Study On Metal-Ceramic Welding Mechanism And Interface Mechanical Behavior

The application of the metal-ceramic connection has expanded from the original electronic field to the thermal barrier coatings of today's aircraft engines.The working environment of the thermal barrier coating may be affected by external impacts,in addition to high-speed rotation and high temperatures.Therefore,it is necessary to study the dynamic mechanical behavior and failure mechanism of metal-ceramic joints.In recent years,researchers have proposed a variety of methods to realize metal-ceramic connections.The research focuses mainly on the connection of process parameters.Researchers has pay more attention to the mechanical behavior of metal-ceramic connection when the connection has be exposed to extreme environments,but there are few studies on mechanical properties,especially dynamic mechanical properties and failure mechanisms.Besides,the weakest of the metal-ceramic joint is generally located at the interface,it is particularly important to explain the mechanical behavior and failure mechanism of the metal-ceramic joint interface at different strain rates.The main purpose of this paper is to explain the effect of microstructure and strain rate on the mechanical behavior and deformation mechanisms of metal-ceramic interface.Firstly,the failure strength and strain of metal-ceramic interface is pretty low,new dynamic loading equipment is designed to fit the charaction of ceramic-metal interface;Secondly,explain the connection mechanism of the interface;At last,the flexural/shear strength at different strain rates is tested and explain failure mechanism and mechanical behavior.The results and important conclusions obtained are briefly summarized as follows:(1)As the metal-ceramic interface has low failure strength and strain,there is a problem that the collected signal is weak and difficult to identify when using the traditional Hopkinson bar.Improvements have been made to the traditional bar,and hollow aluminum alloy tubes have been designed.Compared to the traditional ones,the improved experimental device can amplify the signal nine times,which ensures the reliability of the test and validity of the collected data.The improved test solves the difficulties of experimental issue.(2)In order to get the theory of metal-ceramic connection,in the preparation process,the metallization of the A95 aluminum ceramic was successfully achieved by adding a glass phase in the traditional Mo-Mn method.The AgCu28 solder was used to weld the ceramic and Kovar.SEM and EDS were used to characterize and analyze the microstructure.Studies have shown that the connection between metal and solder is achieved through diffusion and intercrystalline penetration;the solder and the metallization of the nickel plate are connected by diffusion;the metallization and ceramic are connected through the mutual migration of the glass phase.(3)In order to investigate the mechanical behavior and failure mechanism of the metal-ceramic interface,the four-point bending test method was designed to replace the three-point bending test method,as three-point method could not accurately test the bending performance.Use DIC to verify the effectiveness of the improved test method.The test and analysis results show that the static/dynamic flexural properties of the metal-ceramic interface are approximately 150 MPa and 115 MPa,respectively.Microscopic analysis of the fracture revealed that the crack originated in the ceramic and then expanded into the metallized band until the sample failed.Under static conditions,the damage of the metal-ceramic interface is mainly caused by the intergranular/transgranular cracking of the ceramic,while the failure of the ceramic under dynamic conditions is mainly due to intergranularity.In addition,as the strain rate increases,more holes appear in the ceramic on the fracture,which also results in the lower dynamic bending strength of the metal-ceramic interface than the static bending strength.(4)The conventional shear tests have incalculable bending moments and difficult to obtain accurate test data,new test methods have been designed.The shear strength of the metal-ceramic interface was tested using an antisymmetric four-point bending loading method.This method can not only greatly reduce the influence of bending moment on shearing,but also can estimate the influence of bending moment on shearing through DIC large technology.The results show that the static/dynamic shear properties of the metal-ceramic interface are approximately 38 MPa and 40 MPa,respectively.Microscopic analysis of fractures revealed that the fracture paths propagated from the solder to the ceramic and resulted in eventual failure.The biggest difference between static and dynamic fractures is the discovery of ceramic adiabatic shear bands at dynamic fractures.Based on the formulae of strain energy and thermodynamics,the adiabatic temperature rise of the ceramic in the loading process has exceeded the melting point of the ceramic through theoretical calculations.The melted ceramic forms an adiabatic shear band after cooling.