Phase formation and reaction kinetics in the system Ti-Sn

The system Ti-Sn was investigated with regard to the phases forming in the Sn-rich region and the reaction between titanium and liquid tin. Phase equilibria were studied by isothermal annealing of powder and melted alloy samples in the range of 29 to 88 at.% Sn and 350 degrees C to 1100 degrees C. Phase compositions were determined using XRD, SEM and EDX methods. The reaction kinetics between solid Ti and liquid Sn were investigated using both thin film and bulk diffusion couples. Surface contamination, presumably oxide layers, initially inhibits any reaction between bulk Ti and Sn. Reaction layers after isothermal annealing of the diffusion couples were analyzed with optical microscopy, SEM/EDX, and XRD. The experiments show that in this system a new intermetallic phase TiSnx with a composition of about 60 at.% Sn exists, which is stable up to about 750 degrees C. This phase is evidently the fastest forming intermetallic if Liquid Sn is reacting with Ti or Ti-rich phases. Thus it is dominating in annealed powder and alloy samples as well as in bulk and thin film diffusion couples. However, during solidification from Sn-rich melts another phase, Ti6Sn5 is dominating. A revised phase diagram of the Ti-Sn system is presented, incorporating the TiSnx phase. Since the formation of TiSn, is slow and the thermal stability of TiSn, is not as high as expected for the more Ti-rich phases the system Ti-Sn is not suitable for Transient Liquid Phase (TLP)-bonding.