Research on the interfacial reaction behaviors and mechanical properties of W/ODS steel laser brazed dissimilar joints assisted by CoCrFeNiCu high entropy alloy interlayer

In order to improve welding efficiency and achieve flexible manufacturing of the divertor components for tokamak devices, laser welding-brazing was employed to join W and oxide dispersion strengthened (ODS) steel. Due to the significant differences in the physical properties between W and ODS steel as well as the formation of brittle intermetallic compounds (IMCs) at the interface, achieving a reliable joint presents substantial challenges. High-entropy alloys (HEAs) exhibit high-entropy and sluggish diffusion effects. To mitigate elemental reaction and diffusion at the W/ODS steel interface, a 0.8 mm thick CoCrFeNiCu HEA interlayer was introduced to assist the welding process. Then, process parameter optimization was conducted to obtain a high-performance W/CoCrFeNiCu/ODS steel joint. The final results demonstrated that, after process optimization, the reaction layer thickness at the interface was reduced from 6.9 μm to 1.4 μm with the addition of the CoCrFeNiCu HEA interlayer, and the interfacial microstructure transformed from Fe₂W-IMCs to a Fe-based solid solution. The fracture mode of the joint evolved from a single brittle fracture mechanism to the coexistence of two distinct modes: ductile–brittle mixed fracture and brittle fracture. The optimized weld joint achieved an average tensile strength of 212 MPa, representing a 41% increase compared to the direct laser welding-brazed W/ODS steel dissimilar joint without an interlayer.