An NMR Study of Metallic Glasses
Final rept. 1 Jun 96-31 Aug 99
NORTH CAROLINA UNIV AT CHAPEL HILL
Pagination or Media Count:
The mechanisms of atomic transport in the supercooled liquid state SLS and the nature of glass transition have been challenging problems for decades. It is believed that collective atomic motion plays a key role in the dramatic slow-down of kinetics near the glass transition temperature Tg. Thus, understanding the mechanisms of atomic transport is directly linked to the understanding of the glass forming ability of metallic alloys. Measurements on both macroscopic and microscopic scales are required for the understanding of atomic motions in SLS and glasses. We have developed a nuclear magnetic resonance technique, the Be-9 spin alignment echo technique SAE, to probe slow atomic motions on microscopic scales. Systems of focus are Vitreloy 1 and Vitreloy 4, two of the Zr-Ti-Ni-Cu-Be bulk metallic glasses with extraordinary glass forming ability. By combining SAE and diffusion measurements it was revealed that long-range transport of Be atoms in the SLS is due to two diffusion processes, one of these is single-atom hopping assisted by thermal fluctuation of spread-out free volume. However, collective motion of atomic clusters dominates in the SLS. Further understanding of the influence of composition and processing on such atomic motions could lead to the improvement of glass forming ability.
- Ceramics, Refractories and Glass
- Atomic and Molecular Physics and Spectroscopy