Eutectic-reaction brazing of Al0.3CoCrFeNi high-entropy alloys using Ni/Nb/Ni interlayers

Abstract

• A lamellar C14 Laves/γ phase eutectic structure formed in the brazing seam. • The distribution and morphology of Laves/γ phase eutectic in the brazing seam were changed by tailoring the brazing temperature. • The maximum shear strength of brazed joints was up to 592 MPa, reaching 95 % of Al 0.3 CoCrFeNi base metal. In this study, a novel eutectic-reaction brazing of Al 0.3 CoCrFeNi high-entropy alloys (HEAs) 1 1 high-entropy alloys (HEAs); 2 base metal (BM); 3 Proeutectic Zone (PEZ); 4 Eutectic Zone (EZ) was investigated with a design of laminated Ni/Nb/Ni interlayers. The typical Al 0.3 CoCrFeNi brazing seam consisted of proeutectic γ, the lamellar eutectic structure composed of face-centered cubic (FCC) phase (eutectic γ) and C14 Laves, as well as a few amounts of Nb based solid solution. A high density of nanoscale ordered L1 2 (γ′) phase was precipitated within γ phase matrix. With the brazing temperature raised from 1200 to 1320 °C, the dissolution volume of Al 0.3 CoCrFeNi alloy into Ni-Nb liquid was increased. The microstructure of the brazing seam changed from hypereutectic (blocky Laves + γ phase) to eutectic (Laves + eutectic γ) to hypoeutectic structures (proeutectic γ + Laves/γ eutectic structure). The shear strength of joints was increased gradually due to the formation of eutectic lamellae and the cellular growth of proeutectic γ phase. The maximum shear strength of the joint brazed at 1320 °C for 10 min was up to 592 MPa, reaching 95% of the base metal. The joint mainly ruptured in the soft proeutectic γ phase in a ductile fracture mode.