Thermal-shock-induced failure in brazed joints between SiC_f/SiC composites and GH536 superalloy: Phase transition and oxygen intrusion

The investigation evaluated the thermal shock resistance and failure mechanisms of three brazed joints when exposed to 780 °C. During exposure, oxidation of the SiC_f/SiC composite leads to the formation of SiO₂. Residual oxygen will penetrate the high-entropy alloy while retaining its Face-Centered Cubic (FCC) structure. Additionally, the FCC Cr₂₃C₆ phase adjacent to the composite reacted with SiC, producing hexagonal Cr₂C, compromising the ability of joint to withstand plastic deformation. Moreover, the presence of Nb (s, s) and significant MoNiSi phases induced a gradual alteration in the Coefficient of Thermal Expansion (CTE), facilitating the initiation of shear fractures from the composites towards the central region of the seam, significantly affecting the overall structural integrity and failure behavior of the joint under thermal shock conditions. With an increase in the number of thermal shocks, the shear strength of joint gradually decreases, reaching a maximum of 22.36 MPa after 30 thermal shocks, surpassing that of some joints using glass fillers.