Jerzy Antonowicz

Atomic structure of Zr–Cu glassy alloys and detection of deviations from ideal solution behavior with Al addition by x-ray diffraction using synchrotron light in transmission

The atomic structure of Zr–Cu binary amorphous alloys was studied using real space pair distribution functions derived from x-ray diffraction. The structure can be modeled by an ideal solution approximation because of relatively weak Cu–Zr atomic interactions. Addition of Al to Zr–Cu metallic glasses modifies the atomic structure in the short and medium range order because of the strongly attractive interaction between Al and Zr atoms. These interactions generate strong deviations from the ideal solution behavior.

Icosahedral order in Cu-Zr amorphous alloys studied by means of X-ray absorption fine structure and molecular dynamics simulations

We have used the X-ray absorption fine structure method and molecular dynamics (MD) simulations to characterize atomic order in Cu-Zr metallic glasses (MGs). The microstructure of these MGs is described in terms of interconnected icosahedral-like clusters (superclusters) which are basic building units reproducing the stoichiometry of the system. The equilibrium MD configurations are used as an input for ab initio calculations of the extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra. The theoretical EXAFS and XANES spectra are compared with those measured for rapidly quenched glassy Cu-Zr alloys. We demonstrate that the experimental results are well reproduced by EXAFS modeling of the population of the superclusters derived from the MD configuration. The average local structural motif can be approximated by Cu-centered icosahedral-like cluster satisfying the condition of maximal local packing efficiency and approximating the system stoichiometry. The simulated XANES exhibits good agreement with experiment, indicating that the atomic order of the MD configuration is consistent with that of the real alloy structure over distances of about 1 nm.

Phase separation and nanocrystallization in Al92Sm8 metallic glass

Crystallization of Al92Sm8 metallic glass was investigated in situ using combined small-angle and wide-angle X-ray scattering (SAXS/WAXS) techniques during isothermal annealing at temperatures close to crystallization point. A continuously growing interference maximum shifting progressively towards lower angles was found to develop in SAXS regime. Simultaneously taken WAXS spectra reveal formation of fcc-Al nanocrystalline phase. The analysis of the SAXS/WAXS data indicate that amorphous phase separation is responsible for the nanocrystalline microstructure formation. The primary fcc-Al crystals nucleate inside the Al-rich amorphous regions formed during alloy decomposition and their growth is constrained by the region size.

Nanocrystallization of Al92Sm8 amorphous alloy studied in situ by real-time x-ray diffraction

We have investigated the in situ isothermal nanocrystallization kinetics of binary Al92Sm8 glassy alloy using time-resolved x-ray diffraction. From diffraction spectra parameters we have calculated the mean grain size and crystalline phase volume fraction. The results show that the average grain size does not change by more than 15% of its initial value in the course of the nanocrystallization process. The first nanocrystals contributing to the crystalline phase signal are characterized by a mean crystal size of 11 nm which increases up to 13 nm at the end of the primary crystallization stage. These results are in agreement with a TEM analysis. Our observations indicate the very significant difference in growth rate of small and large clusters. Further, they show that the transformation kinetics is governed by the nucleation rate. We conclude that diffusion controlled growth plays a minor role in the overall transformation kinetics. Possible origins of the observed crystallization behaviour are given.

Electron Structure, Stability and Nanocrystallization of Al - Based Amorphous Alloys

Electron transport studies of Al-based alloys show that the strong bonds between Al-TM and Al-Y atoms arise by mixing of 3d and 4d electron states of TM and Y atoms with the 3s and 3p states from Al. Thermal stability of the Al-RE alloys is controlled by the low diffusity of heavy RE atoms. The results allow to optimize preparation conditions for nanocrystallizing Al-based alloys with enhanced mechanical properties.