ROLE OF MATERIAL PURITY ON THE STRUCTURAL AND MAGNETIC-PROPERTIES OF RAPIDLY SOLIDIFIED FESI 6.5 WT-PERCENT ALLOYS

A study has been made on the structural and magnetic properties of rapidly quenched FeSi 6.5 wt% alloys, obtained from high purity (HP) and commercial purity (CP) master alloys and characterised upon a range of annealing treatments. Superior magnetic behavior is exhibited by the HP alloys after annealing, which correlates with enhanced growth of a favourable cube-on-face crystallographic texture. As suggested by metallographic analysis, a surface energy mechanism appears to control the evolution of such texture, with a critical role being played by solute oxygen. Mechanical strength and ductility also appear improved in the HP samples. Substantial loss of Si and weakening of the texture are however observed after high temperature annealing (T > 1200-degrees-C), with ensuing deterioration of the material soft magnetic properties. It is concluded that optimum dc and high frequency magnetic behavior of HP and CP alloy ribbons requires annealing treatments at temperatures around 1100-1150-degrees-C, where the achieved material structure provides minimum losses and maximum permeability and the high Si concentration of the as-quenched material is retained.