Microstructure evolution and mechanical properties of diffusion bonding CoCrCuFeNi high entropy alloy to Inconel 600 alloy

In this study, the CoCrCuFeNi high entropy alloy was diffusion bonded with the Inconel 600 superalloy at bonding temperatures ranging from 950 to 1100 degrees C for a bonding time of 2 h under a pressure of 20 MPa in a vacuum. The microstructure and mechanical properties of the diffusion bonded joints were investigated. The diffusion zone of the welded joint contains of two distinct zones: a coarse grain zone (on the Inconel 600 superalloy side) and the diffusion interface layer. The blocks Cr23C6 phase and Cu-rich phase were formed in the diffusion interface layer at 950 degrees C. As the bonding temperature increased, the Cr23C6 gradually disappeared and the blocks Cu-rich phase transformed into nano Cu-rich precipitate in the diffusion interlayer at 1100 degrees C. The hardness of the interface layer was significantly higher than that of the base metal at all temperature. When the bonding temperature increased from 950 degrees C to 1100 degrees C, the ultimate tensile strength of the welded joints increased from 521 MPa to 558 MPa, and the elongation increased from 10.3 % to 31.2%, respectively. The ultimate tensile strength reached 96 % and 82 % than that of the CoCrCuFeNi HEA and Inconel 600 base metal, and the elongation is comparable to that of the base metals. All the welded joint fracture near the diffusion interface layer. As the bonding temperature increased, the fracture mode of the joint transformed brittle to ductile. At an elevated temperature of 300 degrees C, the ultimate tensile strength and elongation of the welded joint are 325 MPa and 9.8 %, respectively. The welded joint exhibits a mixed fracture mode of ductile and cleavage fractures.