Phase formation and reaction kinetics in the vanadium-tin system

The V-Sn system was investigated with regard to the phase formation in the Sn-rich region and the reaction between vanadium and liquid tin. Phase equilibria were studied by isothermal heating of powder alloy samples in the temperature range 200-600degreesC for compositions 60-80 at.% Sn up to 680 h. Phase identification was done using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) methods. High-temperature XRD up to 800degreesC was used to determine the stability range Of V2Sn3. A thermodynamic modeling of the V-Sn system was done and the phase diagram was calculated. The reaction kinetics between solid V and liquid Sn was investigated using differently prepared bulk diffusion couples heated at 450 - 600degreesC for up to 100 h. Reaction layers after isothermal heating of diffusion couples were analysed with SEM/ EDX and XRD. The fastest forming intermetallic phase if the liquid alloy is reacting with V is V2Sn3 and it is the predominant phase in tempered powder and bulk diffusion couples. The "V3Sn" phase is virtually not formed under these conditions. However, V2Sn3 phase formation is too slow for practical applications in transient liquid-phase bonding.