Investigation on the microstructure and mechanical properties of CoCrFeNi high-entropy alloy joint bonded with BNi2 interlayer

Abstract

• The athermal solidification zone and isothermal solidification zone of CoCrFeNi joint are determined to be γ phase and high entropy Ni-rich FCC phase, respectively. No eutectic products containing borides precipitated in the athermal solidification zone. • With increasing the bonding temperature or prolonging the holding time, the growths of ISZ and DAZ present a synchronous trend. The precipitating location of CrxBy is changed from grain interior to grain boundaries. • The maximum bonding strength of CoCrFeNi joint is ∼ 429 MPa, which is about 75 % of base metal strength. • The impact of Cr depletion on the performance of CoCrFeNi joint is less severe than that on conventional alloys joints. The strategy of bonding high-entropy alloys (HEAs) is of vital significance for producing complex engineering components available to extreme conditions. In this work, transient liquid phase (TLP) bonding was applied to join CoCrFeNi HEAs using an amorphous Ni-Cr-Si-B interlayer (BNi2). The interfacial microstructure evolution, mechanical properties and bonding mechanism of the joints were evaluated. Results indicated three reaction products in the different zones of joints, including the γ phase in the athermal solidification zone (ASZ), high-entropy Ni-rich face-centered cubic (FCC) phase in the isothermal solidification zone (ISZ) and a high density of CrxBy precipitates with different morphologies (blocky, punctate and acicular) in the diffusion affected zone (DAZ 7 ). With increasing the bonding temperature or holding time, the width of ISZ and DAZ almost presented a synchronous growing trend, and the location of CrxBy precipitates was changed from grain interior to grain boundaries. Tension shear test showed excellent bonding strength of all the bonded joints due to the formation of the ASZ free of eutectic products containing borides, and the maximum bonding strength could reach 429 MPa, which is about 75 % of the base metal (BM) strength. The joint ruptured at the CoCrFeNi BM adjacent to the lapping area in ductile fracture mode. This work is expected to facilitate the fabrication and repair of complex CoCrFeNi-related components in future.