Enhanced strength - Ductility synergy in laser direct energy deposited Al-Cr-Fe-Ni multi-principal element alloy via interlayer pause strategy

Laser direct energy deposition (L-DED) serves as an advanced near-net-shaping technique for fabricating complex metallic structural components. However, complex thermal histories and epitaxial growth characteristics inherent to L-DED processes cause microstructural coarsening and anisotropy, leading to significant property heterogeneity. This work introduces an interlayer pause strategy (with pause durations ranging from 60 to 300 s) to mitigate heat accumulation during layer-by-layer deposition by optimizing molten pool thermal profiles, thereby refining as-printed microstructures and enhancing vertical structural homogeneity. The processed alloy exhibits kinked FCC substructures at sub-micron scales alongside decomposed BCC/B2 nanostructures. This unique multiscale architecture overcomes strength-ductility trade-offs and enabling remarkably low mechanical anisotropy. Specimens fabricated with the optimal interlayer pause condition (∼180 s) demonstrate further enhanced mechanical properties, achieving ultimate tensile strengths exceeding 1.43 GPa while maintaining ductilities ≥18 %. This approach provides a straightforward yet effective solution for controlling complex thermal histories in laser-based multilayer deposition.