Technical And Mechanism Study On Vacuum Brazing Of ZrB₂-SiC Ceramic Composites

ZrB₂-SiC ceramic composites has been considered to be an ideal high temperaturematerial wich can be applied to high-temperature structural in aerospace field because ofits low density, excellent oxidation/ablation resistance, and high mechanical properties athigh temperature. For the poor processing performance, the directly fabrication ofZrB₂-SiC ceramic composites with large dimensions and complex shapes is diffcult,which prevents it from being used in wide application. Therefore, the development ofrobust joining techniques with itself or other high temperature material should be quitenecessary. In this paper, high quality joining of ZrB₂-SiC ceramic composites wassuccessfully realized by using TiZrNiCu and BNi₂active brazes. The influence ofbrazing parameters on microstructure and mechanical properties of joints was studied.The optimal brazing parameters were identified. The interface reaction mechanism wasalso analyzed.The typical interface structure was ZS/-Ni₂Si+β1-Ni₃Si+ZrB₂+C/Ni（s,s）+Cr_xB_yCz/-Ni₂Si+β₁-Ni₃Si+ZrB₂+C/ZS with BNi₂active brazes. When the brazing temperaturewas1160℃and the holding time was20min, the joints achieved the maximum shearstrength about121.3Mpa and the fracture position was at the diffusion layer of elenmentNi that was also the reaction layer of A. The brazing temperature and the holding timehave the same affection on the fracture position; when the holding time was short, thefracture position was at Ni（s,s） solid solution layer n the brazing seam and then extendedto the the reaction layer of A; when the holding time was long, the fracture position wasat Ni（s,s） solid solution with some β1-Ni3S phase in the brazing seam and then extendedto the the reaction layer of A.The typical interface structure was ZS/Zr（s,s）/（Ti,Zr）_xSi_yCz/TiBw+（Ti,Zr）₂（Ni,Cu）/（Ti,Zr）_xSi_yCz/Zr（s,s）/ZSwith TiZrNiCu active brazes when the brazing temperature waslow and the holding was short. With the increase of brazing temperature and the holdingtime, the thickness of the Zr（s,s） solid solution layer was growing gradually; the volumeand quantity of （Ti,Zr）xSiyCzwere also growing gradually and it might grow into thecenter of the joint; the volume and quantity of TiBwwere obviously growing and itmostly grew through the joint. the interface structure was ZS/Zr（s,s）/（Ti,Zr）_xSi_yCz+TiBw+（Ti,Zr）₂（Ni,Cu）/Zr（s,s）/ZS. When the brazing temperature was920℃and the holdingtime was10min, the joints achieved the maximum shear strength about143.5Mpa andthe fracture position was at ZrB₂-SiC ceramic composites. With the change of the brazingtemperature and the holding time, the main fracture position didn’t change and was atbase material beside to the reaction layer. All the fracture were brittle. Combined with the brazing process in each stage, the interface reaction mechanismwas analyzed. Based on diffusion theory and the diffusion of Ti atom in the solid solutionlayer, the pattern of growth for the Zr（s,s） solid solution layer was analyzed, the growthkinetics parameters was obtained, then got the dynamic equations for growth behavior ofthe Zr（s,s） solid solution layer.