Crystallization under electropulsing suggesting a resonant collective motion of many atoms and modification of thermodynamic parameters in amorphous alloys - art. no. 054201

For melt-spun amorphous (alpha-)Cu50Ti50 and alpha -Pd80S20, crystallizatio n 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 pro ceeds 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 te mperature during electropulsing is about 120 K for alpha -Cu50Ti50 and 50 K for alpha -Pd80Si20, respectively. One-half of the specimen volume crystal lizes after a few repetitions of electropulsing with i(d0) beyond i(d0,c) f or alpha -Cu50Ti50 and after several repetitions for alpha -Pd80Si20. We su rmise that for the density fluctuations existing in amorphous alloys, under electropulsing a high-density region undergoes a resonant collective motio n 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 phas e 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 e lectrical resistivity of a specimen decreased at the early stage of the cry stallization and then turned to increase for further electropulsing. These phenomena may be associated with changes in the thermodynamic free energy o f phases under an electric current predicted by the theoretical works. We s urmise that present electropulsing excites a resonant collective motion of many atoms and modifies the thermodynamic free energy of phases too.