The goal of the project was the determination and use of the size-dependent phase diagrams of nanostructured metal alloys for the development of nanostructured brazing filler metals with melting point depression. As a model material, the Ag-Cu material system was chosen, being of interest for the main COST action partners. We have studied the effect of the size and shape of the phases (particle, layer) on the thermodynamic properties, the phase equilibria and the shift of the phase transition lines in the binary Ag-Cu system and finally calculated a nano-phase diagram for this system using a modified CALPHAD method [1]. Based on those results a nanostructured Ag-Cu brazing filler metal with a reduced melting temperature for joining of heat-sensitive metals has been developed. A multilayer approach is used for the confinment of the alloy to the nanodimension, in which the thin layers of the Ag-Cu brazing filler metal are alternated with AlN and C diffusion barrier nanolayers [2], [3]. The effect of the Ag-Cu/AlN interface structure on the melting behaviour was studied. With this aim a combined theoretical-experimental approach using HR-TEM investigation and ab-initio DFT calculation was applied to describe the interface structure [2]. A phase separation of the brazing alloy sublayers in the Ag-Cu/AlN multilayers into nanosized grains of Ag and Cu and resulting different structure of local interfaces was observed and described by hybrid Monte Carlo/Molecular Statics simulations [4]. The interfaces between Ag grains and the quasi-single-crystalline AlN sublayers are semi-coherent, whereas the corresponding Cu/AlN interfaces are incoherent [2]. In collaboration with the COST action partner (University of Genova) the melting behaviour of Ag-Cu nanoparticle system was also studied. [1] G.Garzel, J. Janczak-Rusch, L. Zabdyr, Reassessment of Ag-Cu phase diagram for nanosystem including particle size and shape effect, CALPHAD - Computer Coupling of Phase Diagrams and Thermochemistry 36 (2012) 52-56. [2] G.Pigozzi, A.Antusek, J.Janczak-Rusch, M.Parlinska-Wojtan, D. Passerone, C.A. Pignedoli, V. Bissig, J. Patscheider, L.Jeurgens, Phase constitution and interface structure of nano-sized Ag-Cu/AlN multilayers: experiment and ab initio modeling, APL 101, (2012) 181602. [3] J.Janczak-Rusch, G. Pigozzi, B. Lehmert ,M.Parlinska, V. Bissig,W. Tillmann, L. Wojarski, F. Hoffmann, Deposition and utilization of nano-multilayered brazing filler systems designed for melting point depression, Proceedings from the 5th International Brazing and Soldering Conference IBSC 2012: April 22-25, 2012, Las Vegas, Nevada, USA, Eds. R. Gourley and C. Walker,
http://www.asminternational.org, (2012)162-168. [4] S. Brodacka, M. Kozlowski, R. Kozubski, J. Janczak-Rusch, Atomistic simulation of the eutectic mixture in bulk and nano-layered Ag-40at.%Cu, submitted to Modelling and Simulation in Materials Science and Engineering in June 2013.
