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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°, 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.