Influence of Nanocrystallization in the Electrochemical Behaviour of Fe_((73.5-x))Cu_1Nb_3Si_(13.5)B_9Cr_(x(0-5)) Finemet Type Alloy

摘要

The potentiodynamic polarization curves in 2N HCl solutions, before and after nanocrystallization of Fe_((73.5-x))Cu_1Nb_3Si_(13.5)B_9Crx_((0.5)) amorphous alloys, are reported in relation to the microstructural changes and alloy composition. Polarization measurements show that when the chromium content in the alloy is ≥3 at% Cr in Fe_((73.5-x))Cu_1Nb_3Si_(13.5)B_9Crx_((0.5)) nanocrystalline alloys significantly decrease the current density at the active-passive transition, i_(crit). In nanocrystalline Finemet alloy (without chromium), the polarization experiment proceeds at least in two steps. After the first step, the TCP analysis of the working electrolytes showed that only iron dissolves into the solution and therefore, the nanocrystalline phase of alloys containning nanocrystalline Fe(Si) phase within a residual amorphous matrix, is more active and should be preferentially dissolved leaving the passivated amorphous phase on the specimen surface.