Laser dissimilar welding of CoCrFeMnNi-high entropy alloy and duplex stainless steel

Abstract

High entropy alloys (HEAs) have superior mechanical properties that have enabled them to be used as structural materials in nuclear and aerospace applications. As a dissimilar joint design is required for these applications, we created a dissimilar joint between CoCrFeMnNi-HEA and duplex stainless steel (DSS) through laser beam welding; a technique capable of producing a sound joint between the two materials. Microstructure examination using SEM/EBSD/XRD analysis revealed that the weld metal (WM) exhibits an FCC phase regardless of the postweld heat treatment (PWHT) temperature (800 and 1000 °C) without forming detrimental intermetallic compounds or microsegregation. The heat-affected zone of the CoCrFeMnNi-HEA showed CrMn oxide inclusions while that of the DSS showed no inclusions. Moreover, a lower hardness was recorded by the WM compared to the base metal after welding. After PWHT, the hardness of the WM, CoCrFeMnNi-HEA, and DSS decreased with an increase in the PWHT temperature. However, the decrease in the hardness of the HEA was more significant than in the WM and DSS. The cause for this reduction in hardness was attributed to recrystallization and grain growth. In addition, a strength of 584 MPa with low ductility was recorded after welding. The obtained strength was lower than that of the BMs, but comparable to that of the welded CoCrFeMnNi-HEA. The application of PWHT resulted in over a 20% increment in ductility, with only a marginal reduction in strength. The deformation mechanism in the as-weld joint was mainly dominated by dislocation while that for the PWHT joint was twinning. We propose laser beam offset welding as a technique to improve the mechanical properties of the dissimilar joint, which will be the subject of future studies.