Structure of rapidly quenched (Cu 0.5 Zr 0.5 ) 100x Ag x alloys (x = 0–40 at.%) N. Mattern a,⇑ , J.H. Han a , K.G. Pradeep b , K.C. Kim c , E.M. Park a , D.H. Kim c , Y. Yokoyama d , D. Raabe b , J. Eckert a,e a IFW Dresden, Institute for Complex Materials, Helmholtzstr. 20, 01069 Dresden, Germany b Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany c Center for Non-crystalline Materials, Yonsei University, 134 Shinchon-dong, Seodaemun-ku, Seoul 120-749, Republic of Korea d Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan e TU Dresden, Institute of Materials Science, Helmholtzstr. 7, 01069 Dresden, Germany article info Article history: Received 13 March 2014 Received in revised form 4 April 2014 Accepted 7 April 2014 Available online 18 April 2014 Keywords: Metallic glass Phase separation Atom Probe Tomography Ag–Cu–Zr abstract The influence of Ag addition on the microstructure of rapidly quenched (Cu 0.5 Zr 0.5 ) 100x Ag x melts was investigated (x = 0–40 at.%). Fully glassy alloys were obtained for 0 6 x 6 20 at.% Ag, which are character- ized by a homogeneous microstructure without any indication of phase separation. For 30 6 x 6 40 at.% Ag a composite structure is formed consisting of fcc-Ag nano-crystallites 5 nm in size and an amorphous matrix phase Cu 40 Zr 40 Ag 20 . With higher Ag-content the volume fraction of the fcc-Ag phase becomes increased mainly due to crytal growth during quenching. The primary formation of fcc-Ag for 30 6 x 6 40 at.% Ag is confirmed by the analysis of the microstructure of mold cast bulk samples which were fully crystalline. From the experimental results we conclude that the miscibility gap of the liquid phase of the ternary Ag–Cu–Zr system may occur only for x > 40 at.% Ag. For the bulk glass forming qua- ternary Cu 40 Zr 40 Al 10 Ag 10 alloy a homogeneous element distribution is observed in accordance with the microstructure of ternary (Cu 0.5 Zr 0.5 ) 100x Ag x glasses (x = 10, 20 at.%). Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Bulk metallic glasses (BMGs) exhibit excellent mechanical prop- erties such as high strength and large elastic strain, making them attractive for structural applications [1]. Among them, Cu–Zr based BMGs demonstrate a high potential of having industrial applica- tions in the future owing to their high strength, hardness, wear resistance, casting ability and high glass-forming ability. Recently, Cu–Zr–Al–Ag bulk glass forming alloys were developed with a crit- ical diameter up to 25 mm for copper mould casting [2–4]. Bulk glass formation was also observed for ternary Cu–Zr–Ag alloys with a critical diameter up to 6 mm for Cu 45 Zr 45 Ag 10 [5,6]. For some Cu–Zr–Al–Ag BMGs also extended plasticity in compression and even in bending was reported [2,7]. However, the structural reason behind the deformability is not known so far. The presence of nanometer-scale phase separation was detected for a Cu 43 Zr 43 A 7 Ag 7 BMG (2 mm in thickness) by Atom Probe Tomography (APT) and was related to the extended plasticity [8]. Possible phase separation of submicron-scale upon annealing is discussed for glassy Cu 35 Zr 45 Ag 20 by a systematic study of the devitrification and glass-forming ability of rapidly quenched Cu–Zr–Ag alloys [9]. The same group has also reported the occurrence of possible phase separation for a Zr 48 Cu 36 Al 8 Ag 8 BMG (3 mm in thickness) in the supercooled liquid state just prior to crystallization [10]. On the other side, for a Zr 53.8 Cu 31.6 Ag 7.0 Al 7.6 BMG (2 mm in thick- ness) with large bending and compressive plastic strain, the pres- ence of heterogeneities was ruled out through Transmission Electron Microscopy (TEM), APT and anomalous small-angle X- ray scattering investigations [7]. Heterogeneities on the atomic scale in liquid and glassy Cu 45 Zr 45 Ag 10 were concluded from molecular dynamics simulations [11]. The model structure consists of Zr-rich clusters centred by paired and stringed Ag atoms and Cu- rich icosahedra centred by Cu, which give rise to slow-dynamics regions and improved glass-forming ability due to the Ag addition [12]. From thermodynamics point of view, Ag and Cu have positive enthalpy of mixing (DHmix = +2 kJ/mole) and as consequence a miscibility gap exists in the metastable undercooled liquid of the binary Ag–Cu system. According to the thermodynamic assess- ments of the ternary Ag–Cu–Zr phase diagram [13,14], an extended miscibility gap exists in the equilibrium liquid. Fig. 1 shows a cal- culated section of the Ag–Cu–Zr phase diagram along (Cu 0.5- Zr 0.5 ) 100x Ag x using the data given in [13]. A stable miscibility gap of the liquid occurs in the range from about x = 35 at.% Ag to http://dx.doi.org/10.1016/j.jallcom.2014.04.047 0925-8388/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +49 3514659367. E-mail address: n.mattern@ifw-dresden.de (N. Mattern). Journal of Alloys and Compounds 607 (2014) 285–290 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom