Challenges and opportunities in additive manufacturing of high entropy alloys

High entropy alloys (HEAs) are a class of multi-principal element alloys that exhibit promising properties for structural and functional applications. Additive manufacturing (AM) techniques provide a pathway for fabricating HEAs with complex geometries and tailored compositions. This paper reviews the recent progress in developing HEAs using laser-based (directed energy deposition, laser powder bed fusion) and electron beam-based (electron beam powder bed fusion) AM processes. A wide range of HEAs, including CoCrFeMnNi, AlxCoCrFeNi, refractory HEAs, and interstitial-solute hardened HEAs, have been fabricated through AM of gas/water atomized powders or elemental powder blends. Processing parameters such as laser power, scan speed, and hatch distance significantly influence the microstructure, phases, and defects in laser-based AM-printed HEAs. Rapid solidification during AM suppresses phase segregation and elemental partitioning, leading to refined microstructures with enhanced mechanical properties compared to cast counterparts. Post-treatments, including annealing, hot isostatic pressing, and laser shock peening, reduce residual stresses and porosities in AM-printed HEAs. Future opportunities lie in developing compositionally graded, dual-phase, and composite HEAs through AM to optimize properties further. Standardized models are needed to predict optimized AM parameters for defect-free printing of new HEAs.