The influence of elastic strain on the early stages of decomposition in Cu-1.7at% Fe.

The initial stage of decomposition of homogenized Cu-1.7at% Fe at 722K was investigated by means of field ion microscopy (FIM), atom probe tomography (APT) and computer-assisted field ion image tomography (cFIIT). The agglomeration of atoms depending on time could be investigated and the growth of precipitates with a diameter of few nanometers was observed during ongoing nucleation. For the cFIIT measurements, an improved reconstruction algorithm was developed. Employing cFIIT in combination with FIM images, alignments of precipitates mainly in 100 directions were found. Besides, a general experimental concept to evaluate strain-related effects on the position of the proximate precipitate will be introduced. These analyses of the APT and cFIIT data show tendencies of a preferred 100 directed configuration as well. This effect can be associated with the elastic anisotropy of the Cu matrix (f.c.c.) to accommodate the volume misfit of precipitates. In accordance with previous model calculations, a preferred nucleation in 100 directions with respect to existing clusters can be concluded. For such cluster arrangements strain energy reduction is largest for precipitates adapting their sizes. Thus, additional stabilization against coarsening can be inferred for 100 alignments which result in the observed effects.