Higher entropy-induced strengthening in mechanical property of Cantor alloys/Zr-3 joints by laser in-situ eutectic high-entropy transformation

Abstract

To effectively regulate the grain boundary infiltration in CoCrFeMnNi high-entropy alloy (Cantor alloys, HEA) caused by the violent atomic interdiffusion, the higher configuration entropy on Cantor alloys surface was designed and realized via eutectic high-entropy (EHEA) transformation. Meanwhile, to effectively alleviate the residual stress caused by the notable difference in the thermal expansion coefficient (CTE) between Cantor alloys and Zr-3 alloys, a cladding layer was applied to the HEA surface using laser cladding technology of Nb, followed by brazing to Zr-3 alloys with Zr63.2Cu filler. The cladding layer's microstructure comprised Nbss and FCC+(Co,Ni)2Nb eutectic structure, resulting from an in-situ reaction between Cantor alloys and Nb. The Nbss and FCC demonstrated good plasticity, and the (Co,Ni)2Nb Laves phase provided increased strength, endowing both good plastic deformation ability and strength of the cladding layer. Notably, the existence of EHEA in the laser cladding layer made the Cantor alloy entropy from 1.61 R to 1.77 R, greatly enhancing its thermal stability and suppressing the grave grain boundary infiltration. Joints produced via laser cladding with Nb-assisted brazing exhibited a complex microstructure (HEA/Nbss + FCC + (Co,Ni)2Nb/(Zr,Nb)(Cr,Mn)2 + (Zr,Nb)ss/(Zr,Nb)2(Cu,Ni,Co,Fe) + (Zr,Nb)(Cr,Mn)2 + (Zr,Nb)ss/Zr-3 and a significantly improved shear strength of 242.8 MPa at 1010 °C for 10 min, 42.4 % higher than that of directly brazed joints. This improvement was attributed to reduced grain boundary infiltration, alleviated residual stress due to CTE disparity, and eliminated micro-cracks in the brazing seam. This study presents an effective solution for reducing residual stresses and achieving reliable bonding between Cantor alloys and Zr-3 alloys, with potential applications in brazing CoCrFeNi-based HEA and Zr-3 due to the beneficial eutectic reaction between CoCrFeNi and Nb.