Interfacial microstructure evolution and bonding mechanism transformation of CoCrFeMnNi high-entropy alloy joints fabricated by vacuum hot-compression bonding

Vacuum hot-compression bonding (VHCB) is a promising solid-phase bonding technology, but its feasibility and applicability in high entropy alloy (HEA) are still unclear. Herein, the VHCB process of CoCrFeMnNi HEA was investigated, and the interfacial bonding quality was comprehensively evaluated via microstructure characterization and tensile test. Results exhibit that the VHCB enables to obtain the high-quality CoCrFeMnNi HEA joints, and the excellent bonding performance is attributed to the dissolution of interfacial oxide particles (IOPs) (MnCr2O4) and the migration of interfacial grain boundaries (IGBs). The bonding quality results suggest that the sluggish diffusion of the dissolved elements resulted in partial nanoscale IOPs remaining at the original bonding interface, and the mechanical properties of the joints were not compromised when the IOPs were smaller than 35 nm in size and less than 15/100 μm in amount. Crystallographic analysis indicates that the migration behavior of IGBs is closely associated with the evolution of recrystallized grains and twin boundaries in the interfacial region, and the migration mechanism transformed with the rising bonding temperature. Furthermore, a new interfacial bonding mechanism, i.e., twin-induced interfacial boundary migration, was revealed and its beneficial effect on interfacial bonding quality was demonstrated.