Al-based nanocrystalline alloys have attracted substantial interest due to their outstanding mechanical properties. In
order to contribute to an atomistic understanding of the interfacial structure and processes during the various states
of nanocrystallization, the present project will deal with studies of interfacial free volumes in Al-Sm and Al-Y-Fe
alloys by means of positron lifetime and coincident Doppler broadening spectroscopy. The combination of these
two techniques yields unique and novel information on both the size of free volumes and the chemical nearestneighbourhood
of the free volumes which cannot be obtained otherwise. Since positrons escaping from the
nanocrystallites are trapped predominantly at the interfaces between the nanocrystallites and the intergranular
amorphous phase, positron annihilation is particularly well suited for studying of free volumes at the nanocrystal
glass interfaces, the chemistry of which is a major factor of the nanocrystallization process of Al-based alloys.
The following major issues will be dealt with:
Study of the solute pile-up at the crystal amorphous interfaces which are formed between the Al
nanocrystallites and the amorphous matrix.
Study of the variation of the size and the chemistry of free volumes with processing routes of
nanocrystallization (i.e., thermally induced or deformation-mediated) and with state of processing (i.e.,
variation with annealing and deformation).
Variation and optimization of the alloy composition with respect to a high number density of primary
crystallites, a high volume fraction of nanocrystallites, and a high thermal stability.
The atomic-scale studies on free volumes obtained from positron annihilation will be combined with a structural
characterization using x-ray diffraction (XRD) and transmission electron microscopy (TEM). For an unambiguous
assessment of the potentials of coincident Doppler broadening as new analytical method for studying of interfaces
in multicomponent complex materials, the results will be compared with studies of analytical high-resolution