Microstructural evolution, bonding mechanism and mechanical properties of AlCoCrFeNi2.1 eutectic high entropy alloy joint fabricated via diffusion bonding

Abstract Eutectic high entropy alloys exhibit both high strength and remarkable plasticity. To explore their potential engineering applications, AlCoCrFeNi2.1 eutectic high entropy alloy was diffusion bonded, and the element diffusion behavior, interfacial microstructure evolution and mechanical properties of the resultant joints were studied. With the increase of bonding temperature, the voids gradually decreased and the dominant mechanism of voids disappearance transformed from interfacial diffusion to viscoplastic deformation. While increasing the bonding temperature to 1050 °C, the interface disappeared and a continuous solid solution structure formed at the original interface, which was beneficial for improving the joint strength. Meanwhile, the voids still existed at the interface near the B2 phase due to the synergistic effect of low diffusion rate of elements and inferior plasticity in B2 phase. The shear strength of the joints increased and the fracture mode gradually transformed from brittle fracture to ductile fracture with increasing the temperature. The highest shear strength joint of 648 MPa could be obtained at 1050 °C, which was equal to that of base metal, and the uncoordinated deformation between FCC phase and B2 phase resulted in the appearance of cleavage planes and dimples on the fracture surface at 1000 °C.