Interfacial strengthening mechanism of C/C/Nb0.74CoCrFeNi2/Nb brazed joints: Stress-relieving effects of the FCC phase

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2022-09, Vol.854, p.143895, Article 143895
• Main Authors: Hu, Jixu, Lin, Danyang, Li, Xingyi, Li, Haolong, Li, Jianguo, Tang, Zhengxin, Xi, Xin, Song, Xiaoguo, Fu, Wei
• Format: Article
• Language: English
• Subjects: Brazed joints; Brazing; Deformation effects; Dissimilar material joining; Dissimilar materials; Eutectic alloys; Eutectic high-entropy alloy; Face centered cubic lattice; Formability; High entropy alloys; High temperature; Lattice mismatch; Laves phase; Mechanical properties; Shear strength; Thermal expansion; Thickness
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2022.143895

Joining ceramics and metals has long been a key issue for manufacturing structures that are resistant to high temperature. This study joined a carbon-fiber-reinforced carbon-matrix (C/C) composite and Nb using a Nb0.74CoCrFeNi2 eutectic high-entropy alloy filler, and the evolution mechanism of the microstructure and mechanical properties of the joints were systematically studied. The eutectic structure composed of face-centered cubic (FCC) and Laves phases gradually disappeared with the increasing temperature, while the Nb(s,s) layer thickness increased gradually. The lattice mismatch was ∼97% and ∼2.8% at the Cr23C6/C/C and FCC/C/C interfaces, respectively. Considering differences in the coefficient of thermal expansion and lattice mismatch, an increase in FCC phase content at the C/C interface is conducive to reinforcing the joint strength. At 1260 °C, the combined effects of the highly deformable FCC phase and high-strength Cr23C6 increased the strength of the mixing zone, causing fracture to occur in the Nb(s,s) layer. These results are expected to contribute to further improving the joining of dissimilar materials. •The eutectic high-entropy Nb0.74CoCrFeNi2 alloy was used to join a C/C composite and Nb.•FCC exhibits superior stress relief in joints than Cr23C6.•Brazing at 1260 °C produced the most FCC phase in the brazing seam.•Joints with less FCC content exhibited weakness in the mixing area of Cr23C6 and FCC.