Curie temperature behaviour at relaxation and nanocrystallization of Finemet alloys

Dependence of Curie temperature (Tc) on time and temperature of annealing for Finemet-type amorphous alloys is studied by DSC. Structural relaxation of an amorphous phase at annealing is accompanied by increase of Tc. The sigma-shaped time dependencies, however, are not characterized by the definite final value of Tc: long-term annealing of amorphous phase results in continuation of slow increase of Tc for every temperature. Apparent values of activation energy of relaxation were evaluated from the Tc time-temperature dependencies. It is found that the average value of activation energy increases with progress of the relaxation process. Correlation of the Tc data with structural alterations reflects redistribution of components in amorphous phase during annealing. Further increase of the annealing temperature results in precipitation of alpha-Fe(Si) nanograins in an amorphous matrix, that accompanied by gradual degradation of corresponding to Tc heat capacity peak. DSC measurements of Tc allow to detect the starting moment of amorphous phase crystallization. (C) 2011 Elsevier B.V. All rights reserved.