Thermal and microstructural dependence of the initial permeability of Co60Fe18Nb6(B,Cu)16 alloys

The thermal and microstructural dependence of the initial permeability of Co60Fe18Nb6B16−yCuy (y = 0, 1) alloys have been studied. The comparison of kinetics and microstructural data of the two compositions indicate the existence of a Cu-clustering phenomenon prior to the nanocrystallization for the alloy with Cu. These data are correlated with the evolution of the permeability as the devitrification progresses. From the technological point of view, samples treated up to the final stages of nanocrystallization exhibit temperature coefficients of the initial permeability one order of magnitude better than those of conventional nanocrystalline alloys or Mn-ferrites and a maximum temperature of applicability ∼300 K higher.