Microstructure And Mechanical Properties Of Silicon Carbide Joints Brazed With High-silicon Aluminum Alloys

Due to the properties of excellent high temperature performance,low expansion coefficient,the chemical stability and good irradiation resistance,SiC/SiC composites are the promising materials for high-temperature components in advanced fusion reactors.In order to obtain large size composite parts,development of joining technology is necessary for SiC.In this work,the vacuum brazing of SiC is studied using high-silicon aluminum brazing alloys.The effect of Si content in brazing alloy on the microstructure,mechanical properties and its wettability to SiC ceramic will be discussed,then obtained the best content of Si.Adding different content of Ti and Cr elements to brazing alloy and studying the change of microstructure and mechanical properties of the brazing alloys and joints.The results showed that:（1）The microstructure of those three kinds of high Si alloys are organized by primary Si and Al+Si eutectic phase.With the Si content increases,size and quantity of the primary Si increases,and micro-hardness of alloy also increases.What`s more,AlSi alloy compressive strength,with the Si content increases,showing a gradual decrease trend,this suggests that the more eutectic organization,the stronger the compressive strength of brazing alloy.In the wettability test of SiC ceramic,Al-50 Si brazing alloy presents the best spreadability on SiC surface,indicating that 50 wt.% is the optimum Si component for the Si C ceramic connection.Therefore,use Al-50 Si brazing alloy could obtain a well-connected SiC joint,and shear strength of this joint is 73.76 MPa.（2）Adding the different content of Ti（2,6,10,14 wt.%）to Al-50 Si alloy,we could observed primary Si,Al+Si eutectic phase and new phase TiSi2,the formation of new phase reduce the volume of primary Si and make the microstructure of alloy more even.With the Si content increases,micro-hardness and compressive strength of alloys incresaes.The shear strength of SiC/Al_（50-x）-50Si-Ti_x（x=2,6,10,14）/SiC joints are greater than SiC/Al-50Si/SiC joint.When the Ti content is 6 wt.%,the shear strength is maximum at 138.98 MPa.The shear fracture of the joints are mainly composed of brittle fracture and ductile fracture.（3）Adding the different content of Cr（2,6,10,14 wt.%）to Al-50 Si alloy,we could observed primary Si,Al+Si eutectic phase and new phase CrSi2.With the Cr content increases,the primary Si decreases,and the board structure gradually thinning,microhardness of alloys increases and compressive strength of alloys incresaes.The shear strength of SiC/Al_（50-x）-50Si-C_rx（x=2,6,10,14）/SiC joints are greater than SiC/Al-50Si/SiC joint.When the Cr content is 10 wt.%,the shear strength is maximum at 186.52 MPa.The shear fracture of the joints are mainly composed of brittle fracture and ductile fracture.