Kinetics of phase evolution of Zn-Fe intermetallics

The intermetallic phases, Gamma (Fe sub 3 Zn sub 10 ), Gamma sub 1 (Fe sub 5 Zn sub 21 ), delta (FeZn sub 7 ), and xi (FeZn sub 13 ), are mechanically alloyed through ball milling of pure elemental iron and zinc powders under a controlled atmosphere of argon gas. The state of the as-ball-milled materials was crystalline, except for the Gamma phase, which was amorphous. Phase-evolution kinetics through differential scanning calorimeter (DSC) measurements of the as-ball-milled powders show three characteristic transition temperatures for the Gamma sub 1 and xi phases, two for the Gamma phase, and only one for the delta phase. The activation energies for the evolution of the milled powders to their equilibrium crystalline phases are 170plus/minus1, 251plus/minus2, 176plus /minus1, and 737plus/minus4 kJ/mol for the Gamma , Gamma sub 1 , delta , and xi phases, respectively. These values show that the mechanisms for the metastable-to-stable phase transition in these intermetallics are different, whereas diffusion over short distances may be part of the entire process in all cases.