Microstructural evolution, mechanical properties, and corrosion behavior of dissimilar gas metal arc welded (GMAW) CoCrFeMnNi high entropy alloy and 304 stainless steel using ER316L filler metal

• First report on GMAW of CoCrFeMnNi HEA to 304 stainless steel using ER316L Mo-bearing filler wire. • The similar HEA joint showed the best performance due to sluggish diffusion effect. • Dissimilar low heat input joint yields fusion zone with 89% FCC and superior joint strength. • High heat input in dissimilar joint causes excessive Mo dilution, promoting brittle BCC/sigma. • High heat input enhances corrosion resistance due to Mo-enrichment and lower grain boundaries. The current study investigates the microstructural evolution, mechanical properties, and corrosion behavior of dissimilar gas metal arc welds between CoCrFeMnNi high-entropy alloy (HEA) and AISI 304 stainless steel using a ER316L filler metal, with a focus on the effect of heat input (0.19 kJ/mm vs. 0.40 kJ/mm). The similar HEA/HEA reference joint demonstrated superior properties with a single-phase FCC microstructure, a strength of 635 MPa, and the lowest corrosion rate of 0.0006 mm/year due to sluggish diffusion effect. For the HEA/304 SS dissimilar joints, the low heat input joint exhibited a fusion zone (FZ) with 89.3% FCC and 10.7% BCC phase, a tensile strength of 558 MPa, and a corrosion rate of 0.0013 mm/year. In contrast, the high heat input joint resulted in excessive filler metal dilution, increasing the Mo content to 20.48 wt.% and drastically altering the FZ microstructure to 64.4% FCC and 35.4% BCC, alongside the formation of brittle sigma intermetallic and Co 0.72 Fe 0.28 ordered phases. This led to a reduction in tensile strength to 523 MPa, though ductility increased to 4.8%, and corrosion rate to 0.001 mm/year. Both dissimilar joints fractured in the softer HEA base metal, confirming the integrity of the weld region. The results establish that the low heat input preserves a more favorable microstructure, however, the high heat input promotes deleterious phase formation (BCC + Sigma), critically degrading the joint's mechanical properties. However, the Mo-enrichment and more grain boundaries are detected as the major factors for enhancing the corrosion resistance at the higher heat input.