Joining of SiC based ceramics and composites with Si-16Ti and Si-18Cr eutectic alloys

Silicon carbide and SiCf/SiC ceramic matrix composites are attractive materials for energy application because of their chemical stability and mechanical properties at high temperature. For these materials advanced joining techniques are under development and, among them, brazing is one of the most promising. In this paper a brazing technique based on the use of the Si-16Ti (at.%) and the Si-18Cr (at.%) eutectic alloys (with 1330°C and 1305°C melting points, respectively) is presented and discussed. The eutectic alloys were prepared by several melting operations, reduced in powders and finally used for the joining experiments. The brazing trials led to joints without discontinuities and defects at the interface and with fine eutectic structures exhibiting a morphology comparable with that of the starting alloys. Microstructure and nanochemistry investigations showed neither interdiffusion nor phase formation at the interface leading to the conclusion that direct chemical bonds are responsible for the adhesion. Joint specimens showed high shear strength with failure occurring mainly in the base material.