Defect structures in low stacking fault energy CuGe solid solutions

Abstract

The defects present in metastable CuGe alloys after slow cooling or quenching from the solution temperature have been investigated by conventional electron microscopy techniques. The defect configurations present after low temperature aging treatments designed to avoid the onset of h.c.p. phase precipitation have also been studied. The principal defects in slowly cooled alloys are intrinsic stacking faults bound by Shockley partials, whereas quenched alloys exhibit more “ragged” Shockley partials and “black spot” defects. Excess vacancies or vacancy-solute clusters present after quenching migrate during aging to form defects, the exact nature of which could not be identified for temperatures below 200 °C but were identified as stacking fault tetrahedra as the aging temperature was raised. Defect-free zones were observed adjacent to grain boundaries, non-coherent annealing twin boundaries and some partial dislocations, indicating that such regions can act as effective sinks for vacancy annihilation.