Enhancement in interfacial bonding quality of CoCrFeMnNi high-entropy alloy vacuum hot-compression bonding via surface shot peening

Vacuum hot-compression bonding (VHCB) is an advanced solid-state bonding technique. To expand its application in high-entropy alloys (HEAs), a new strategy to enhance the interfacial bonding quality of CoCrFeMnNi HEA VHCB joints by surface shot peening (SP) was proposed, and the effects of SP treatment on the interfacial bonding behavior and mechanical properties of VHCB joints were investigated. The results revealed that SP treatment introduced a nanocrystalline layer and plastic deformation layer with non-uniform strain on the specimen bonding surface, and a hierarchical grain size gradient fine microstructure was formed by a static recrystallization process under the thermal activation condition before VHCB. During the bonding process, the fine microstructure of the SP-treated layer was retained and provided a large number of grain boundaries and dislocations, which facilitated atomic diffusion and plastic flow in the interfacial region and promoted the closure of interfacial voids and the dissolution of interfacial oxide particles. Additionally, interfacial crystallographic and tensile test analyses indicated that the SP treatment induced a multiple interfacial grain boundary (IGB) migration mechanism in the VHCB joints, which dramatically improved the IGB migration level and ultimately led to a complete recovery of the mechanical properties of the CoCrFeMnNi HEA VHCB joints.