Phase Transformation Pathway in Additive Manufactured High-entropy Alloys

High-entropy alloys (HEAs) have garnered significant attention for their potential in delivering excellent mechanical performance. Additive manufacturing (AM), with its far-from-equilibrium solidification conditions, presents abundant opportunities to create materials with unique microstructures and properties. To harness the combined benefits of AM and HEAs, a fundamental understanding of the processing-structure-property relationship in additively manufactured HEAs is crucial yet challenging due to the complex phase selection and non-equilibrium solidification microstructures involved. In this study, we investigate the effect of solidification rate on the microstructure of laser additively manufactured eutectic HEAs. By varying the laser scan speed and hence the solidification rate, we reveal distinct solidification modes, including single-phase solidification, anomalous eutectic solidification, and coupled lamellar eutectic solidification. The resulting varied solidification microstructures and phase constituents lead to a wide range of mechanical properties. Thermodynamic modeling and atomistic simulations are performed to gain insights into the transition of solidification mode from coupled eutectic to anomalous eutectic and eventually to single-phase solidification as the solidification rate continuously increases. Our findings highlight that AM enables the development of multi-component alloys with tailored properties by offering a broad space for phase and microstructure design.