Production and annealing of nanocrystalline Fe–Si and Fe–Si–Al alloy powders

Nanocrystalline Fe90Si10, Fe75Si25, and Fe75Si15Al10 alloy powders were produced by high-energy planetary ball milling, starting from elemental powders. The resulting powders were annealed at various temperatures for 30 min and their grain sizes were determined by X-ray diffraction peak broadening using the Williamson–Hall approximation and confirmed by transmission electron microscope (TEM) observation. A minimum crystallite size of 13–17 nm could be achieved in Fe90Si10, Fe75Si25, and Fe75Si15Al10 alloys. The lattice parameters of as-milled Fe90Si10, Fe75Si25, and Fe75Si15Al10 attained minimum values of about 0.2860, 0.2842, and 0.2862 nm, respectively after 60 h, and thereafter remained constant for prolonged milling times. Annealing at 873 K increased the grain size of Fe90Si10 from approximately 17 nm to about 35 nm. Fe75Si25 exhibited some stability against grain growth at low temperatures but not above 673 K. Fe75Si15Al10 grains were more stable with no significant grain growth until 873 K. For Fe75Si25 and Fe75Si15Al10 alloys annealing at 773, 873, and 973 K resulted in the formation of ordered DO3 structure with long-range order (LRO) parameters ranging from 0.64 to 0.71. The internal strains of all three compositions decreased steadily with annealing from the range 0.63–0.32% to the range 0.23–0.07%.