Brazing Process Test And Residual Stress Analysis Of TiB₂/BN Ceramics And Copper

With the continuous progress of modern science and technology,the properties of materials in industry and life are more and more demanding,and often hope to have a good comprehensive performance.The bonding of TiB2/BN ceramics and metals can make up for some of their own performance defects while giving full play to the excellent properties of ceramics and metals.However,due to the difference of elastic modulus,line expansion coefficient,chemical bond and other factors,it will bring some difficulty to its bonding.Based on this phenomenon,this paper uses wire cutting for ceramics,and optimizes the processing of ceramics according to the two optimization goals of ceramic processing speed and surface roughness.Then the brazing connection of ceramics and copper is carried out by Cu-Ti-Sn solder,and the wetting area and wetting angle of the solder on the ceramic surface are studied by adjusting the mass fraction of Sn powder to 10wt%,15wt%,20wt%,welding temperature and heat preservation time,and the wetting of the ceramic surface is analyzed.The effect of multiple factors on wetting effect was studied.Finally,ANSYS software is used to simulate the variation of brazing residual stress between TiB2/BN ceramics and copper.The following conclusions were reached:(1)In the wire cutting process of ceramic materials,the influence of the number of effect tubes on the processing speed is very obvious,and the effect of pulse width ratio on surface roughness is very obvious.After collecting the test data and orthogonal optimization,the problems in the actual test are avoided because the processing current is too large,resulting in broken wire.After considering the machining speed and surface roughness of the specimen,the optimum process parameters are pulse width 24μs,pulse width ratio 4,5 root of the effect tube and 110 V of voltage.(2)In the active solder,the increase of Sn element will reduce the liquid phase line of the solder and promote the wetting of the solder on the ceramic surface,but the change is little after the content exceeds a certain amount,and too much Sn will cause the joint to become brittle and reduce the joint quality.The brazing temperature has a great influence on the area of solder spreading,and the high brazing temperature can speed up the diffusion of active elements in the solder,promote the interfacial reaction between the solder and ceramics,and generate the interfacial reaction layer.Welding temperature and heat preservation time have a great influence on the wetting angle,the higher the welding temperature,the longer the insulation time,the smaller the wetting angle of the solder,but the longer heat preservation time will also cause the transition flow of the solder.When the Sn content is 15wt%,the welding temperature is 920℃,the heat preservation time is 15 min,ceramics and copper can form a strong connection.(3)The results of ANSYS finite element simulation show that the change of cooling speed has a greater effect on residual stress than changing the cooling temperature when other conditions remain unchanged,so changing the cooling speed can obviously relieve the residual stress.At the four temperatures of 820℃,870℃,920℃ and 970℃,with the increase of temperature,the residual should change little.According to the simulation analysis results and the actual test situation,the selection temperature of 920℃ is guaranteed under the condition of welding success rate.The faster the cooling speed,the increase of the residual stress,the increase of shear stress is greater than the axial stress.At different cooling speeds,the increase of residual stress is not the same,the temperature from 10℃/min to 15℃/min,the increase of residual stress rate is greater than the other two intervals.The cooling speed of 10℃/min can not only achieve the goal of reducing residual stress,but also improve work efficiency and save a lot of time.The residual stress distribution of Cu-based solder and Ag solder on the solder layer and the ceramic side is similar,compared with the Ag base solder,the axial stress and shear stress of Cu-based solder are smaller.The shear stress and axial stress of the joint will change with the thickness of the solder layer,and when the thickness of the solder layer is 0.1mm,there are large shear stresses on the joint.When the thickness of the solder layer is 0.3mm,there is a large axial stress on the joint.After the combined residual stress,the filling of the solder and the three factors of the solder layer belonging to the weak area of the brazing material,the shear stress and axial stress of the joint are small when the 0.2mm is selected as the thickness of the solder layer.(4)In the X direction,there will be a large residual stress in the ceramic side distance ceramic and the solder layer combined with the surface 0.5mm.The lateral axial stress of ceramics affects the expansion ability of cracks in ceramics,and the maximum shear stress will appear at the junction of ceramics and brazing layers at the left and right ends of the joint.Ceramic lateral axial stress is roughly "W" type distribution,the residual stress at both ends is higher,the residual stress at the center line is the highest,there is a large shear stress on the left and right side of the joint,its value is equal,the direction is opposite.Through the research and analysis of this chapter,the selection of Cu-based solder,solder layer thickness of 0.2mm,welding temperature of 920 ℃,cooling speed of 10℃/min,in the case of meeting welding requirements,reduce cooling time to improve efficiency.