Study On Welding Process Of Oxide Ceramics And Stainless Steel

Welding parts of metal and ceramic have the excellent properties of both,so the combination of this two materials is very important due to the widely use in the manufacture industry.For instance,the outer structure of the space station in the aerospace and related transportation,turbocharged rotors,spark plugs,and various insulating components of the vehicles and so on.The most common application cases of ceramics are oxide ceramics and nitride ceramics while metals are stainless steel and titanium alloys.Al₂O₃ ceramic has low coefficient of thermal expansion,high thermal conductivity and excellent electrical insulation properties,which led to its natural qualities of high strength,high hardness,excellent wear resistance,corrosion resistance,high temperature resistance and other mechanical properties.ZrO₂ceramic shows good chemical stability and oxidation resistance,low thermal conductivity,good impact resistance and sinter resistance,and is widely used in aerospace,biomedical and other fields.Austenitic stainless steel has good mechanical properties,excellent corrosion resistance and good heat resistance especially in oxidizing environment.Based on the excellent properties of these materials,the project about welding heterogeneous materials of Al₂O₃ ceramics,ZrO₂ ceramics,and austenitic stainless is meaningful.In the process of ceramic and metal welding,the mechanical properties of the joints are low and with high probabilities of failure due to the large difference in thermal expansion coefficients and large residual stresses of the welded joints.Reducing the residual stress and improving the mechanical properties of the welded joints have become critical issues for the welding of heterogeneous materials.This project intends to use Au₈₀Sn₂₀0 solder with low melting point and Al/Ni energetic multilayer film grown by magnetron sputtering as external heating source to weld stainless steel and Al₂O₃ ceramic,and to study the mechanical properties of Al/Ni multilayer films with different modulations on welded joints and its influence on interface structure.The preliminary step is to apply the flash-fire method to weld stainless steel-ferrite ceramics and stainless steel-ZrO₂ ceramics without using solder and metal layers.The effects of auxiliary on the performance and structure of the welded joint were studied.?1?The AuSn alloy was grown by magnetron sputtering as the solder layer and the Al/Ni energetic multilayer film was used as the heat supply layer to realize the heterogeneous soldering between stainless steel and Al₂O₃.The morphology and basic properties of the AuSn alloy and Al/Ni energetic multilayer films were investigated by field emission scanning electron microscope?SEM?,X-ray diffractometer?XRD?and differential scanning calorimeter?DSC?.The mechanical properties of the welded joints were tested by a universal testing machine.The results are as follows:the mass ratio of AuSn alloy is around 80:20,the layered structure of the multilayer film is clear and the heat of reaction reaches 1239 J/g.Studies have shown that only AuSn solder has a shear strength of 46 MPa.After increasing the Al/Ni energetic multilayer film,the shear strength can reach 90 MPa and the strength is increased by about one time.The microstructure and phase structure of the welded joints show that the increase of shear strength is mainly due to the additional energy provided by the Al/Ni multilayer film,which makes the reaction at the interface intense,and the reaction between the ceramic metallization layer and the intermediate layer is intensified,and new reaction products formed.The fracture mode of the joint changed from interface fracture to compound fracture,which including intergranular fracture and transgranular fracture.?2?The welding process of stainless steel and ferrite ceramics using flash joining method was explored.When the particle size of the powder is nanometer,it is more conducive to flash forming.Under the action of an electric field,there are a large number of holes in the micron-size ferrite ceramics.The low density causes obvious cracks at the interface of the welded joint.Due to the existence of cracks,the mechanical properties of the welded joint cause large influences.In addition,there is no reaction at the joint interface.Ceramic and stainless steel are welded only by simple atom diffusion.When nano-size powders are welded with stainless steel,not only the joints have good interface morphology without gaps and holes,but the new phase layer—Cr₂O₃ layer is also formed at the interface of the welded joint,which intensifies the interface reaction between ceramics and metals and is helpful to improve the mechanical properties of the joint.?3?Preliminary research in the flash-welding experiments of stainless steel and ZrO₂ceramics showed that when the DC power source with constantly current density is used to meld,the temperature at the flash-fire increases with the condition of the decrease of electric field,and the ablating on the interface between ceramic and metal is much weaker.During the welding process,the ZrO₂ ceramic changed from white to black due to the migration of oxygen vacancies and the generation of ZrO_2-x.