Healing internal cracks of C/C-SiC composite with AgCu alloy for improving C/C-SiC/Ti60 joint performance: Cu-assisted Ag transport in polycrystalline SiC

Abstract

In this work, a strategy for rapidly healing internal cracks of C/C-SiC composite was developed. Long cracks were effectively healed following treating the composite with AgCu alloy for only 20 min. The healing mechanism was investigated, and the integrity of these healed cracks after reheating was assessed. Additionally, the impacts of crack healing on the C/C-SiC/Ti60 joints were explored. Introducing Cu into Ag dramatically increased the diffusion rate of Ag in SiC by several orders of magnitude, thereby facilitating rapid mass transfer into SiC. Based on this, internal cracks of C/C-SiC composite were healed with AgCu alloy above 1500 °C. The healing agent rapidly migrating within the composite preferentially filled the cracks and generated shrinkage stress upon cooling, collectively contributing to crack closure. The migration of SiC induced by the dissolution-precipitation reaction enhanced the effect of Rayleigh instability and further healed these cracks. The healed cracks remained intact after reheating below 1300 °C and subsequent cooling, ensuring their integrity following brazing. The crack healing resulted in a 108 % improvement in the performance of C/C-SiC/Ti60 joints, attributed to the increased fracture resistance of the joints' weak region. This work was of great significance in repairing ceramic-matrix composite.