A novel high-entropy filler (Ni₃₀Co₂₀Cr₂₀Mo₁₀Al₁₀Ti₁₀) for SiC_f/SiC and DD3 brazing: Enhanced joint strength via plastic phase

This study introduces a novel high-entropy filler, Ni₃₀Co₂₀Cr₂₀Mo₁₀Al₁₀Ti₁₀, and compares it with the well-known high-entropy filler (CoFeNiCrMn)₈₈Nb₁₂, which is highly compatible with SiC_f/SiC for brazing SiC_f/SiC and DD3 alloys. The results show that when (CoFeNiCrMn)₈₈Nb₁₂ is used as the filler, the FCC1/Ni(s, s) interface at the brazing center and the Ni₂Si/(Ti, Nb)C interface near the composite side exhibit non-coherent interfaces, characterized by significant lattice mismatch and poor bonding. Additionally, IFFT analysis of high-resolution TEM images, combined with nanoindentation test results, reveals that the Ni₂Si phase has limited plastic deformation ability, along with high modulus and hardness, which negatively impacts joint performance. In contrast, when Ni₃₀Co₂₀Cr₂₀Mo₁₀Al₁₀Ti₁₀ is used as the filler, although the FCC2/Ni(s, s) and FCC2/Cr(s, s) interfaces at the center of the brazing seam also exhibit non-coherent interfaces, the lattice mismatch is reduced. Additionally, the Cr₃Ni₂SiC/TiC and Cr₃Ni₂SiC/CrC interfaces near the composite material side exhibit semi-coherent interfaces with a smaller lattice mismatch, which enhances interface bonding in the brazed joint. Moreover, IFFT analysis and nanoindentation tests show that Cr₃Ni₂SiC has good plastic deformation ability, as well as low modulus and hardness, which benefit joint performance. When brazed with Ni₃₀Co₂₀Cr₂₀Mo₁₀Al₁₀Ti₁₀ filler under the same process conditions, the SiC_f/SiC/DD3 joint exhibits a clear yield stage, significant fluctuations on the fracture surface, and a shear strength of 117.1 MPa, approximately 21 % higher than that of the joint brazed with (CoFeNiCrMn)₈₈Nb₁₂ filler. This study offers insights into the development of new filler systems for brazing SiC_f/SiC composites and DD3.