Rapid solidification microstructure evolution behavior of AlCoCrFeNi_2.1 eutectic high-entropy alloys fabricated by laser powder-bed fusion

Establishing the correlation between the solidification microstructure and processing conditions has long been a fundamental prerequisite for achieving the desired properties, which requires an in-depth understanding of the specific material. In this work, the rapid solidification microstructure evolution of AlCoCrFeNi_2.1 eutectic high-entropy alloy (EHEA) fabricated by laser powder-bed fusion was experimentally studied. Moreover, a single-track temperature field model was developed to capture the temporal and spatial variations in thermal gradient and solidification rate at the liquid-solid interface. The as-built AlCoCrFeNi_2.1 EHEA featured several-micrometer eutectic colonies with ultra-fine lamellar structure inside. Through adjusting the scanning speed, the morphology of eutectic colonies transitioned from elongated to equiaxed, while the lamellar eutectic remained largely unchanged. By integrating experimental data with simulation results, a solidification map was established to describe the columnar-to-equiaxed transition (CET) behavior within the melt pool. The results showed that as the scanning speed increased from 550 to 1500 mm/s, a more pronounced CET trend was attributed to a reduced thermal gradient and a decrease in the ratio of thermal gradient to solidification rate. The good match between the experiments and simulations confirms the reliability of the solidification map. The relationship between process parameters, solidification conditions, and solidification structure can be effectively obtained.