Effect of Mo addition on interfacial microstructure and mechanical property of SiC joint brazed by an Ni-Si filler

Ni-based alloys provide good brazing filler characteristics for the many applications of SiC ceramics. Nevertheless, the presence of graphite is unavoidable in the reaction between Ni and SiC, leading to a significant degradation of the mechanical properties of the joint. This study investigates the effect of Mo in Ni-30Si alloy on the brazing of SiC at 1300 degrees C, to regulate interfacial reactions and reduce residual stresses by decreasing overall coefficient of thermal expansion (CTE) values throughout the brazing process. The addition of Mo up to 8 at.% efficiently suppresses graphite accumulation by converting it into Mo2C + Ni3Mo3C phases and lowering the CTE to 5.4 x 10-6/degrees C. When the Mo loading exceeds 12 at.%, the interactions between the filler and SiC are reduced as a result of the non-homogeneous dispersion of Mo. The experimental findings indicate that the joint without graphite has a lap shear strength of 107 MPa, which is nearly three times greater than the joint with graphite. Thermodynamic analyses are performed to provide a comprehensive understanding of the underlying mechanisms responsible for the formation of distinct phases in brazed joints.