Interfacial microstructure evolution and mechanical behavior of W/steel joints diffusion bonded with CoCrFeNi interlayer

In the nuclear industry and military field, diffusion bonding between tungsten (W) and steel has received extensive attention, in which selecting and developing new joining materials is of great significance. In this paper, a high entropy alloy CoCrFeNi with excellent ductility and high melting point, is used as interlayer material for the electric -field assisted diffusion bonding between W and steel. Effects of diffusion bonding time on interfacial microstructure and mechanical performance was investigated. Under the diffusion bonding conditions of 950 degrees C for 5, 15, 30 and 45 min, no cracks or discontinuities appeared in the joints. Element diffusion occurred at interfaces and metallurgical bonding was realized between interlayer and substrates. At W/CoCrFeNi interfaces, in addition to the solid solution phase, intermetallic compounds were detected for the joint bonded with holding time longer than 30 min. Only solid solution phase formed for all the CoCrFeNi/steel interfaces. The room temperature tensile strength of the W/CoCrFeNi/steel joint was determined to be 270 MPa, exceeding the values documented in prior studies. The elevated temperature (400 degrees C and 600 degrees C) tensile strength was found to be higher than that at room temperature. In addition, similar microhardness distribution across the joints bonded for different holding times were observed, and there was no obvious difference in the hardness of the interlayer and metal substrates in these joints.