Research On Wetting And Brazing Of Alumina By SnAgCu-Ti Active Solder

Active brazing is a promising method to manufacture alumina components with complex geometry.The wettability of active Sn0.3Ag0.7Cu-Ti?SAC-Ti?solder was studied in this paper.The influence of Ti fraction,temperature and crystal orientation of base material on wettability was studied.The mechanism of enhanced wetting by active element Ti was studied.Additionally,the adverse impact of Ti-Sn intermetallic compound on wetting was analyzed by thermodynamic analysis and modeling.Reliable alumina/alumina joints were obtained by direct brazing using Sn0.3Ag0.7Cu-Ti.The influence of Ti fraction and brazing temperature on joint microstructure and mechanical property were studiedSn0.3Ag0.7Cu-x%Ti?wt.%x=0.3,0.7,1,2,3,4?filler alloy were prepared by ball milling.No metallurgical reaction took place in the process.The addition of Ti had no influence on the melting temperature of the solder.Sessile drop experiments were conducted to study the wettability of Sn0.3Ag0.7Cu-Ti on alumina.Results indicate that the addition of Ti had a significant influence on wetting.Alumina is completely unwetted by SAC,with contact angle unchanged at 148°.With the addition of Ti,the droplet started to spread.Equilibrium contact decreased and spreading rate increased with rising Ti fraction.The wetting was inhibited in high Ti containing droplets because of the intense formation of Ti-Sn intermetallic compounds,with droplet shape changing from spherical to conical.Improved sessile drop method was used to investigate the kinetics of spreading process.Spreading accelerates as Ti content rises.However,spreading slows down when Ti content riches 1%owing to lower Ti activity.Temperature could significantly influence the wettability of Sn0.3Ag0.7Cu-Ti.Contact angle of droplet continued decreasing from melting to 1050°C.In the range of625°C-850°C,850°C-1000°C and 1000°C-1050°C,enhanced wetting was controlled by interfacial reaction,decreasing surface tension and vaporization of liquid solder,respectively.In low Ti containing droplets,equilibrium contact angle was not influenced by temperature.However,in SAC-3Ti and SAC-4Ti,wettability of solder was improved because of lower viscosity.The wetting and spreading of SAC-Ti droplets on alumina was controlled by reaction.Ti atoms accumulated on liquid/alumina interface under the driving force of minimizing surface tension.Subsequent reaction with O decomposed from alumina promoted wettability.The adverse impact of Ti-Sn formation on wetting is critical.In the idealized circumstance where Ti-Sn reaction would not take place,the value of cos?changes linearly with initial Ti fraction.Experimentally,cos?lags behind theoretical line in high Ti containing droplets.The gap between theory and experiments widens with increasing Ti fraction.Direct brazing of alumina to alumina using SAC-Ti was conducted in a vacuum.?-Sn,Cu₆Sn₅ and Ti₆Sn₅ were found in brazing seam.Ti fraction had a great influence on joint microstructure and mechanical property.Brazing seam could not be completely filled with SAC-0.7Ti in 1000°C because of poor wettability.Crack could be seen on the interface.The filling property of solder was improved in SAC-1Ti and SAC-2Ti.However,pores of incomplete filling was observed in SAC-3Ti and SAC-4Ti because of poor wettability.Brazing temperature also had effects on joint microstructure and mechanical property.The viscosity of SAC-3Ti and SAC-4Ti decreased with rising temperature.The number of pores decreased and the mechanical property improved.Orientation of base material had no significant influence of wetting,joint microstructure or joint property.However,it had a great effect on the morphology and distribution of reaction product.The shape of reaction product is trapezoidal and island-like on A and M oriented sapphire.The shape of reaction product is triangular in C and R sapphire.The?220?face of TiO grows on the?006?face of alumina.