fines Fe3Al, Fe2Al5, and Fe4Al13 intermetallics and, also the recrystallization and the grain growth phenomena.