Effect of annealing on structural and magnetic properties of Al substituted nanocrystalline Fe-Si-Co alloy powders

We report effects of annealing and substitution of Al on structural and magnetic properties of nano crystallineFe(80-x)Al(x)Co(5)Si(15) (x=0-10) alloy powders prepared by mechanical alloying process using a planetary ball mill technique. All the as-milled powders exhibit non-equilibrium solid solution of alpha-Fe (Si,Co,Al). While the average size of crystals decreases, the lattice constant and dislocation density increase with increasing Al content. On the other hand, the annealing at elevated temperatures increases the size of the crystals and decreases the dislocation density. In addition, the substitution of Al in FeAICoSi alloy powders controls growth of the crystals during annealing. As a result, coercivity (H-C) of the annealed powders decreases considerably. However, the variation in H-C is dominated by the dislocation density. Fe70Al10Co5Si15 powder annealed at 900 degrees C exhibits improved magnetic properties (H-C similar to 14 Oe and moderate magnetization of 160 emu/g) due to optimum nanocrystalline microstructure with fine nanocrystals (similar to 18 nm) and reduced dislocation density. Systematic correlations observed between structural and magnetic properties for Fe80-xAlxCo5Si15 powders reveal a promising approach to control the growth of the crystals in the annealed nanocrystalline alloys and to improve the magnetic properties of mechanically alloyed Fe Si based nanocrystalline alloys by adding suitable substituting elements. (C) 2016 Elsevier B.V. All rights reserved.