Local order and nanostructure induced by microalloying in Al–Y–Fe amorphous alloys
Résumé
Extended X-ray absorption fine structure (EXAFS) measurements show that the dramatic improvement in glass formation in Al–Y–Fe alloys made with a small additions of Ti and V has a structural origin. The EXAFS spectra show that a well-defined Al atomic structure exists around the V and Ti atoms that is different from that around the major constituent Al, Y and Fe atoms, even at the lowest concentrations. The local Ti– and V–Al clusters have a size of about 1 nm. Around the V atoms, the local order can be described by a small face centered cubic cluster. Around the Ti atoms, the local structure seems to evolve from a face centered cubic nano-cluster towards a body centered cubic one when the concentration increases from 0.5% to 2%. These measurements demonstrate that Ti and V form strong interactions with Al, with a significant shortening of the bond length. This should raise the barrier for nucleation of α-Al, explaining the greater stability of the glasses containing Ti or V.