Microstructure and strength of diffusion bonding W alloy/304 stainless steel joint using a Cu interlayer

To realize the high-performance diffusion bonding of W alloy (90 W-7Ni-3Cu) with 304 stainless steel (304SS), the microstructure and mechanical properties of the solid diffusion bonding joints of W alloy and 304SS with a pure Cu interlayer were conducted at 900 degrees C, 20 MPa and 2 h. The results showed that the solid diffusion bonding with a Cu interlayer, can achieve a reliable bonding between the W alloy and 304SS. Furthermore, all the interfaces have excellent bonding through mutual diffusion of atoms at the W/Cu and Cu/304SS interfaces. No intermetallic compounds, or other brittle phases were formed in the bonding area. At the W/Cu interface, the interplanar spacing increased due to the diffusion of Cu atoms into the W lattice. Moreover, a nano-indentation test across the joint interfaces demonstrated the effect of solid-solution strengthening and strain hardening in the 304SS/Cu diffusion zone. The tensile strength of the joint was as high as 265 MPa, which was about 58% higher than for the joint without a Cu interlayer. The fracture analysis showed that the mixed fracture mode of plastic fracture and intergranular fracture occurred in the Cu interlayer and at the Cu/304SS interface. Mechanical tension tests revealed the enhanced strength of the joint with a Cu interlayer.