STACKING-FAULT ENERGY AND PHASE-STABILITY IN LONG-RANGE ORDERED CU-ZN-AL ALLOYS

The close-packed martensitic phases in Cu-Zn-Al alloys can be described as an f.c.t. ordered lattice into which stacking faults are introduced. The stacking fault energy would be essentially the same as for the disordered alpha-phase, but is reduced due to an additional lattice distortion which depends on the ordering energy of the fc.t. lattice. In the 2 H martensite with a stacking fault on each second plane, the stacking faults interact, leading to a small increase in energy. Thus, in these ordered martensites the stacking fault energy depends not only on the composition, but also on the ordering energy and on the lattice distortion associated with it. These observations can be relevant to understand the dislocation mobility in other fc.t. long-range ordered alloys.