Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft Wissenschaftliche Berichte FZKA 7205 Nonequilibrium Processing of Amorphous and Nanostructured Materials Guru

Content Provider	Semantic Scholar
Author	Dinda, Gargi
Copyright Year	2006
Abstract	Nanostructured materials have attracted great interest in recent years because of the unusual mechanical, electrical and optical properties endowed by confining the dimensions of such materials and because of the combination of bulk and surface properties to the overall behaviour. There is continued interest in finding cost effective and simpler ways to fabricate nanostructured materials, even though research groups have been investigating possibilities for the past three decades. Here we describe a simple but very useful approach – so-called repeated cold-rolling – to synthesize large quantities of nanostructured materials at ambient temperature. In the present work, massive nanocrystalline samples of Ti, Zr and Pd with average grain sizes below 100 nm and Ni with a grain size less than 10 nm have been synthesized at ambient temperature by repeated cold-rolling. Such small grain sizes have not been obtained for pure metals by any other severe plastic deformation technique. The development of the microstructure in dependence of deformation was investigated by X-ray diffraction, followed by the characterization of their morphology in cross section by scanning electron microscopy and transmission electron microscopy and the grain refinement mechanisms were analyzed. The mechanical responses of the nanostructured materials produced by repeated cold-rolling are studied by nanoindentation and Vickers hardness test. The highest hardness was observed for severely cold-rolled Ni of grain sizes less than 50 nm. Aside from the opportunity to obtain nanocrystalline bulk samples, the processing pathway also allows for synthesizing bulk amorphous materials. Since the discovery of solid state amorphization reactions, mechanical alloying processes have been extensively investigated. However, the exact mechanisms of mechanically induced amorphization are not yet firmly established. By repeated cold-rolling, we were able to synthesize fully amorphous samples of different binary Cu-Zr, Cu-Ti, Ni-Zr, ternary TiZr-Cu and quaternary Ti-Zr-Cu-Ni and Zr-Al-Cu-Ni alloy systems at ambient temperature starting from pure elemental foils. The key issue to synthesize fully amorphous samples by repeated cold-rolling are discussed. In addition, the progress of the solid state amorphization reaction and especially the early stages of phase formation at internal heterophase interfaces are studied systematically. In addition to the analyses of the amorphization mechanism, the present results indicate that repeated cold-rolling is a useful technique to obtain large quantities of amorphous samples over an extended range of glass forming composition. Prozessieren von amorphen und nanokristallinen Materialien fern vom thermodynamischen Gleichgewicht
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Language	English
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Resource Type	Article