Ordering of Fe-Si phases

The microstructure of Fe-Si alloys containing 8 and 15.5 at % Si and heat-treated between 550 and 1200°C is studied by transmission electron microscopy, and the phase composition of alloys containing 19 and 23 at % Si is determined by x-ray diffraction. The Fe-15.5 at % Si alloy heat-treated above 700°C is found to consist of a disordered solid solution and B2 phase. The B2 particles can be thought of as portions of {100} layers consisting entirely of Si atoms and sandwiched between {100} layers of Fe atoms, that is, as a two dimensional phase. At t 675°C, a compositionally modulated microstructure develops in which the Si-enriched zones have the Fe₃ Si stoichiometry and DO₃ structure. At high temperatures, the Fe-19 at % Si alloy consists of the and B2 phases, and the Fe-23 at % Si alloy consists of the and DO₃ phases. These findings are at variance with the generally accepted Fe-Si phase diagram.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 28–35.Original Russian Text Copyright © 2005 by Ustinovshchikov, Sapegina.