Zr and Hf microalloying in an Al–Y–Fe amorphous alloy. Relation between local structure and glass-forming ability

Abstract

The effects of the addition of small amounts of Zr and Hf (0.5–3%) on the atomic structure of Al₈₈Y₇Fe₅ metallic glass were examined from extended X-ray absorption fine structure (EXAFS) experiments to better understand the influence of these microadditions on the glass-forming ability of this alloy. Measurements at the Zr K and Hf LIII absorption edges allowed the local structures around Zr and Hf atoms to be determined. The same Al environment was found for the different concentrations, consisting of a small cluster extending up to 4.5 Å around the Zr atoms and up to 6 Å around the Hf ones. Although the clustering effect is smaller in the Zr neighbourhood, a drastic shortening of the nearest Zr–Al distance is shown, providing evidence for some covalent character to the bonding, in line with the increased glass-forming ability found in the alloys made with the Zr microaddition.

Keywords:

• nanostructure
• metallic glasses
• microalloying
• Al-Y-Fe
• EXAFS
• glass-forming ability

Acknowledgements

It is a pleasure to thank all the staff of the BM30B beam line for the experiments in ESRF. We also thank A. Michalowicz for the EXAFS programs. K. F. Kelton gratefully acknowledges support from the United States Air Force Office of Scientific Research, contract AFOSR FA9550-05-1-0110 and the National Science Foundation under DMR 06-06065.