Microstructure and mechanical properties of W/steel joints diffusion bonded with Nb and Nb/Ni interlayers by spark plasma sintering

Tungsten/steel joints are desired for fusion reactors and militarily applications, as it could combine the unique properties of these two dissimilar metals. In view of the large differences of physical and chemical properties between W and steel, diffusion bonding is considered to be the proper technique for joining of W to steel. In this paper, diffusion bonding of W to low activation ferritic/martensitic steel at 1050 degrees C with 50 MPa for 20 min by spark plasma sintering (SPS) were investigated. The results showed that direct diffusion bonding of W to steel was feasible. However, the formation of ferrite and carbide at the W/steel interface lowered the joint strength. Effects of the insertion of ductile interlayers (Nb, Nb/Ni) on the joining interface microstructure and mechanical properties of W/steel joints were studied. The detailed microstructural characterization revealed that Nb could prevent the formation of ferrite and carbide at the W/steel interface. The Ni promoted the interfacial diffusion between Nb and steel. The shear strength and Vickers hardness of the joints were evaluated.