Effect of holding time on microstructure and mechanical properties of SiC/SiC joints brazed by Ag-Cu-Ti + B4C composite filler

The composite fillers have a number of advantages comparing with the traditional filler metals, and have been widely used for brazing ceramics. However, previous researches mainly focus on the strengthening mechanism of either whiskers or particles. It is still of great interest to investigate the reinforcement effect with the presence of both whiskers and particles. In this study, Ag-Cu-Ti + B4C composite filler was developed to braze SiC ceramics, and effects of holding time on the microstructure evolution and mechanical properties of the joints were investigated in detail. With the prolongation of holding time, the overall thickness of Ti3SiC2 + Ti5Si3 layers adjacent to SiC ceramic was increased correspondingly and the reaction between active Ti and B4C particles was promoted more extensively. The bending strength of the joints increased with holding time until the maximum bending strength of 140 MPa was reached and then decreased dramatically. The hardness and Young's modulus of the joints were characterized by nano-indentation to reveal the strengthening of the brazing seam. In addition, the strengthening mechanism of the joints brazed by the Ag-Cu-Ti + B4C composite filler was proposed on the basis of experimental observation and theoretical analysis