Experimental study and thermodynamic calculation of Au-Bi-Sb system phase equilibria Dragan Manasijević 1,a , Duško Minić 2 , Dragana Živković 1 , Živan Živković 1 1 University of Belgrade, Technical Faculty, VJ 12, 19210 Bor, Serbia 2 University of Pristina, Faculty of Technical Sciences, 38220 Kosovska Mitrovica, Serbia a e-mail: dmanasijevic@tf.bor.ac.yu Keywords: Au-Bi-Sb system; phase diagram; DTA; EDX Abstract. Phase equilibria in the Au–Bi–Sb ternary system have been studied experimentally and calculated by the CALPHAD method. Three calculated isopleths from each element corner with equal molar ratio of the other two elements were compared with the DTA results from this work. Three ternary invariant reactions were noted. Calculated isothermal sections in the temperature range of 200- 400°C were presented. Calculated phase diagram of isothermal section at 300°C was compared with the results of SEM/EDX analysis. Reasonable agreement between calculations and experimental data was observed in all cases. Introduction The lead-tin alloy systems have been the most commonly used soldering materials in electronic interconnection and packaging because of their low cost and unique combination of physical, chemical, mechanical properties, manufacturability and reliability. However, because of environmental and health concerns, the intensive search for alternative solder alloys is in progress. Thermodynamic modelling of phase equilibria in perspective systems represents first necessary step for development of new lead-free soldering materials. For this purpose, in the frame of COST 531 action [1] and SGTE (Scientific Group Thermodata Europe), thermodynamic database based on recent version 4.4 SGTE [2] values of Gibbs energies for a pure element was developed [3]. It contains the data for carefully tested binary phase diagrams, suitable for prediction of phase equilibrium in multicomponent systems. Knowledge of the phase equilibria in the Au-Bi-Sb ternary system is desirable for the development of lead-free solder alloys. There are only two references concerning phase equilibria of this ternary system. Gather [4] studied an isothermal section of the Au–Bi–Sb ternary system at 493 K. Paul et al. [5] studied diffusion properties of Au2Bi and AuSb2 intermetallics at 230 and 330°C by the diffusion couple method. In this paper, the Au-Bi-Sb ternary system is investigated via experiment and thermodynamic binary-based prediction according to CALPHAD technique [6- 8]. Calculated sections were compared with DTA and SEM/EDX results from the present study. Experimental procedure All samples were prepared from metals of 99.99 wt.% purity. Weighted amounts of metals were melted and annealed in evacuated and sealed quartz capsules at 300°C for 200 hours. After annealing, samples prepared for DTA measurements were gradually cooled down in order to obtain desired equilibrium at room temperature. Samples prepared for SEM-EDX investigation were quenched into ice water from 300°C. DTA measurements were carried out with the Derivatograph ( MOM Budapest ) apparatus with Pt/Pt10%Rh thermocouples under following conditions: argon atmosphere, heating rate 5 K/min and sintered Al 2 O 3 as the reference specimen. The equilibrium compositions in quenched samples were determined using JEOL scanning electron microscope with accelerating voltage 20kV and EDX analyzer.