Microstructural and Mechanical Characteristics of Welded CoCrNi‐Based Medium Entropy Alloys

Medium entropy alloys (MEAs), consisting of two to four principal elements in near‐equiatomic ratios, are emerging materials with excellent strength, ductility, toughness, and corrosion resistance, particularly under cryogenic and high‐temperature conditions. Reliable welding of MEAs is essential for their industrial deployment, yet their unique metallurgical features such as low stacking fault energy and sluggish diffusion pose distinct challenges. This review summarizes recent advances in MEA welding, covering both fusion‐based processes (GTAW, LBW, and EBW) and solid‐state methods (friction stir welding and diffusion bonding). Optimized friction stir welding can produce grain refinement of about 60%–80%, low heat‐input laser/electron beam welding can retain about 90%–95% of base‐metal tensile strength, and ultrasonic‐assisted laser welding has been reported to improve ductility and fatigue resistance by about 30% through porosity suppression and grain refinement. Dissimilar welding with steels and Ni‐based alloys highlights interfacial issues such as intermetallic formation, mitigated partly by interlayers. Modeling and machine learning are emerging tools for predicting weld quality and performance. Remaining challenges include segregation control, HAZ optimization, scalability, and standardized testing, which must be addressed to enable widespread industrial adoption.