Improving mechanical strength of Ti-Ni-Si joints for joining carbon/carbon composites by thermal cycling treatment

Ti-Ni-Si compound was used to join carbon/carbon (C/C) composites by hot-pressing sintering. Effects of high temperature treatment and thermal shock on the bonding strength of Ti-Ni-Si joints were investigated. After the joints were treated for 10 h at 1000 °C, the average shear strength was increased to 30.89±0.75 MPa, which was 30.01% higher than the original ones, accompanied by homogeneous Ti-Ni-Si interlayer with few defects. Fracture toughness of the joints after thermal treated for 5 h possessed significant improvement from 1.44±0.32 to 4.10±0.56 MPa m^1/2 attributing to the decrease of free Si and the increase of ternary compound Ti₄Si₇Ni₄ in the interlayer. After heat treatment at 1000 °C for 5 h and thermal shock between 1000 °C and room temperature for 30 times, the average shear strength of those joints increased from 23.76±0.50 to more than 30 MPa. The improvement of the mechanical strength of Ti-Ni-Si joints was attributed to the multi-component diffusion reactions to seal the defects in the Ti-Ni-Si joints during heat treatment and thermal cycling tests. This work could provide new insight to understand strengthening of the bonding between C/C composites instead of weakening after the joints experiencing thermal shock.