Effects of electric current on solid state phase transformations in metals

The influence of an electric current on the following solid state transform ations in metals are considered: (1) intermetallic compound formation and g rowth in diffusion couples, (2) precipitation, (3) crystallization of amorp hous alloys and (4) recrystallization and grain growth of cold worked metal s. The formation and growth of intermetallic compounds were in qualitative accord with electromigration theory. Regarding precipitation, an electric c urrent can either enhance or retard the precipitation rate, depending on th e alloy, the current density and its frequency. Important factors appear to be the effect of current on the quenched-in vacancies and the presence of an internal stress. Both a continuous d.c. current and high current density electropulsing enhanced the crystallization rate of amorphous alloys. The effects are greater than can be explained by simple electromigration theory and suggest the cooperative motion of a larger number of atoms. Electropul sing enhanced the recrystallization rate of cold worked metals, but retarde d subsequent grain growth. Enhancement of the recrystallization rate result ed mainly from an increase in the pre-exponential factor of the Arrhenius r ate equation, which is considered to refer to the nucleation rate. Retardat ion of subsequent grain growth resulted from a lower residual dislocation d ensity within the newly-formed grains. (C) 2000 Elsevier Science S.A. All r ights reserved.