High Temperature AL-Nanocrystal Alloy Synthesis
Final rept. 1 Jun 1997-31 May 2000
WISCONSIN UNIV-MADISON DEPT OF MATERIALS SCIENCE AND ENGINEERING
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Aluminum-rich metallic glasses containing transition metals and rare earth elements have been found to yield finely mixed microstructures of Al nanocrystals embedded in an amorphous matrix and exhibit enhanced fracture strength with several percent strain. Upon primary crystallization of melt spun ribbons, this novel microstructure comprised of a high particle density 1020 m3 of Al nanocrystals 2Onm in an amorphous matrix develops and offers exceptional strength 1500MPa and high temperature stability 533K. Numerical modeling based upon the size distribution of the Al nanocrystals after isothermal annealing is applied to study the nucleation kinetics in the metallic glasses. In addition to the kinetic study of primary nanocrystallization, the glass transition temperature T2 has been assessed in Al-7atY-5atFe and Al-8atSm alloys. In usual calorimetric measurements, the thermal response of the primary crystallization often obscures the observation of the signal corresponding to the glass transition. As a result, T2 is often assumed to be near the onset of the primary crystallization reaction TxAl However, it has been demonstrated by modulated-temperature calorimetry that this assumption does not apply strictly to the metallic glasses under study. The thermal stabilization of the microstructure by the occurrence of diffusion field impingement allows for the observation of the glass transition of the remaining amorphous phase in the matrix by modulated DSC. The reliable assessment of the glass transition temperature provides not only a ftindamental basis for the kinetics analysis, but also an important parameter in designing suitable annealing treatments that allow for the development of desired microstructures to yield optimized properties.
- Properties of Metals and Alloys