Achieving complete columnar-to-equiaxed transition in laser-processed AlCoCrFeNi alloys via mixed powder preparation

The columnar-to-equiaxed transition (CET) is critical for mitigating microstructural anisotropy and intergranular cracking associated with columnar grains in laser-processed alloys. Here, a complete CET was achieved in an AlCoCrFeNi high-entropy alloy using mechanically mixed powders, resulting in more than an order-of-magnitude grain refinement compared with that prepared from pre-alloyed powder. The CET is attributed to liquid-phase undercooling induced by constitutional fluctuations. In this framework, a local inversion of the chemical profile (relative to the normal segregation pattern) ahead of the solid–liquid interface reduces the local liquidus temperature, favoring nucleation over growth, even under the steep thermal gradients inherent to laser processing. While direct observation of liquid compositional fluctuations is not feasible, the proposed mechanism provides a physically consistent explanation for the experimental observations. These findings suggest a new pathway for microstructural control in laser processing, where engineered compositional fluctuations may be exploited to tailor grain structures in multicomponent alloys.