Abstract: The crux of molybdenum/Fe-base alloy welded joint is embrittlement and consequently deteriorated strength. The current researches just attribute it to brittle intermetallic compound inside the weld. However, no brittle phase continuously precipitates at the fracture location of the molybdenum/Kovar alloy electron beam welded joint, meaning that the unstable phase interface is the real fundamental reason for the brittleness of joint, instead of the phases themselves. Noncoherent interfaces are formed between α-Mo and eutectoid α-Fe + μ(Fe₃Mo₂) deriving from solid-state phase transition. To optimize interfacial coherence and stabilize the interface, CoCrCuFeNi high entropy alloy is added into the weld. The new interfaces between α-Mo and eutectic face-centered cubic (fcc) + laves are transformed into coherent interfaces. σ(FeCr) nanoparticles precipitate at α-Mo/fcc interface, indicating the decreased interfacial energy and more stable interface. The tensile strength of the joint is increased from 262 to 366 MPa. The present work provides guidance for optimizing welding quality between molybdenum and Fe-base alloy.

Key words: Electron beam welding, Molybdenum, High entropy alloy, Interfacial stabilization, Nano-scale particle