Atomistic simulation of the eutectic mixture in bulk and nano-layered Ag–40 at.%Cu alloy S. Brodacka a,⇑ , M. Kozlowski a , R. Kozubski a , J. Janczak-Rusch b a M. Smoluchowski Institute of Physics, Jagiellonian University in Krakow, Reymonta 4, 30-059 Kraków, Poland b EMPA – Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland article info Article history: Received 1 November 2013 Received in revised form 24 February 2014 Accepted 12 March 2014 Available online 14 April 2014 Keywords: Silver–copper alloy Eutectic decomposition Phase separation Monte Carlo Hybrid simulations abstract Eutectic decomposition in bulk Ag–40 at.%Cu and its nanolayers with (0 0 1) free surfaces was simulated in an atomistic scale by means of hybrid Monte Carlo/Molecular Statics simulations with Tight-Binding Second Moment Approximation type potentials. While lamellar Cu precipitates formed in the bulk, diver- sified precipitate morphology and surface segregation of Ag atoms was observed in the layers. The effect of the layer thickness on the precipitate geometry was analysed. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction 1.1. Aim of the study The eutectic Ag–40 at.%Cu alloy (melting at the eutectic temper- ature of 1053 K/778 °C) is a common brazing material widely used in brazing stainless steels, copper and nickel based alloys, as well as the shape memory alloys. The joining technology (e.g. brazing, soldering, mechanical fastening) of materials becomes nowadays especially challenging due to the general tendency for device min- iaturization. One of the important tasks in this area is a possibility for lowering the brazing or soldering temperature by the decreas- ing of melting temperatures of brazing or soldering materials [1].A number of recent achievements in this field have been connected with an application of nanostructured brazing fillers: while Ag 2 CO 3 metallo-organic nanoparticles successfully substitute the high- temperature solders Pb–10Sn and Pb–5Sn withdrawn from use in the electronics because of worldwide environmental preservation, the Au nanoparticles are used in bonding Si chips, where Pb-rich high-temperature solders were applied, in the past. In many indus- trial applications where lowering the melting point of brazing metal filler alloys is especially important multi-nano-layered structures appear more suitable than nanoparticles. Although the phenomenon of the ‘‘melting point depression’’ (MPD) in nano-layered brazing fillers has been observed experimentally [2] and its phenomenological thermodynamic explanation was attempted [3,4] the atomistic background of the effect has been still unknown. Experimentally, it has been found out that the MPD effect occurs in specifically designed ‘‘sandwich’’ structures composed of nanolayers of the brazing filler separated by so called ‘‘diffusion barriers’’ (DB) – i.e. nanolayers of a non/low-reactive material, which deteriorate during the brazing process. It is supposed that the MPD phenomenon stems from the specific features of filler/DB interphases. Elucidation of the MPD phenomenon occur- ring in the eutectic Ag–Cu/DB multi-nano-layers by means of atomistic simulations is the goal of the investigation, whose first stage was the atomistic modelling of the eutectic microstructure formed in the Ag–Cu nanolayers. The results reported in the pres- ent paper are a starting point for the study of the equilibrium atomic configuration of Ag–40 at.%Cu/DB interfaces. 1.2. State of the art The Ag–Cu binary system is a typical eutectic one with the eutectic point corresponding to 40 at.%Cu at T ¼ 1053 K (Fig. 1a) [5]. Both pure Ag and Cu crystallise in face-centered cubic struc- tures with, however, considerably different lattice constants: 0.409 nm for Ag and 0.361 nm for Cu [6]. Due to this huge lattice mismatch the bulk eutectic mixture shows a characteristic lamellar microstructure (Fig. 1b) [7]. http://dx.doi.org/10.1016/j.commatsci.2014.03.021 0927-0256/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +48 126635716. E-mail address: sylwia.brodacka@uj.edu.pl (S. Brodacka). Computational Materials Science 89 (2014) 30–35 Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci