Microstructural characteristics and mechanical properties of IC10 superalloy and (CoCrNi)₉₄Al₃Ti₃ MEA joint brazed using NiCrSiB filler

This study focuses on the brazing of IC10 Ni₃Al-based superalloy to (CoCrNi)₉₄Al₃Ti₃ medium-entropy alloy (MEA) using a NiCrSiB filler metal. The microstructure of the brazed joint was comprehensively investigated, and the forming mechanism of the joint was elucidated. The mechanical properties and fracture behavior of the joint were evaluated. The diffusion of boron from the filler to substrates led to the diffusion-affected zone (DAZ), and the M₃B₂- and M₅B₃-type boride were precipitated with the coherence of (3 1 0)_BCT//(2 0 0)_FCC (M₃B₂) and (0 0 2)_BCT//(2 0 0)_FCC (M₅B₃) adjacent to the IC10 and MEA substrate, namely the DAZ I and II respectively. In addition, the edge dislocation reduced the mismatch between the M₃B₂ boride and the γ matrix. The isothermal solidification zone (ISZ) was formed near the DAZ when the liquidus temperature reached the brazing temperature due to the diffusion of boron and Si and the dissolution of substrates. The formation of ISZ was effectively activated at high brazing temperatures (1090, 1120, and 1150 °C). The athermal solidification zone (ASZ) was detected in the joint brazed at adopted temperatures, which mainly dominated by eutectic reactions and driven by cooling. The ASZ decreased shear strength of the defect-free joint, and readily accelerated initiation and propagation of cracks. The maximum shear strength of 554 MPa was obtained when the joint was brazed at 1120 °C for 10 min. The fracture mainly occurred in the ASZ (semi-cleavage), and passing through the DAZ (semi-cleavage) and ISZ (dimples).