Regensburg 2004 – wissenschaftliches Programm
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M: Metallphysik
M 9: Flüssige und amorphe Metalle III
M 9.5: Vortrag
Montag, 8. März 2004, 17:30–17:45, H16
Quasicrystal Formation in Decomposed V4 Metallic Glass — •S. Mechler, M. Wollgarten, N. Wanderka, and M.-P. Macht — Hahn-Meitner-Institut Berlin, Glienicker Strasse 100, 14109 Berlin
The bulk metallic glass Zr46.75Ti8.25Ni10Cu7.5Be27.5 (V4) is one of the most stable metallic glasses. The stability of this glass has been attributed to a strong long range decomposition before crystallization occurs. In order to characterize the first stages of crystallization and to relate the crystallization to the decomposition of the glass, the early stages of these phase transformations are investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM) and the 3-dimensional atom probe (3-DAP). After annealing of the glass at 643 K for 6 h and at 593 K for 21 d an icosahedral quasicrystalline phase is detected in the glass by XRD. After annealing of the glass at 573 K for 42 d the alloy is still amorphous and a decomposition of the initially homogeneous glass is observed by TEM and 3-DAP.Heating of such a decomposed glass in the DSC with a heating rate of 4 K/min up to 709 K, leads to the formation of a icosahedral quasicrystalline phase, which is different in composition and its quasilattice constant from the quasicrystals after isothermal annealing. Even after prolonged pre-annealing (84 d) at 573 K the alloy stays still amorphous and also icosahedral quasicrystals form after the DSC treatment. However, also these quasicrystals differ in composition and quasilattice constants from both phases quoted above. One prominent feature of all three quasicrystalline phases is their strong depletion of Be and enrichement in Ti compared to the initial glass matrix.