Study On Process Of Si₃N₄ And 316L Stainless Steel

As a structural material with high temperature resistance,corrosion resistance,high strength and other good properties,Si₃N₄ is widely used in aerospace,metal cutting,electronics and other fields.However,it is often required to produce composite assembly with metal connection in industrial applications due to its low toughness and difficult processing.Therefore,it is of great practical significance to realize the reliable connection between Si₃N₄ and metal.In this thesis,vacuum brazing of Si₃N₄ and 316 L stainless steel was carried out using conventional?Ag Cu28?Ti3.6 filler.The typical microstructure of the joint was as follows: Si₃N₄/Ti N/Ti5Si3+Ag?s,s?+Cu?s,s?+Fe2Ti/316 L.Research showed that different brazing temperature and holding time had a great influence on the microstructure and mechanical properties of joint: with the extension of the rise of temperature or holding time,the reaction layer between the parent metal and brazing seam gradually thickened.In addition,cracks gradually appeared near the ceramic joints after brazing due to the difference of thermal expansion coefficient on the ceramic side.The shear strength of joints increased first and then decreased.When the brazing temperature was 890 ?,holding for 10 min,the maximal joint shear strength was 84 MPa.In addition,the content of Ti had a great impact on the interface layer on both sides of the brazing joint.So?Ag Cu28?Tix filler with Ti content of 1.5,3.6,5.5 and 7.5 wt% was prepared for brazing Si₃N₄ and 316 L stainless steel to study the influence of different Ti content on the joint microstructure and performance.The analysis showed that with the increase of Ti content,the thickness of the ceramic side reaction layer in the joint increased gradually with the increase of Ti content and Ti-Cu compound will be generated gradually when the Ti content reaches a certain value.The joint strength first increased and then decrease.When Ti was 5.5 wt%,the strength reached the highest value 89 MPa.In order to further improve the performance,because BN can react with Ti for forming Ti N and Ti B two kinds of reinforced phase in the brazing temperature.?Ag Cu28?Ti10BN1.5,?Ag Cu28?Ti15BN2.5 and?Ag Cu28?Ti18BN3.5 were used to braze Si₃N₄ and 316 L stainless steel to study the change on joint organization and performance,and There were many holes on the surface of fracture.As divided into?Ag Cu28?Ti10BN1.5,the maximal strength was up to 69 MPa.After the optimization of Ti content,when the component was changed to?Ag Cu28?Ti10BN1.5,and the strength reached 145 MPa,which was about 70% higher than the maximum shear strength of Si₃N₄ and 316 L stainless steel joint with Ag Cu Ti,and the fracture surface became smooth.According to the mechanism of solid solution interaction between Nb and Ti,three kinds of thin films?Ti/Nb,Ti/Mo and Ti-Nb/Mo?were sputtered on the surface of Si₃N₄ by magnetron sputtering method,and conventional?Ag Cu28?Ti3.6 brazing filler metal was used to braze 316 L stainless steel.The results showed that Ti/Nb film has the highest strength of 82 MPa.The addition of Nb can dissolve in the filler and interact with Ti,Mo element failed to restrain the diffusion of Nb element to the center of brazed joint,and the fracture position was fractured on the ceramic side,and the joint still had a lot of residual stress.