Crystallization under electropulsing suggesting a resonant collective motion of many atoms and modification of thermodynamic parameters in amorphous alloys

For melt-spun amorphous (alpha-)Cu50Ti50 and alpha -Pd80S20, crystallization under electropulsing was studied by means of the discharge of a condenser with initial current density i(d0) of the order of 10(9) A/m(2) and decay time tau in between 2 and 0.1 ms, where a specimen was sandwiched by AIN/BN substrates to minimize an effect of joule heating. The crystallization proceeds during electropulsing when i(d0) is higher than the threshold i(d0,c) Here i(d0c), is a function of tau and shows a minimum value of 1.4 x 10(9) A/m(2) at tau similar to2 ms for alpha -Cu50Ti50 and 2.6 x 10(9) A/m(2) at tau similar to0.9 ms for alpha -Pd80Si20, where the maximum increase in temperature during electropulsing is about 120 K for alpha -Cu50Ti50 and 50 K for alpha -Pd80Si20, respectively. One-half of the specimen volume crystallizes after a few repetitions of electropulsing with i(d0) beyond i(d0,c) for alpha -Cu50Ti50 and after several repetitions for alpha -Pd80Si20. We surmise that for the density fluctuations existing in amorphous alloys, under electropulsing a high-density region undergoes a resonant collective motion as a whole, which induces migrational motions of atoms in the low-density matrix around it. For alpha -Pd80Si20, it is observed that an unknown phase was formed in the early stage of the crystallization under electropulsing and disappeared after further electropulsing. It is also found for alpha -Cu50Ti50 and alpha -Pd80Si20 that for electropulsing with high i(d0), the electrical resistivity of a specimen decreased at the early stage of the crystallization and then turned to increase for further electropulsing. These phenomena may be associated with changes in the thermodynamic free energy of phases under an electric current predicted by the theoretical works. We surmise that present electropulsing excites a resonant collective motion of many atoms and modifies the thermodynamic free energy of phases too.