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%.