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

Abstract

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°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 × 10−6/°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. © 2024 The American Ceramic Society.