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

Abstract

For melt-spun amorphous (a-)Cu 50 Ti 50 and a-Pd 80 Si 20 , 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 in between 2 and 0.1 ms, where a specimen was sandwiched by AlN/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 d0,c is a function of and shows a minimum value of 1.4ϫ10 9 A/m 2 at ϳ2 ms for a-Cu 50 Ti 50 and 2.6ϫ10 9 A/m 2 at ϳ0.9 ms for a-Pd 80 Si 20 , where the maximum increase in temperature during electropulsing is about 120 K for a-Cu 50 Ti 50 and 50 K for a-Pd 80 Si 20 , respectively. One-half of the specimen volume crystallizes after a few repetitions of electropulsing with i d0 beyond i d0,c for a-Cu 50 Ti 50 and after several repetitions for a-Pd 80 Si 20. 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 a-Pd 80 Si 20 , 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 a-Cu 50 Ti 50 and a-Pd 80 Si 20 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.

Electron Irradiation Induced Crystallization of the Amorphous Phase in Zr-Cu Based Metallic Glasses with Various Thermal Stability

“…The crystallization of the amorphous phase is induced not only by thermal annealing but other external factors such as electron irradiation, 14,15) focused ion beam (FIB), 16) electropulsing 17,18) and high pressure. 19) We found that electron irradiation can induce nanocrystallization of an amorphous phase in metallic glasses in which nanostructure cannot be easily realized by thermal annealing.…”

Nanocrystallization of Cu<SUB>50</SUB>Zr<SUB>45</SUB>Ti<SUB>5</SUB> Metallic Glass Induced by Electron Irradiation

“…Crystallization of the glassy phase is induced not only by heat treatments but by other methods such as electron irradiation, [9][10][11] ion irradiation, 12) electropulsing 13) and high pressure. 14) It has been demonstrated that electron irradiation can induce nanocrystallization in metallic glasses in which nanoscale structures cannot easily be realized by heat treatments.…”

Ultrasound-Induced Structural Anomaly of Supercooled Liquid in Some Bulk Metallic Glasses

“…Mizubayashi et al [18][19][20][21][22][23][24] have investigated effects of passing electric current on the structural relaxation and crystallization of some kinds of amorphous alloys, which shows that crystallization is very much accelerated by the electropulsing far below the normal crystallization temperature without the pulsing. Recently, elastic and anelastic properties of Zr 55 Al 10 Ni 5 Cu 30 25) and Pd 40 Ni 40 P 20 26) bulk metallic glasses around T g have been studied with the electromagnetic acoustic resonance (EMAR) method within the frequency range of 300-1500 kHz.…”