Bonding Process And Mechanism Of Ultrasonic-assisted Soldering Of ZrO₂ Ceramic And 1060Al At Low Temperature

ZrO₂ ceramics are expected to become competitive infrared window materials for future hypersonic vehicles due to their excellent physical and chemical properties such as high hardness,good thermal shock resistance,high chemical thermal stability and low high temperature infrared radiation,which can satisfy the demand for mechanical integrity and optical transmission in complex and harsh service environments.The connection of infrared window and aluminum alloy support component is one of the key technologies in the manufacturing for aerospace vehicles,in which a process temperature between 800-1500 ℃ and a long holding time would be required to realize the connection between the ceramic and the metal,but these process temperatures are far above the melting point of the aluminum alloy.The introduction of acoustic energy fields in the soldering process can effectively compensate for the interfacial reaction activation energy and promote the formation of a reliable connection between the solder and the hard-to-wet base material,which can be achieved at a lower process temperature.This work focused on the ultrasonically assisted low-temperature soldering process and mechanism of ZrO₂ ceramics and 1060Al.An ultrasonically assisted brazing method based on a needle-shape acoustic horn was proposed to achieve reliable connections between ZrO₂ceramics and 1060Al by optimizing the process and regulating the interfacial reaction.Subsequently,the relationship between the nano-organizational structure and the macro-mechanical properties of the heterogeneous joint was investigated by first-principle calculations.The dissimilar ZrO₂-Al butt joints were successfully achieved by ultrasonically assisted soldering process using pure Sn filler metal under atmospheric conditions at 250-450 ℃.The influence of process parameters on the microstructure and mechanical properties of the joints were analyzed,while the acoustic dissolution behavior of 1060Al base as well as interfacial reaction mechanism were investigated.The extreme non-equilibrium environment induced by ultrasound greatly promoted the rapid dissolution of the Al substrate into the molten Sn,where the dissolution amount of the Al substrate increased linearly with the ultrasound action time at different ultrasound powers and process temperatures,and the dissolution activation energy of the 1060Al substrate under the acoustic energy field was about 21 k J/mol.Sn-Al alloy formed in situ during the soldering process improved the metallurgical reaction at the ZrO₂/Sn interface,forming a continuous reaction layer of amorphous Al₂O₃ on the nanometer scale at both the ZrO₂/Sn and Al/Sn interfaces.Compared with the ZrO₂/Sn interface,the Al/Sn interface exhibited higher concentrations of Al and O,resulting in a thicker reaction layer,where the Al₂O₃ reaction product layer between the Al matrix and the Sn presented an uneven and rough shape due to the fact that the rate of short-circuit diffusion of Al atoms near the reaction interface was significantly higher than that of bulk diffusion.The highest tensile strength of the ZrO₂/Sn/Al joints was about 30.0 MPa,and the fracture locations almost always occurred on the ZrO₂ ceramic side.The components and structure of the ZrO₂/Sn reaction interface were regulated by adding Ti active elements to pure Sn for the purpose of improving the mechanical properties of the ZrO₂-Al heterogeneous joint.Ultrasonically assisted joining and indirect soldering were employed to realize ZrO₂-Al heterogeneous joints,respectively,and the microstructure,mechanical properties and interfacial reaction mechanism of the joints were analyzed.The Al matrix was dissolved during the ultrasonically assisted process using Sn-Ti alloy solder,accompanied by the generation of a significant amount of diffuse fine Ti Al₃ phases in the weld,while the Ti₆Sn₅ phase in the original brazing material was also significantly refined.A continuous amorphous reaction layer consisting of Ti,Al and O was formed at the ZrO₂/Sn-Ti-Al interface with a thickness of only 5 nm.The maximum tensile strength of the heterogeneous joint was about 38.0 MPa,and the fracture location occurred at the soldering material.There existed a continuous 25 nm thick reaction layer between ZrO₂ and Sn-2Ti at an ultrasonic treatment time of 10 s in the ultrasonic surface metallization process,with the thickness of the reaction layer increasing to 200 nm by extending the ultrasonic action time to 60 s.The ultrasonic action time affected the interfacial reaction significantly,which mainly involved the transformation of Ti O phase structure and the generation of Ti_11.31Sn₃O₁₀ ternary nanophases besides the obvious variation of the reaction layer thickness.The ZrO₂/Sn interface models with the interface products of amorphous Al₂O₃,Ti O,and Ti-Al-O were constructed based on first-principle calculations,in which the bonding properties of the interface were discussed using electron density difference,electronic localization function,interfacial separation work,and partial density of state.The binding strength between ZrO₂ and Sn was mainly influenced by the properties of the ZrO₂/a-MO interface.The charge transfer from ZrO₂ to amorphous Al₂O₃ was about 0.46|e|when pure Sn filler metal was used,where the Al-O distance was about 4.0-4.3?,larger than the internal bond length of amorphous Al₂O₃,leading to the formation of a weaker interfacial bond.O preferentially bonded with Ti at the ZrO₂/a-Ti Al O₂ interface and bound stronger to Ti than to Al.While there was a 0.05|e|charge transfer between ZrO₂and Ti O at the ZrO₂/a-Ti O interface,with a strong density-of-state hybridization between Ti-O.The maximum separation work at the ZrO₂/Sn,ZrO₂/a-Al₂O₃,ZrO₂/a-Ti Al O₂,and ZrO₂/a-Ti O interfaces were 0.07 J/m²,0.08 J/m²,0.09 J/m²,and 0.13 J/m²,respectively,which explained the enhanced effect of Ti and Al elements on the mechanical properties of ZrO₂-Al joints,and the improvement of Ti was more obvious.