Microstructure characteristics and mechanical properties of TiAl alloy joint brazed with CoCuFeNiTi1.2V0.4 high entropy alloy filler

Abstract

In this study, a high entropy alloy CoCuFeNiTi1.2V0.4 was used as a novel brazing filler metal to braze the TiAl alloy. The microstructure and formation mechanism of TiAl joints were comprehensively investigated, and the effect of brazing temperature on the interfacial microstructure and mechanical properties of the joints was analyzed. The results showed that the joint interfacial formed three different zones with symmetrical characteristics after brazing. The joints were primarily composed of an intermetallic compound phases and high entropy solid solution phases. Ti-rich BCC phase and Cu-rich FCC phase are formed in the brazing seam center zone, which not only improves the strength and plasticity of the joint but as well as releases part of the residual stress. However, the reaction and diffusion of atoms at the interface would break the high entropy effect, and the compound layers could easily form under the conditions of concentration gradient and high temperature. With the brazing temperature increased, the thickness of B2 layer and τ3 layer in the seam increased and the bulk Cu-rich phase internal the seam center basically disappears. In addition, the amount of τ2 compounds precipitated in the B2 phase significantly increased at higher brazing temperatures. The maximum shear strength of the joint was 143.4 MPa when brazed at 1120 °C for 20 min.