PRODUCTION AND GRAIN STABILITY OF NANOCRYSTALLINE Fe-Si POWDERS AND THE EFFECTS OF ALUMINIUM ADDITION

The present work studied the production of nanocrystalline Fe90Si10, Fe75Si25 and Fe75Si15Al10 alloys via a high-energy ball milling technique and their grain growth responses to high-temperature annealing treatments. The grain sizes of the resulting powders were determined by X-ray diffraction peak broadening and were also confirmed by transmission electron microscopy. 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. The grain size of Fe90Si10 increased from approximately 17 nm to about 35 nm after annealing at 873 K. Fe75Si25 exhibited some stability against grain growth at low temperatures but not above 673 K. Fe75Si15Al10 grains showed better stability with no significant grain growth until 873 K. For Fe75Si25 and Fe75Si15Al10 alloys annealing at 773 K, 873 K and 973 K resulted in the formation of ordered DO3 structure.