The mechanical properties and dislocation structure of the Gamma intermetallic phase in the Fe-Zn system

Polycrystalline specimens of single phase of the Gamma-Fe3Zn10 phase in the Fe-Zn system have been prepared and deformed in compression between 250 and 700 degrees C. The thermal activation parameters have been measured and dislocation structures examined by transmission electron microscopy. Below 250 degrees C the Gamma-phase is brittle, but above 300 degrees C it is ductile. Most of the dislocations activated under the action of an applied stress have the Burgers vectors parallel to [111] over the temperature range studied. The Burgers vector of dislocations introduced at 300 and 450 degrees C is b = (a/2)[111], where a = 0.9005 nm (the lattice constant of the Gamma-phase). On the other hand, the Burgers vector of dislocations introduced above 600 degrees C is either b = (2a/3)[111] or b = (a/3)[111]. The activation volume at low temperatures (300 and 450 degrees C) is estimated to be about 200 Angstrom(3), and it is suggested that the dislocations activated at low temperatures are dissociated into partials whose Burgers vector is 1/6[111]. Some evidence for the dissociation is obtained from the weak-beam electron micrographs. The reason why b is different at high temperatures and low temperatures is also discussed.