Metallurgical behavior and joining characteristics of NbSS/Nb5Si3 composite joints by newly developed Ti-Ni-Nb-Zr-Hf high-entropy filler alloy
摘要
Refractory NbSS/Nb5Si3 composite has garnered significant attention for aeronautical applications owing to the exceptional high-temperature mechanical property stability. In this study, a novel Ti-Ni-Nb-Zr-Hf high-entropy filler alloy was designed for joining of NbSS/Nb5Si3 composite. The joints brazed at 1260 °C for 10 min revealed a multi-phase interfacial microstructure comprising residual low-melting-point NiTi2 intermetallic, (Nb,Ti,Zr)SS solid solution, and Nb5Si3 intermetallic. Remarkably, extending the isothermal holding duration to 60 min facilitated complete elimination of the NiTi2 phase through interdiffusion, concurrent with a phase transformation from α-Nb5Si3 to γ-Nb5Si3 within the joint region. The orientation relationship between NbSS and γ-Nb5Si3 phase was identified as [013] NbSS//[− 1101] γ-Nb5Si3, (200) NbSS//(1–102) γ-Nb5Si3. The diffusion of Ni into the NbSS/Nb5Si3 substrate followed the Arrhenius law as D = 5.463 × 10−2 exp(− 315,994/RT). Detailed atomic scale analyses revealed that Ni, Si, Zr, and Hf were enriched in the γ-Nb5Si3 phase, while Al, Nb, and Ti were segregated into the NbSS. Combined with first-principles calculations, the increase in Zr content gradually improved the ductility. The joints brazed at 1260 °C for 60 min exhibited three-point bending strengths of 349 MPa at room temperature and 150 MPa at 1200 °C.