Cold-rolling induced amorphization in Cu–Zr, Cu–Ti–Zr and Cu–Ti–Zr–Ni multilayers G.P. Dinda, H. Ro ¨ sner, G. Wilde * Forschungszentrum Karlsruhe, Institute of Nanotechnology, Research Center Karlsruhe, P.O. Box 3640, 76021 Karlsruhe, Germany Available online 20 July 2007 Abstract Amorphous Cu 60 Zr 40 , Cu 55 Ti 35 Zr 10 and Cu 47 Ti 35 Zr 10 Ni 8 alloys were synthesized at ambient temperature by repeated cold rolling with intermediate folding starting from a layered array of individual elemental sheets. A comparison was made of three kinds of glass-forming systems in terms of their glass-forming abilities during solid state processing. The microstructural development during the mechanical alloying process was investigated by X-ray diffraction, scanning and transmission electron microscopy. The progress of solid state reaction in different glass-forming systems was studied in detail at different deformation levels for a better understanding of the early stages of the crystal-to-amorphous transition during intense mechanical deformation. At the beginning of the solid state reac- tion i.e., at low deformation levels, the amorphous phase initially forms at the interlayer interface of the multilayers. The amorphous layer thickness increases with increasing deformation level and in the final stage of rolling, all samples transform almost completely to the amorphous state. The main key to the synthesis of a fully amorphous phase from pure elemental foils is the application of large deformation levels to overexceed the limit of critical solutal supersaturation for amorphization. Ó 2007 Elsevier B.V. All rights reserved. PACS: 81.05.Kf; 81.07.Bc; 81.20.Ev Keywords: Amorphous metals, metallic glasses; Mechanical alloying; Nanocrystals; X-ray diffraction; Glass formation; Microscopy; Scanning electron microscopy; TEM/STEM; Microstructure; Nanocrystals; Surfaces and interfaces; X-rays 1. Introduction Amorphous metallic alloys are thermodynamically metastable with respect to the formation of one or more crystalline phases. It is well known for more than 40 years that amorphous metallic alloys can be obtained by rapid quenching from the melt [1]. Because of the high quenching rate requirements (10 4 –10 6 K/s), only thin ribbons or foils with a thickness less than 100 lm could initially be fabri- cated with rare exceptions such as the Pd- base Pd–Ni–P alloys [2,3]. Several years ago, bulk metallic glasses of La- [4], Zr- [5], and Mg- [6] based alloys have been found with critical cooling rates less than 100 K/s. However, the preparation of bulk metallic glasses by melt quenching is still limited by the appropriate composition and usually contain more than three elements in the vicinity of the deep eutectic point of the phase diagram. On the other hand, glass formation can also be achieved in the solid state through a so-called solid-state amorphiza- tion reaction (SSAR) in both deposited multilayers [7,8] and by mechanical alloying (MA) processes [9–17]. The two main mechanical alloying processes that can induce a crystalline-to-amorphous transformation are milling of powders [9–13] or repeated cold rolling [14–17]. A consid- erable amount of work has been performed on amorphiza- tion induced by mechanical alloying. However, the mechanisms of mechanically induced SSAR are not yet firmly established especially concerning the early stages of the transformation. Compared to ball milling, repeated cold rolling has been much less systematically studied, however, this technique is especially useful to investigate 0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2007.05.147 * Corresponding author. Tel.: +49 7247 82 6414; fax: +49 7247 82 6368. E-mail address: wilde@int.fzk.de (G. Wilde). www.elsevier.com/locate/jnoncrysol Journal of Non-Crystalline Solids 353 (2007) 3777–3781