Abstract:A practical process method for precise integration of SiC_f/SiC composite (CMC) and a Ni-based superalloy (K403) was proposed in this study. It involves Nb coating pretreatment of the CMC via the chemical vapor deposition (CVD) at 1000 °C and subsequent integral precision casting between the pretreated CMC and the K403 superalloy melt. The method solves the difficulty for the dissimilar material to be cast together, forming a robust bonding interface with an average shear strength of 94.8 MPa at room temperature. During the pretreatment process, the Nb reacted with the CMC, forming a reactive coating with the microstructure composed of NbC, Nb₂C and Nb₅Si₃ phases. In the following integral casting, the Nb reactive coating effectively blocked detrimental graphitization reaction between the Ni element in the superalloy melt and the CMC, and mitigated the interface thermal stress generated by both the mismatch of thermal expansion coefficients and temperature difference, resulting in the increase of interfacial strength. The typical interfacial microstructure consists of the CMC, NbC, NbSi₂/NbC, SiC, NbSi₂, Nb₂C, Nb₅Si₃, Al₄C₃, Nb₂Al/γ/γ'''' and MC (M=W, Mo, Ti). A formula for estimating the interfacial thermal stress of an integrated cast was derived.

Key words: SiC_f/SiC composite; microstructure; Ni-based superalloy; integral casting; Nb reactive coating; bonding strength