Research On Microstructure And Residual Stress Regulation Mechanism Of Al₂O₃/stainless Steel Brazed Joints

Al₂O₃ ceramics are widely used in aerospace,electronic power,chemical energy and many other fields due to their high strength,low thermal conductivity,excellent insulation and high temperature resistance,wear resistance and corrosion resistance.However,ceramics do not have good workability due to their own brittleness limitation,and it is difficult to manufacture members having a large size and a complicated shape.In industrial applications,it is often required to realize the connection between Al₂O₃ and metal to obtain a composite member having both excellent properties.However,the thermal expansion mismatch problem of the two materials seriously affects the joint quality of the ceramic-metal joint.In this paper,the hydrogenated titanium alloy is used as the intermediate layer,and the residual stress of the joint of the dissimilar materials is regulated by its thermal expansion adjustment and plastic deformation behavior.The effects of different process parameters on the microstructure and formation mechanism of the interface,the microstructure and deformation behavior of the intermediate layer,and the mechanical properties of the joint were studied.The mechanism of joint stress relieving was explained.The influence of different process parameters on the microstructure of joints was studied,and the corresponding formation mechanism was discussed.The typical joint morphology is alumina/Ti_x?Cu,Al?_yO/Ag?s,s?+Cu₂Ti/Cu-Ti diffusion layer/?-Ti+CuTi₂/hydrogen titanium alloy/?-Ti+CuTi₂/Cu-Ti diffusion layer/Ag?s,s?+Cu₄Ti/Fe-Cr phase/stainless steel.And as the temperature increases,the thickness of the diffusion layer increases,Ag element is discharged,Cu-Ti is converted into dendritic form,and a ternary phase of Cu-Ti-Fe is formed on the stainless-steel side.The thermodynamic calculations show that Ti has a more obvious diffusion tendency to Al in Ti-Al-Cu system,and the diffusion tendency of Cu to Al and Ti is similar.In the Ti-Cu-Fe system,Ti has a more obvious diffusion tendency to Fe,and the diffusion and diffusion tendency of Cu to Ti is more obvious.The microstructure and phase composition of the opposed hydrogen-titanium alloy before and after welding were studied.The content of?phase increased significantly with the increase of hydrogen,accompanied by the formation of?hydride and?''martensite.During the welding process,the hydrogenated structure is decomposed,and after the decomposition is completed,a small amount of?phase is distributed in the structure of the equiaxed?grain boundary.A large amount of dislocations and slips are generated in the titanium alloy intermediate layer during the brazing process.The mechanical properties of the joints under different process parameters were analyzed.It was found that the controlled cooling process can promote the stress relieving effect of the intermediate layer.The joint fracture path mainly includes the following three types:fracture in the ceramic matrix,fracture at the ceramic side interface reaction layer,and fracture from the brazing material to the ceramic.It was finally determined that the hydrogenated titanium alloy intermediate layer achieved the stress relief of the joint through the combination of two mechanisms of thermal expansion regulation and plastic deformation.