Microstructure and properties of the C/C-superalloy brazed joint by Ni-based filler

Abstract

Stable and reliable C/C-superalloy joints that can withstand high-temperature service will become extremely important. Ni-based filler was employed for successful brazing of C/C composites and In738LC superalloy in this study. The brazed joints contained isothermal solidification zone (ISZ), diffusion affected zone (DAZ), and penetration zone close to the C/C side. The ISZ contained lots of carbide-borides besides Ni(s,s) and Cr(s,s). The specific composition and atomic arrangement of these phases were characterized by the focused ion beam (FIB) method and transmission electron microscopy (TEM) analysis. Results showed the obvious lattice distortion of the Ti–Mo–B compound indicated the presence of the severe internal residual stress. The microhardness distribution of the brazed joint was analyzed in combination with the microstructure. Brittle Cr–Ti–Mo carbide-borides formed in the reaction layer contributed to the high microhardness, and the shape of borides influenced the DAZ microhardness significantly When the brazing temperature was 1100 °C, the highest joint shear strength was obtained due to a matched proportion of the width and the microhardness of ISZ.