Reaction mechanisms and mechanical properties of SiCf/SiC composite and GH536 superalloy joints using CoFeNiCrMn high-entropy alloy filler

Abstract

To meet the service conditions and strength requirements of turbine stator blades and the inner and outer rings of aero engine casings, CoFeNiCrMn high-entropy alloy filler was used to braze SiC_f/SiC/GH536 joints. This study investigated the effects of holding time on the joints' microstructure and mechanical properties. Key phases identified in the welded joints include MoNiSi, FCC, and Cr₂₃C₆ near the composites, with brittle Ni₃Si and Fe₂Si intermetallic compounds forming due to filler diffusion. Optimal brazing parameters were found to be 1220 °C for 30 min with a shear strength of 64.28 MPa. The study also highlighted that increased holding time at the same temperature enhances diffusion at the joint, increasing brittle intermetallic compounds, initially improving shear strength, which then declines. Microstructural and fracture morphology analyses revealed that insufficient insulation time leads to poor welding and stress concentration at pores, causing cracks. Excessive insulation time results in joint fractures due to the brittleness of Ni₃Si and Fe₂Si intermetallic. Thus, joint shear strength correlates with welding quality and intermetallic compound distribution.