Transmission electron microscopy investigations of ordered Zr3Al

Zr₃Al is an ordered fcc alloy of the L1₂ type. The ordered phase appears to be very stable thermally as it has not been possible to disorder Zr₃Al by quenching. It is possible, however, to disorder Zr₃Al by irradiation. In deformed Zr₃Al the superlattice dislocations were observed to be extended, i.e. they consisted of intrinsic stacking faults on {111} bounded by partial dislocations. _ The total Burgers vector is of the type <110> and the superlattice dislocations have dissociated as follows: $\text{«110}\text{a}\text{?}\text{> →}\text{1}\text{3}\text{«211}\text{a}\text{?}\text{> +}\text{1}\text{3}\text{«12}\text{1}\text{?}\text{a}\text{?}\text{>}$. During high-temperature annealing of the deformed material, dislocation networks were produced in which all of the dislocation nodes were extended; hence intrinsic and extrinsic stacking faults must alternate at the nodes. Weak beam images were obtained of long and relatively straight dislocation lines in annealed Zr₃Al in order to obtain information on the equilibrium width of the extended dislocations.