Investigation on regulating inter-granular penetration in CoCrMnFeNi high-entropy alloy and 304 stainless steel dissimilar joints

Abstract

The inter-granular penetration inside CoCrMnFeNi high-entropy alloy (HEA) in the dissimilar brazing joint of 304 stainless steel and this HEA were regulated for the first time by using Ag72Cu as filler metal (FM) and by annealing HEA. The as-rolled HEAs were annealed at a series of temperatures for 1 h before brazing. The microstructural evolution of the dissimilar joints found that penetration was reduced with increasing annealing temperature because of the consistent decreases in grain boundary density, which reduces the channels for penetration, and the gradually stable grain boundaries in HEA, which decreases the driving force of inter-granular penetration. The direct inter-diffusion between the HEA grain and FM was limited. HEA atoms in FM originated from the dissolved HEA during brazing, manifesting the acceleration of penetration on the inter-diffusion between HEA and FM. Regulating inter-granular penetration in the dissimilar joint decreased the stress concentration at the HEA side and ensured the solution-strengthening effect of Mn in FM and the contact area between FM and HEA. The tensile strength of the dissimilar joint with regulated inter-granular penetration could reach 514.98 MPa and is considerably higher than that of the joint with few penetration, which hints that penetration does not always impair the mechanical performance of joints.