Microstructural evolution and mechanical properties in the self-propagating brazing joint of Al0.1CoCrFeNi HEAs and 304 SS using reactive multilayer nanofoils

In this study, an FCC + BCC dual-phase solid solution structure HEAs joint was formed during self-propagating brazing using an Al/Ni nano-multilayer. The reactive Ni/Al multilayers after ignition generates heat that is used to transform the Al/FeCo/NiCr multilayer structure into a disordered HEAs layer. The effect of external pressure on the microstructure and mechanical properties of Al0.1CoCrFeNi/HEAF-304SS joints were first studied. During brazing, the formation of a solid solution zone was ascribed to the interdiffusion of atoms at the joint. The typical interfacial microstructure of the joint mainly includes Al-Ni-rich BCC, Co-Cr-Fe-rich FCC phases, and a minor amount of Al5Fe2 IMCs. With the increment of external pressure, the shear strength presented a trend of improvement, and the fracture behavior transformed from the cleavage fracture to ductile fracture. The highest shear strength of 156.8 MPa was achieved when the joints were brazed at 1050 °C for 60 min under a pressure of 40 MPa, and the joint fracture behavior was ductile. The strengthening mechanism of the joint was ascribed to the high-entropy solution strengthening mechanism in the joint. This work provides a new method for joining 304SS and HEAs, and is breaking a new ground in fabrication of HEAs-brazed joints. It is expected to be applicable in high temperature (≤800 °C) and irradiation resistant environments.