- - - Basic Y. Plevachuk et al.: Determination of liquidus temperature in Sn-Ti-Zr alloys by viscosity, electrical conductivity Yuriy Plevachuka, Stepan Mudrya, Vasyl Sklyarchuka, Andriy Yakymovycha, Andriy Korolyshyna, Ihor Shtablavyya, Yuriy Kulyka, Ulrich E. Klotzc, Chunlei ~ iu~?~, Christian Leinenbachb "Ivan Franko National University, Department of Metal Physics, Lviv, Ukraine '~m~a, Swiss Federal Laboratories for Materials Testing and Research, Laboratory of Joining & Interface Technology, Dubendorf, Switzerland 'FEM, Research Institute Precious Metals & Metals Chemistly, Schwabisch Gmund, Germany d ~ o ~ at: ABB Research Center, Baden-Dattwil, Switzerland Determination of liquidus temperature in Sn - Ti - Zr alloys by viscosity, electrical conductivity and XRD measurements based active brazing filler metals. Experimental results on this system, however, are rather scarce. The diagram is rather uncertain regarding most of the liquidus, especially on the Sn rich side. In this work, the atomic structure and temperature dependence of structure-sensitive physical properties (dynamic viscosity and electrical conductivitv) of liquid Sn-Ti-Zr alloys in the Sn-rich corner were i EMPP tigated in a wide temperature range with special attention to the melting-solidification region. The results allowed the liquidus line position to be specified. Keywords: Sn-Ti-Zr; Phase diagrams; Viscosity; Elec- trical conductivity; XRD on structure-sensitive properties of these systems in the liq- uid state are scarce in the literature. The determination of the liquidus temperature by differen- tial thermal analysis (DTA) methods is often very compli- cated and can lead to substantial errors. At this point, investi- gations by other methods, supplementing each other, enables this determination to a high& degree of consistency. R-r-ntly the electrical conductivity and viscosity investi- r200901 - 38 >fsome binary Sn-Ti, Sn-Zr and ternary Sn-Ti- Zr liquid alloys were reported [6,7]. In this work, viscosity, electrical conductivity and X-ray measurements were car- ried out for liquid Sn-Ti-Zr alloys on the Sn-rich side over a wide temperature range above the liquidus. Special atten- tion was given to the melting-solidification region. 2. Materials and methods 1. Introduction 2.1. Materials Filler metals for diamond brazing are usually based on tern- ary or quaternary Cu- and Sn-based systems such as Cu- Sn-Ti-Zr which contain active elements such as Ti or Zr in order to wet the diamond or other ceramic materials. Very accurate information on physical properties, thermo- dynamic data and phase diagrams of all the binary and tern- ary Cu- and Sn-based subsystems is crucial for the brazing processes. Thermodynamic properties of binary Sn-Ti and Sn-Zr systems are comparatively fully studied [I-51, but discrepancies between the published assessments still remain, and some aspects are undetermined. In particular the intervals of solubility at higher temperatures, the struc- ture of intermetallic compounds and their thermal expan- sion, especially near the liquidus line on the Sn rich side of these systems have scarcely been studied. The components of the Sn-Ti, Sn-Zr and Sn-Ti-Zr systems show substantial differences in their melting tem- peratures. Therefore, the addition of a refractory element effects a drastic increase in the liquidus line, and even a negligible error in the alloy composition can provoke a seri- ous error in determining the onset of solidification. Because of this peculiarity and the experimental difficulties, the data A number of ternary Sn-Ti-Zr alloys covering the Sn-rich comer of the phase diagram and providing the most exhaus- tive information were selected for the studies. The sample compositions are listed in Table 1. The samples were pre- pared in an arc melting furnace in a purified argon atmo- sphere. Ingots of tin, titanium and zirconium, all of them with a purity of 99.99 %, were cleaned of oxide films, then mixed and installed in the chamber of the furnace. In order to achieve good homogeneity, the alloys were remelted 5 times. 2.2. Viscosity The measurements of the dynamic viscosity were carried out using a computer-controlled oscillating-cup viscometer [8]. Cylindrical boron nitride crucibles were used. The tem- perature was measured with a WRe-5/20 thermocouple arranged just below the crucible. The experiments were performed in an atmosphere of Ar+ H2 after initially pumping out the working volume of the furnace to about 10 Pa. A homogeneous temperature field was created inside Int. J. Mat. Res. (formerly Z. Metallkd.) 100 (2009) 5 689 EMPA20090138 EMPA20090128