Investigation of microstructural evolution at the melt pool interface in AlCoCrFeNi_2.1 high-entropy alloy fabricated by laser-directed energy deposition

Abstract To clarify the effect of melt pool dilution behavior on the microstructural evolution of high-entropy alloys during laser-directed energy deposition, this study investigates the deposition of AlCoCrFeNi 2.1 on a 304L substrate. The optimal process parameters were determined as a laser power of P = 900 W and a scanning speed of v = 500 mm/min. Experimental results indicate that three distinct microstructures—planar crystals, columnar crystals, and eutectic structures—are present at the interface between the substrate and the deposited layer. The Fe element concentration decreases from the substrate to the eutectic region and stabilizes in the eutectic region at C Fe = 16.3 %. The growth direction of the columnar crystals aligns with the temperature gradient in the melt pool, and Fe is primarily enriched within these columnar structures. During laser-directed energy deposition, the microstructural evolution within the melt pool mainly occurs in the initial deposition layer. In the subsequent stable deposition process, a uniform eutectic microstructure is consistently observed, demonstrating that the influence of dilution is primarily concentrated in the initial deposition stage.