Ordering and grain growth in nanocrystalline Fe75Si25 alloy

The grain growth and ordering behaviors in nanocrystalline Fe75Si25 powders produced by mechanical alloying was studied. In the temperature range 573-703 K, the disordered α-Fe(Si) showed only limited growth with a small activation energy of 32.3 kJ mol−1. However, in the range 773-853 K ordering to DO3 structure occurred accompanied by a sharp increase in average grain size to a maximum value that depended on the temperature. A grain growth model available in the literature for nanocrystalline materials yielded a good fit to the experimental data. Activation energy of 278.9 kJ mol−1 determined using this model for grain growth is similar to that for lattice diffusion of Si in DO3 Fe3Si. The reason for the concurrence of ordering and grain growth is attributed to the Si desegregation at grain boundaries upon ordering transformation. The levels of segregation are estimated from lattice parameter measurements.