Inhibition of Electropulsing Nanocrystallization in Amorphous ZrCu under Helium Atmosphere

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Nanocrystallization of amorphous ZrCu was induced by applying a pulse current (electropulsing), which exponentially decayed from a certain initial current density (i_d0) with the time constant of 3 ms. For electropulsing, the ribbon specimen was sandwiched between high-thermal-conductive AlN (thermal conductivity κ = 170 W/m/K at 273 K) plates to remove the Joule heat. Nanocrystallization was found when electropulsing was conducted in a vacuum below 10⁻² Pa at the pulse current of i_d0 ≥ 0.6 GA/m². In contrast, electropulsing conducted under 10⁵ Pa He (κ = 0.144 W/m/K at 273 K) required i_d0 above 1.1 GA/m². Thermal conductivity and heat capacity of 10⁵ Pa He were negligibly smaller than those of the AlN plates. The increase in i_d0 for nanocrystallization with increasing He pressure indicates that He penetrated the amorphous structure to inhibit the activation of cooperative motions of many atoms and larger i_d0 is required for nanocrystallization at higher He pressure.

Fig. 5 Resistivity changes of a-Zr₅₀Cu₅₀ by electropulsing at various He pressures. The resistivity normalized by the value in as-spun state (ρ₀) is shown.