Transformation to Nanocrystallites in Amorphous Alloys Induced by Resonant Electropulsing

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, id0, and the decay time, .TAU., where the frequency of the principal constituent Fourier component of theelectropulsing is 1/2.PI..TAU.. The range of id0 was between 10\u278\u27 and 10\u2710\u27 A/m\u272\u27 and that of .TAU. was between 0.1 and 20 ms. For all the amorphous alloys, the e-LTC took place during single electropulsing with id0 beyond the threshold current density, id0,c, where id0,c was a function of .TAU.. The maximum specimen temperature during the e-LTC was, e.g., 200 K forelectropulsing 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 id0,c on .TAU. 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 formedby 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