Improved corrosion resistance of laser directed energy deposited AlCoCrFeNi_2.1 eutectic high-entropy alloy via microstructure and residual stress control

In this study, AlCoCrFeNi_2.1 eutectic high-entropy alloys (EHEAs) were fabricated via laser directed energy deposition (LDED) to investigate the synergistic effects of microstructural evolution and residual stress on corrosion behavior in 0.6 M NaCl solution. The results revealed that LDED process significantly refined the eutectic lamellae and redistributed alloying elements, leading to a more homogeneous dual-phase (FCC + BCC) microstructure compared with the cast sample. Increasing the volumetric energy density (VED) promoted a higher FCC phase fraction. Notably, the compressive residual stress initially increased and then decreased, reaching a peak magnitude of 101.86 MPa at a VED of 218 J·mm⁻³. Electrochemical measurements demonstrated that the VED 218 sample exhibited the lowest corrosion current density (1.35 × 10⁻⁷ A·cm⁻²) and the widest passive potential range (469.56 mV). X-ray photoelectron spectroscopy analysis confirmed that, compared to the cast sample, the LDED-fabricated samples possessed a Cr-enriched passive film with a higher Cr_ox³⁺ fraction. Mott-Schottky results further indicated a lower carrier concentration for the LDED-fabricated samples, suggesting the formation of a denser and more stable passive film. The improved corrosion resistance was attributed to two synergistic mechanisms: (i) microstructural refinement and compositional homogenization reduced micro-galvanic potential differences, and (ii) the tailored compressive residual stress suppressed point-defect generation, thereby stabilizing the passive film. Overall, LDED processing provides an effective strategy for tailoring the microstructure and residual stress of EHEAs to achieve enhanced corrosion resistance in chloride-containing environments.