Laser powder bed fusion of Al-Doped CoCrNi Medium Entropy Alloy: Microstructural mechanisms imparting high strength-ductility synergy

The Al8(CoCrNi)92 medium entropy alloy (MEA) was successfully fabricated using the laser powder bed fusion (LPBF) technique. Process optimization through orthogonal experiments identified the optimal parameters—scanning distance of 100 μm, laser power of 180 W, and scanning speed of 500 mm/s—resulting in a high relative density of 99.28 %. The as-printed alloy exhibited a hierarchical heterogeneous microstructure comprising coarse and fine grains, cellular substructures, and nanoscale L12 precipitates. These features synergistically enhanced mechanical properties, yielding a tensile strength of 872 MPa, a yield strength of 568 MPa, and a fracture elongation of 24.6 %. Microstructural characterization and molecular dynamics simulations revealed deformation mechanisms are dominated by dislocation slip, stacking faults, and Lomer-Cottrell locks. This work highlights the potential of LPBF and compositional tailoring to design high-performance structural materials, offering new insights into achieving an optimal balance of strength and ductility through hierarchical heterogeneous structures.