A designed FeCoNiCuTiV high-entropy filler metal toward achieving superior interfacial bonding Ti2AlNb alloy

Abstract

As a critical material of next-generation aircraft, joining Ti₂AlNb alloy has emerged as a key in demanding structural applications. Herein, a novel FeCoNiCuTiV high-entropy filler metal was designed for vacuum brazing of Ti₂AlNb alloy, inhibiting the formation of continuous brittle intermetallic compounds (IMCs) due to the role of high mixing entropy. Typical interfacial microstructure of the brazed joint was Ti₂AlNb/B2 + (Ti, Nb)₃Al/Ti₂AlNb phase dissolved with Fe, Co, Ni and Cu + Ti₃Al + (Ti, Nb)₃Al + Nb₂Al + Ti-rich IMC/B2 + (Ti, Nb)₃Al/Ti₂AlNb. The dissolution of the Ti₂AlNb alloy induced the formation of the Nb₂Al phase at the interface under excessive brazing temperature, leading to the destruction of the high-entropy system of the filler metal. Elevated brazing temperature promoted the uniformity of the brazing seam microstructure and eliminated the residual brazing zone. The maximum strength of 235.9 MPa was reached at 1150 °C for 10 min. Nanoindentation and fracture path revealed that the diffusion zone was the weak zone of the joint and that the formation of (Ti, Nb)₃Al phase perpendicular to the interface contributed to the strength of the joint. The fracture mode of the joint was a brittle fracture with cleavage fracture characteristics. This work shed light on opening up a wider field of high-entropy alloys as filler metals, which also provided references for accelerating the practical applications of the Ti₂AlNb alloy.