Effect of Bonding Temperature on the Interfacial Microstructure and Mechanical Properties of W/Steel Joints Diffusion-Bonded with a CoFeNi Interlayer

Realizing the reliable bonding of tungsten (W) and reduced activation ferritic/martensitic (RAFM) steel is of significance for the fabrication of plasma-facing components in fusion reactors. Considering the significant differences in physical and chemical properties between the substrates of W and RAFM steel, the development of novel joining materials has attracted much attention in recent years. In the present work, a medium entropy alloy CoFeNi interlayer was selected to diffusion bond W and RAFM steel by utilizing an electric field-assisted joining technique. The effect of bonding temperature on the interface microstructure and mechanical properties of the joint was studied at room temperature. For the joints diffusion-bonded in the temperature range between 800°C and 1100°C for 15 min under 20 MPa, good metallurgical bonding without cracks and discontinuities were achieved at both the steel/CoFeNi and CoFeNi/W interfaces. Face-centered cubic (FCC) solid solutions were formed at the steel/CoFeNi interface, while both FCC and μ phases were identified at the CoFeNi/W interface. The W/CoFeNi/steel joint diffusion bonded at 900°C has the highest tensile strength of 313 MPa. Moreover, the comparison of the joint tensile strength between this work and previous researches has been discussed.