Regensburg 2002 – wissenschaftliches Programm

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M: Metallphysik

M 12: Amorphe und metastabile Metalle III

M 12.7: Fachvortrag

Dienstag, 12. März 2002, 16:00–16:15, H4

Development of nanocrystals in amorphous Al-alloys — •Nancy Boucharat¹, Harald Rösner¹, John H. Perepezko², and Gerhard Wilde¹ — ¹Forschungszentrum Karlsruhe, Institut für Nanotechnologie, Postfach 3640, D-76021 Karlsruhe — ²University of Wisconsin-Madison, Department of Materials Science and Engineering, 1509 University Avenue, Madison WI 53706, USA

Many Al-based metallic glasses such as Al₉₂Sm₈ and Al₈₈Y₇Fe₅ undergo a partial transformation upon heating that leads to a fine-scaled dispersion of Al-nanocrystals embedded in an amorphous matrix. These materials exhibit a high tensile strength that is directly related to the high number density of Al-nanocrystals. Yet, the origin of the nanocrystallization process is still discussed controversially. Calorimetric and structural investigations after processing pathway variations indicate that the nanocrystals originate from quenched-in nuclei. To study the kinetics of the nanocrystallization in detail, nanocrystal size distributions have been determined after continuous heating and isothermal annealing treatments. Additionally, isothermal micro-calorimetry investigations have been conducted to monitor the early stages of nanocrystal development directly on long time scales. The results are compared to crystallization kinetics models and discussed with respect to the nature of the underlying nucleation and growth mechanisms.