Determination of temperature regimes for annealing of ferromagnetic amorphous wires obtained by the Ulitovsky – Taylor method during heating by direct current flow

The direct current (dc) heating effect of ferromagnetic amorphous wires (AW) on the electromagnetic properties of the serial Co-based alloy, Co – Fe – Cr – Si – B, is investigated. The Ulitovsky – Taylor method was used to produce AW with diameters D = 40, 70, 82, 98, 123, and 145 μm in a glass shell, that was removed mechanically by elastic bending on a laboratory bench. The developed in situ method of stepwise cyclic dc heating of AW of various diameters enables to choose the optimal values of the current (Ia) for carrying out the selected modes that maximize the magnetic properties. AW electromagnetic properties were monitored by registering the amplitude of the intrinsic electromagnetic signal of electromotive force (EMF) of the AW sample under study. Since reliable direct measurements of AW temperature (Ta) when passing the current (Ia) quite an undertakings, we used indirect method of AW heating temperature estimation by establishing the relationship Ta = f (Ia). For the AW specified diameters, the direct current values were experimentally determined, which ensure optimal heat treatment in the range of temperature stability of the amorphous phase, up to the crystallization temperature, Tx. A calibration curve was constructed using reference temperature points, i.e. Tx and the Curie temperature (Tc). The proposed technique for calibration graph construction I = f(D) may be used for different AWs that have different diameters and same composition; it allows one to determine the modes of current annealing required for the best EMF amplitude values of amorphous wires of the given diameter, up to 100 μm.