Speaker
Description
Metastable solid materials such as amorphous or nanocrystalline alloys, supersaturated solid solutions, high-temperature or high-pressure phases persisting at normal conditions, have been of great interest due to a possibility to explore novel structures with unknown properties. These materials are kinetically determined and can be therefore synthesize only by non-equilibrium processes. Magnetron sputtering is thus a suitable technique for their preparation as thin films.
The present study focuses on preparation of thin-film metallic alloys from the binary W–Zr system by non-reactive magnetron sputtering and systematic investigation of their structure, properties, and thermal behavior at elevated temperature. The films were sputter-deposited in argon gas using two unbalanced magnetrons equipped with a W and Zr target, respectively. The elemental composition of the films was controlled in a very wide composition range (0 – 100 at.% Zr) by varying the deposition rate from individual targets.
Using this PVD method, we were able to prepare W–Zr thin-film alloys with several metastable structures in respect to the equilibrium phase diagram. Up to 24 at.% Zr, the structure of the films is characterized by a supersaturated bcc α-W(Zr) solid solution with a highly oriented structure, columnar microstructure, enhanced hardness and very low residual stress. In the range between 33 and 83 at.% Zr, an amorphous structure with features indicating metallic glass behavior is observed. These films exhibit a very smooth surface, moderate compressive stress, and constant electrical resistivity. Above 83 at.% Zr, high-temperature bcc β-Zr(W) and high-pressure hcp ω-Zr(W) phases with an enhanced hardness are prepared. Moreover, a very interesting dual structure with crystalline columnar submicrometer-sized conical domains surrounded by a metallic glass is formed at 28 at.% Zr. Thermal stability and oxidation behavior of these metastable structures will be discussed as well.
| Speaker Country | Czech Republic |
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