Andreas Kündig

Preparation of high aspect ratio surface microstructures out of a Zr-based bulk metallic glass

Silicon wafers with high aspect ratio surface microstructures, prepared by deep reactive ion etching and coated with a protective layer, are replicated into a Zr-based bulk metallic glass. Therefore, a new process route called hot mold quenching is developed. In this process, the bulk glass-forming alloy and the mold are heated to a temperature of 1350 K to allow complete wetting of the microstructured silicon mold by the melt. After a few seconds, the surface microstructures of high aspect ratio are filled by the melt completely. Mold and melt are then quenched together at a rate of 20 K/s to prevent crystallization in the Zr-Cu-Ni-Al-Ti melt. Subsequently, the wafer is removed by wet etching. Structures of 20 µm height, 8 µm width and a spacing of 1 µm have successfully been replicated into the metallic glass. Tools out of this material have a high strength, a high elastic limit and a good corrosion resistance, and meet the requirements for injection molding of polymers ideally.

Metallic foams from nanoparticle-stabilized wet foams and emulsions

We present a method to prepare metallic foams with a unique architecture of small pores and thin struts using wet foams and emulsions stabilized by metallic nanoparticles as templates.

Composition Dependence of Phase Separation and Crystallization in Deeply Undercooled Zr-(Ti-)Cu-Ni-Al Alloys

Different bulk glass forming alloys in the neighborhood of Zr 52.5 Cu 17.9 Ni 14.6 Al 10 Ti 5 (Vit105) have been investigated by differential scanning calorimetry (DSC), x-ray diffraction (XRD) and small-angle neutron scattering (SANS). Along the Ti/Al line in composition space, Zr 52.5 Cu 17.9 Ni 14.6 Al 10− x Ti 5+ x with – ≤ x ≤ +2.5, the glass transition temperature, T g , and the undercooled liquid regime (the difference between the first crystallization temperature and the glass transition temperature) continually decrease with increasing x . SANS measurements of annealed alloys show interference maxima, giving evidence for decomposition on the nanometer scale, up to a critical temperature T c . In contrast to T g , T c increases with x and thus intercepts with T g in the range –2.5 ≤ x ≤ –1.25, depending on the time scale of the experiment. At this composi- tion, significant changes in DSC traces and XRD patterns are observed. Additional isothermal DSC experiments show that the onset times for crystallization are significantly different for temperatures below and above T c . We conclude that T c , respectively the relation between T c and T g , determines the crystallization behavior and the thermal stability of these bulk metallic glasses.