Wettability and Spreading Behavior of Sn-Ti Alloys on Si3N4

The purpose of this study was to investigate the wetting behavior and interfacial reactions of Sn-Ti alloys, which has been widely applied to join ceramics with metals, on Si3N4 substrates. The isothermal wetting process of Sn-xTi alloys (x = 0.5, 1.0, 1.5, 2.0 and 2.5 wt.%) on Si3N4 was systematically studied from 1223 K to 1273 K through sessile drop methods. The microstructures of the interface were characterized by X-ray diffraction (XRD) and microscope (SEM). The active Ti element remarkably enhanced the wettability of Sn-xTi melts on Si3N4 substrates because of the formation of metallic reaction layers (Ti5Si3 and TiN). With the Ti content rising, thicker Ti5Si3 layer formed on the TiN phase inducing a lower equilibrium contact angle. The value of the lowest contact angle was 6 degrees, which was obtained in the Sn-2.0Ti/Si3N4 system at 1273 K. Larger Ti5Si3 grains were found in Sn-2.5Ti melt and a higher final contact angle was obtained. Lower temperature increased the final contact angle and slowed down the spreading rate. The formation of reaction products was calculated thematically, and the spreading kinetics was calculated according to the reaction-driven theory. The spreading behavior of Sn-Ti alloy on Si3N4 ceramic was composed of rapid-spreading stage and sluggish-spreading stage. The calculated activity energy of spreading was 395 kJ/mol. Eventually, the wetting process of Sn-2.0Ti/Si3N4 system was successfully elucidated. These results provide significant guidance information for the brazing between metals and Si3N4 ceramic.