Achieving high-strength joining with superior metallurgical bonding in tungsten/steel via in-situ element-selective directional diffusion

To address the weak metallurgical bonding at interfaces in traditional tungsten (W)/steel joints with copper (Cu) interlayers, this study proposes a strategy of in-situ element-selective directional diffusion, achieving high-strength metallurgical transition bonding at both W/Cu and Cu/steel interfaces. Specifically, by introducing a Cu-Ge interlayer at the W/steel interface, multi-physics-driven forces (gravity and temperature fields) were utilized to enable the selective directional diffusion of Fe and Cr from the steel across the Cu-based interlayer. These elements migrated through the Cu interlayer, forming an Fe-rich deposition layer at the W/Cu interface, realizing a metallurgically bonded W/Fe/Cu transition. Furthermore, compared to the brittle Fe₂W phase typically formed at conventional W/Fe interfaces, this study achieved in-situ toughening of the Fe₂W phase through lattice distortion and stacking faults engineering. Simultaneously, the entire distribution of Cu along steel grain boundaries formed a discontinuous reticulate Cu/steel heterostructure, effectively addressing the low bonding strength of conventional Cu/steel interfaces. Ultimately, an unprecedented shear strength of 380 MPa was attained. This work elucidates the mechanisms of interfacial metallurgical bonding, strengthening, and in-situ modification of brittle phases in dissimilar metal joints with significant thermophysical property differences. It provides a novel pathway for high-strength metallurgical joining of dissimilar metals in harsh service environments and offers new insights into the modification and toughening of brittle phases at welded interfaces.