Enhancement of Hardness and Yield Strength Induced by Cu-Rich Phase and Its Effect at Cryogenic Temperature on Gas Tungsten Arc Welds of Ferrous Medium-Entropy Alloy

This study investigated the gas tungsten arc (GTA) weldability of a base metal (BM) Fe 60 Co 15 Ni 15 Cr 10 medium-entropy alloy (MEA) by applying CoCrFeMnNi and CrFeMnNiCu fillers. Sound welds without macro defects, such as internal pores or cracks, were obtained. The CoCrFeMnNi-based weld consisted of a face-centered cubic (FCC) structure, whereas the CrFeMnNiCu-based weld comprised (Co, Cr, Fe)-rich phase of FCC1 and a Cu-rich phase of FCC2 with the same FCC structure formed by phase separation. In the CrFeMnNiCu-based weld with a Cu-rich phase, the weld metal (WM) was stronger than that in the CoCrFeMnNi-based weld. The tensile fracture of all specimens occurred in the coarse-grained heat-affected zone (CGHAZ) at 298 K, while the tensile properties of the CrFeMnNiCu-based weld were improved compared to those of the CoCrFeMnNi-based weld, probably because the Cu-rich phase present in WM blocks the movement of dislocations. The WM of all tensile specimens at 77 K exhibited deformation twins, and deformation-induced martensitic transformation occurred in the BM and CGHAZ, showing improved strength and ductility compared to those at 298 K. Graphical Abstract