Dilution-induced compositional transformation and mechanical degradation in multi-material directed energy deposition

Multi-material additive manufacturing enables the integration of dissimilar materials to create heterostructured materials with multifunctional properties. In this work, strong maraging steel and ductile medium-entropy alloy were alternately deposited using directed energy deposition (DED) with a 2000 W infrared fiber laser featuring top-hat energy distribution, aiming at combining high strength and ductility. However, despite defect-free interfaces, the resulting layered structures exhibited lower strength and hardness than both base alloys. Extensive elemental mixing from melt pool dilution resulted in unintended in-situ alloying, phase suppression, and mechanical degradation. This work highlights the importance of evaluating dilution-driven compositional shifts in multi-material DED design.