Wettability And Brazing Interface Reactivity Of Tin-based Active Metals On Zirconia Ceramic Surfaces

Zirconia,as an important component of engineering ceramics,have demonstrated excellent performance in many aspects and play important roles in machining,aerospace,fuel systems,biotechnology,electronics,and other fields,which are difficult to replace.Due to the deepening industrial demand and the increasingly complex industrial application environment,a single material faces severe challenges.Therefore,the connection of dissimilar materials has been proposed to break this situation.For ceramics,brazing is one of the best methods for connecting dissimilar materials,whether in terms of economy or stability.However,brazing inevitably involves the wetting problem between the solder and the substrate.Tin-based solder alloy,as a typical low-melting-point solder alloy,has been widely used in biotechnology,electronics,and other fields.However,it is difficult to wet on the surface of zirconia,which limits the application of zirconia ceramics in corresponding fields.Moreover,with the current industrial transformation focusing on biomedicine and electronics,the above contradictions become more prominent.Therefore,improving the wettability of tin-based solder alloy on the surface of zirconia,revealing its wetting mechanism and spreading kinetics,and proposing effective brazing schemes based on these findings are of great significance for the industrial application of zirconia.This paper investigates the wettability of Sn-8Zr,Sn-8Ti,and Sn-4Zr-4Ti solder alloy on YSZ and YSZ_2-x substrates using both traditional sessile drop method and modified sessile drop method.The interface microstructure,wetting mechanism,interfacial thermodynamics,and spreading kinetics of the above solder alloy on the surface of zirconia ceramics were thoroughly investigated after wetting.Furthermore,brazing interface reactivity of the solder alloy corresponding to good wettability was studied.The following important conclusions were obtained from this study:（1）The wettability of Sn-8Ti/YSZ,Sn-8Zr/YSZ,and Sn-4Zr-4Ti/YSZ systems was significantly improved by the addition of Zr and/or Ti at 800-900℃.In systems with Zr additives,the final wettability depends on the adsorption of Zr and the formation of ZrO_2-x,where adsorption is the dominant factor.In addition,the competition between adsorption and reaction leads to the anomalous dependence of contact angle on temperature in Zr-containing systems.The improved wettability of the Sn-8Ti/YSZ system is mainly attributed to the formation of Ti₂O₃ and Ti_11.31Sn₃O₁₀at the interface.In the Sn-4Zr-4Ti/YSZ system,ZrO_2-x is the preferential precipitating phase,and wettability exhibits an adsorption-dominated characteristic.The synergistic adsorption effect of the two active additives leads to the optimal wettability（～30°）in this study.For Sn-8Zr/YSZ and Sn-4Zr-4Ti/YSZ,the spreading kinetics are primarily controlled by the dissolution of Zr in Zr-containing additives,followed by the formation of wetting ridges.The spreading kinetics of Sn-8Ti/YSZ are limited by the reaction kinetics of Ti₂O₃ and Ti_11.31Sn₃O₁₀ precipitated at the solid-liquid interface,and the significant adsorption at the interface reduces the energy barrier for wetting.（2）In the Sn-8Ti/YSZ_2-x,Sn-8Zr/YSZ_2-x,and Sn-4Zr-4Ti/YSZ_2-x systems at temperatures between 800-900℃,the wettability of tin-based alloys with active elements on YSZ_2-x is strongly correlated with temperature.The final contact angle of the Sn-4Zr-4Ti/YSZ_2-x and Sn-8Ti/YSZ_2-x systems decreases with increasing temperature.In the former,the precipitation of the Sn₂Zr intermetallic compound enhances the metallic property of the interface and strengthens the adsorption of the active elements Zr and Ti.In the latter,the addition of Ti suppresses the decomposition of YSZ_2-x（maintaining the original metallic property）and enhances the adsorption at the solid-liquid interface,resulting in the final wettability.The Sn-8Zr/YSZ_2-xsystem exhibits an abnormally temperature-dependent wettability due to the competing relationships between Zr adsorption,YSZ_2-y reaction product formation,and supersaturated precipitation of Sn₂Zr intermetallic compounds.The application of scaling laws to spreading kinetics analysis indicates that the spreading of the system is not affected by convection resulting from substrate decomposition.The wettability activation energies of the Sn-4Zr-4Ti/YSZ_2-x and Sn-8Ti/YSZ_2-x systems are 197kJ/mol and 243 kJ/mol,respectively,corresponding to the chemical bond energies of Sn-Zr and Ti-Zr at the liquid-solid interface during the formation process.（3）In the brazing experiment of YSZ|Sn-Zr-Ti|YSZ_2-x at 850℃,the interface microstructure of the YSZ|Zr|Sn|Ti|YSZ_2-x joint is consistent with that of the Sn-4Zr-4Ti/YSZ wetting system.A continuous ZrO_2-x reaction layer with a thickness of 2.14μm is mainly formed at the interface.However,on the YSZ_2-x|Ti|Sn side,substrate dissolution and YSZ_2-y re-precipitation occur,which is different from the Sn-4Zr-4Ti/YSZ_2-x wetting system where no Sn₂Zr intermetallic compound is precipitated at the solid-liquid interface.This is mainly due to the consumption of Zr by the reaction layer on the YSZ side,which inhibits the precipitation of Sn-Zr intermetallic compound.In the YSZ|Ti|Sn|Zr|YSZ_2-x joint,the interface structure of the YSZ|Ti|Sn side cannot be related to its corresponding wetting system.Instead,a continuous Ti₂O₃ thin film reaction layer is formed at the solid-liquid interface,which is likely due to the concentration gradient caused by magnetron sputtering.The interface structure of the YSZ_2-x|Zr|Sn side of the joint is consistent with that of the Sn-4Zr-4Ti/YSZ_2-x wetting system,mainly including substrate dissolution,YSZ_2-y re-precipitation,and concentrated precipitation of Sn₂Zr intermetallic compound near the etched pit.However,the precipitation of Sn₂Zr intermetallic compound at the interface may weaken the joint performance.