Tailoring Differentiated Multiscale Microstructure to Enhance the Mechanical Properties of Additively Manufactured AlCoFeNi ₂ at Room and High Temperatures via Annealing

ABSTRACT Additively manufactured AlCoFeNi series eutectic high‐entropy alloys (EHEAs) exhibit nonequilibrium dual‐phase microstructure in the as‐printed state, allowing them to be easily tailored through annealing to explore their strength–toughness potential. In this study, we investigated the microstructural evolution after annealing and the room‐temperature/650°C tensile mechanical properties of a laser powder bed fusion‐fabricated AlCoFeNi 2 EHEA. The annealing treatment was found to induce changes in hierarchical microstructural parameters, including residual dislocation density, lamellar structure spacing, dual‐phase fraction, and grain size. These parameters showed monotonic relationships with annealing temperatures, except for grain size, due to the transformation from grain coarsening to recrystallization when the annealing temperature increased to 900°C. Our results indicated the difference in the deformation micromechanism at room temperature and 650°C. Dislocation slip dominated during room temperature deformation, with the phase boundaries effectively impeding dislocation motion, while stacking faults and twins were activated at 650°C, with grain boundaries and phase boundaries contributing to strengthening. This necessitated that multiscale microstructure tailoring had to be differentiated to handle room temperature or 650°C conditions. After optimal heat treatment, we doubled the ductility value compared with the as‐printed state while preserving the substantial as‐printed strength under the two temperature conditions. This work also preliminarily analyzed the contribution levels of structural features at different scales to strength via quantitative modeling, further confirming the significant microstructural tunability of additively manufactured eutectic high‐entropy alloys and providing a basis for differentiated microstructure tailoring for specific service temperatures.