KINETICS OF PHASE EVOLUTION OF ZN-FE INTERMETALLICS

The intermetallic phases, Gamma (Fe3Zn10), Gamma(1) (Fe5Zn21), delta ( FeZn7), and zeta (FeZn13), are mechanically alloyed through ball milli ng of pure elemental Fe and Zn powders under a controlled atmosphere o f argon gas. The state of the as-ball-milled materials was crystalline , except for the Gamma phase, which was amorphous. Phase-evolution kin etics through differential scanning calorimeter (DSC) measurements of the as-ball-milled powders show three characteristic transition temper atures for the Gamma(1) and zeta phases, two for the Gamma phase, and only one for the delta phase. The activation energies for the evolutio n of the milled powders to their equilibrium crystalline phases are 17 0 +/- 1, 251 +/- 2, 176 +/- 1, and 737 +/- 4 kJ/mol for the Gamma, Gam ma(1), delta, and zeta phases, respectively. These values show that th e mechanisms for the metastable-to-stable phase transition in these in termetallics are different, whereas diffusion over short distances may be part of the entire process in all cases.