Research On Ultrasonic Assisted Brazing Joining Technology Of Si₃N₄ Ceramic And Titanium Alloy

The application of ultrasonic vibration in the metal melt can effectively improve the solidification structure and properties.The ultrasonic probe with high-temperature erosion resistance is a necessary condition to ensure the long-term stable introduction of ultrasonic waves into the melt.The TC4 alloy horn on the ultrasonic probe and the Si₃N₄ceramic tool rods are usually connected by threaded screw rods.The connection is subjected to ultrasonic vibration and high temperature at the same time during operation,which is prone to loosening and causes ceramic tool rods to break,which in turn makes it difficult for ultrasonic equipment to work continuously.In order to solve this problem,this paper studies the brazing connection process between Si₃N₄ ceramics and titanium alloys and applies ultrasonic vibration to the surface of the brazed base metal during pre-dipping and brazing.Influence law on the microstructure and properties of coatings and brazed joints.The main conclusions of this paper are as follows:1.The research on the ultrasonic pre-dipping process of the Si₃N₄ceramic surface was carried out,and a layer of aluminum-silicon alloy brazing filler metal was prepared on the surface of the Si₃N₄ ceramic base material.From the test results,it is found that there are defects such as shrinkage holes at the interface between the pure aluminum coating and the Si₃N₄ ceramic.Defects such as pores at the interface are reduced;when the Si content increases to 12wt.%,the interface between the coating and the Si₃N₄ ceramic is smooth and dense;with the increase of the ultrasonic vibration time,the thickness of the coating increases,and the internal and The defects at the interface decreased;with the increase of ultrasonic amplitude,the Ti（Al,Si）₃ intermetallic compounds in the coating increased,and the defects such as shrinkage holes in the coating decreased;The reasonable process conditions for ultrasonic pre-dipping of Si₃N₄ ceramic surface ceramics are obtained:ultrasonic amplitude is 7μm,ultrasonic action time is 8s.2.Based on pre-dipping Al-12Si on the surface of the base metal,the conventional brazing connection process of Si₃N₄ ceramics and TC4 alloy was studied.It is found that the interface structure of the joint obtained under the conditions of brazing temperature 760℃and holding time 30s is Si₃N₄/Al/Ti（Al,Si）₃/Ti Al/Ti-6Al-4V;With the increase of time,the reaction layer at the interface between TC4 alloy and brazing filler metal gradually thickened,and the shear strength of the joint first increased and then decreased.The temperature is 760℃and the holding time is in the 30s.Under this process condition,the shear strength of the joint can reach66.08MPa;the fracture of the joint mainly occurs in the middle of the solder,and there are many dimples on the fracture surface,which is a ductile fracture.3.Using the Al-12Si alloy coating on the surface of the base metal on both sides as the brazing filler metal,the ultrasonic-assisted brazing connection process of Si₃N₄ ceramics and TC4 alloy in an atmospheric environment was studied.The test results show that the interface structure of the joint is Si₃N₄/Al/Ti（Al,Si）₃/Ti-6Al-4V under the conditions of brazing temperature of 760℃,holding time of the 30s,ultrasonic amplitude of 4μm and ultrasonic action time of 8s;With the increase of ultrasonic action time,the thickness of the intermediate brazing filler metal layer decreases,the thickness of the reaction layer at the brazing filler metal layer/TC4 alloy base metal interface increases,and the shear strength of the joint increases;The ideal process conditions for ultrasonic-assisted brazing of Si₃N₄ ceramics and TC4 alloys were obtained:brazing temperature 760℃,holding time 30s,ultrasonic amplitude 4μm,ultrasonic action time 8s,under these process conditions,the shear strength of the joint under this process condition is about 113.20MPa,which is about 71.3%higher than that of the joint under conventional brazing.