Transformation to Nanocrystallites in Amorphous Alloys Induced by Resonant Electropulsing

Abstract

The electropulsing-induced low temperature crystallization (e-LTC) of marginal amorphous (a-) alloys, a-Cu₅₀Ti₅₀ and a-Pd₈₀Si₂₀, and a bulk amorphous alloy, a-Zr₆₀Cu₃₀Al₁₀, was investigated by electropulsing at room temperature (RT) and in liquid nitrogen (LN₂). Electropulsing was made by means of discharge of a condenser which is characterized by the initial current density, i_d0, and the decay time, τ, where the frequency of the principal constituent Fourier component of the electropulsing is 1⁄2πτ. The range of i_d0 was between 10⁸ and 10¹⁰ A/m² and that of τ was between 0.1 and 20 ms. For all the amorphous alloys, the e-LTC took place during single electropulsing with i_d0 beyond the threshold current density, i_d0,c, where i_d0,c was a function of τ. The maximum specimen temperature during the e-LTC was, e.g., 200 K for electropulsing in LN₂, indicating that the e-LTC is associated with an athermal process, the resonant collective motion of the relatively high density region here. The dependence of i_d0,c on τ found for electropulsing in LN₂ showed good agreement with that observed at RT, indicating that the density fluctuation responsible for the e-LTC was that frozen at the glass transition temperature. The transmission electron microscopy observation revealed that crystallites formed by the e-LTC showed crystallographic alignment with each other, suggesting that the transformation of the relatively high density regions to a crystalline phase took place. The underlying mechanism of the e-LTC was discussed.