Dresden 2006 – wissenschaftliches Programm

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MM: Metall- und Materialphysik

MM 45: Mechanical Properties III

MM 45.4: Vortrag

Freitag, 31. März 2006, 13:15–13:30, IFW A

Room-temperature embrittlement of Mg-based amorphous alloys — •A. Castellero, D.I. Uhlenhaut, and J.F. Löffler — Laboratory of Metal Physics and Technology, ETH Zürich, Wolfgang Pauli Str. 10, 8093 Zürich, Switzerland

Mg-Cu-Y alloys can be amorphised in a wide range of compositions. When these alloys are produced in bulk form they exhibit high mechanical strength but no ductility. Rapidly quenched ribbons and thin foils show plastic deformation upon bending. However, a dramatic deterioration in mechanical properties is observed after aging at room temperature. A sharp transition from ductile to brittle behaviour can be observed in Mg65Cu25Y10 a few hours after the alloy has been produced. The process becomes slower when Cu is substituted by Mg. Corresponding to this time-dependent embrittlement, differential scanning calorimetry (DSC) curves show a reduction in the relaxation enthalpy that is associated with a structural relaxation (i.e. annihilation of free volume) of the metallic glass. Oxidation as a cause of this embrittlement has been ruled out, since the same behaviour is observed when the samples are stored in a protective atmosphere. The bent as-quenched samples exhibit shear bands on the surface, indicating that the material is able to deform plastically. The aged metallic glass exhibits only elastic deformation, followed by catastrophic failure at a certain critical bending strain which progressively decreases with time. The mechanical properties and the deformation mode were characterized in detail as a function of time.