Study On Technology And Mechanism Of Joining (C_f-SiC_f)/SiBCN Ceramic To Niobium

(C_f-SiC_f)/SiBCN is an ultra-high temperature ceramic which is modified,the performance has improved significantly.In view of its high-temperature characteristics,the ceramic has a wide range of prospects in the field of aerospace and other applications.In order to solve the limitation of its size and shape with current sintering process and expand the scope of use,this paper proposes two methods of brazing and indirect diffusion welding to realize the connection of SiBCN and Nb.The interfacial microstructure of the joints was determined,and the influence of the process parameters on the microstructure and mechanical properties of the joints was analyzed.In this paper,the connection mechanism of Ti ZrNiCu directly brazing SiBCN/Nb was studied.When the brazing filler is melted,the active elements of Ti and Zr in the brazing filler were enriched on the surface of the ceramic material and reacted with SiC and BN（C）firstly which belongs to ceramic material.The Nb metal diffused into the brazing filler layer and formed a solid solution with Ti.The interfacial microstructure of the joint is: SiBCN /TiC+ZrC/Ti₅Si₃+Zr₅Si₃/（Ti,Zr）₂（Cu,Ni）/Ti-Nb solid solution/Nb,During the brazing process,SiC is decomposed by the Cu in the brazing filler,which causing Cu infiltration to the ceramic material.Two kinds of high-temperature brazing filler were designed and prepared,including Pd-Ag and Pd-Ni.DSC differential thermal characterization of the two brazing filler were 1240°C and 1250°C.Using the two kinds of Pd-based brazing filler directly brazed SiBCN/Nb,and the joint wasn’t achieved due to the large amount of Ag in Pd-Ag brazing filler volatiling under high vacuum and high temperature.The connection mechanism of Pd-Ni directly brazing SiBCN/Nb was studied.The Ni and Pd elements in the brazing filler were enriched on the surface of the ceramic material and reacted with SiC and BN（C）.Ni elements preferentially reacted with Nb metal,and formed a two-layer reaction layer at the interface.The interfacial microstructure of the joint is: SiBCN/Ni₂Si+Pd₂Si/Pd-Ni/NbPd₃+Ni₆Nb₇/NbNi₃/Nb,but the surface of the base metal was seriously deformed due to the reaction is too severe.The method of introducing the barrier layer on the ceramic surface was proposed.The surface of the ceramic was metallized by magnetron sputtering method.In order to improve the bonding strength between the coating and the ceramic material,the orthogonal test was designed to optimize the technological parameters of the sputtering.The problem of over-reaction still existed after coating on the surface.In this paper,the indirect diffusion welding to connect SiBCN/Nb with Pd-Ag interlayer was proposed.When the welding temperature was 1000°C,the joining of the two kinds of base materials was realized.But a portion of Ag in the interlayer volatiled in the welding process.In order to reduce the welding temperature,the ceramic surface was metallized,and Ti and Cr coating were respectively introduced by magnetron sputtering method.When Ti coating is used,the two reaction layers were formed in the coating during the diffusion welding process.The fracture position of the joint occurred inside the coating.When Cr coating is used,a plurality of phases were dispersed in the coating during the diffusion process,and the fracture position of the joint occurred inside interlayer or ceramic material.The mechanical properties of the joints under the two kinds of coating conditions were co MPared,and the shear strength at the joints of the SiBCN surface which was sputtered by Cr was higher.