High-temperature joining properties of Nb_0.74CoCrFeNi₂ high-entropy filler for brazing ceramic matrix composites and metals

Nb_0.74CoCrFeNi₂ high-entropy powder filler was used to braze C/SiC composites andGH4169, and the effects of brazing temperature and holding time on the microstructure and shear strength of the joints were systematically investigated to reveal the formation mechanism of the joints. It was found that the typical structure of joint is Cr₂₃C₆+(Cr,Fe)₂₃C₆/(Cr,Fe)₃C₂+Ni₂Si+NbC/FCC+(Cr,Fe)₃C₂+Ni₂Si. With the reaction progressing on the side interface of the composite material, the Cr element was gradually consumed, forming a unique gradient interfacial structure, which is conducive to the relief of residual stresses in the joint. With the increase of brazing temperature or the prolongation of holding time, the internal defects of the joints gradually disappeared, but the thickness of the brittle interfacial reaction layer increased sharply, resulting in the joint shear strength showing a tendency of first increasing and then decreasing. When the brazing temperature is 1260 ℃ and the holding time is 25 min, the shear strength of the brazed joint is up to 188.1 MPa, and high-temperature shear strength up to 107.7 MPa at 800℃, and still 57.6 MPa at 1000℃. The high shear strength originates from the diffusion of Ni element from the brazing material into the SiC matrix of the composite material, which forms a strong interfacial bond between the fiber bundles and the matrix.