Nanocrystalline transformation and inverse transformation in metallic glasses induced by electropulsing

Abstract

Electropulsing by means of discharge of a condenser with the decay time (τ) of ms causes the athermal crystallization of metallic glasses when the initial current density (id0) is higher than the threshold value (ido.c). It is indicated that the major local amorphous structures in Zr50Cu50 are the amorphous structures with the short range order (SRO) similar to crystalline cubic (c) ZrCu which is the equilibrium crystalline phase above 988 K, although the mixture of crystalline Zr 2Cu and Zr7Cu10 is the equilibrium phase below 88 K. Electropulsing tests on Zr50Cu50, Zr 50Cu40Al10 and Zr50Cu 35Al10Ni5 metallic glasses indicate that the amorphous structures with SRO similar to cZrCu are the major local amorphous structures in these metallic glasses, and their volume fractions decrease in the order of Zr50Cu50, Zr50Cu40Al 10 and Zr50Cu35 Al10Ni5. The amount of the amorphous structures with SRO similar to cZrCu may govern the thermal stability of these metallic glasses. Further in Zr50Cu 50 metallic glasses, the inverse transformation from the electropulsing-induced fine crystallites to the amorphous phase for subsequent electropulsing with increasing id0, and the Ostwald-ripening-like phenomenon under electropulsing were observed. © 2007 The Japan Institute of Metals.