In‐Situ Construction of Multi‐Scale Heterogeneous Structures in L‐DED IN718 Coatings via WMoTaNb Incorporation for Enhanced Strength‐Toughness Synergy

ABSTRACT

To improve the strength–toughness balance of IN718, and alleviate the brittleness commonly associated with refractory high‐entropy alloys, this study proposes a novel strategy to fabricate defect‐free IN718/WMoTaNb heterogeneous multiprincipal element alloy coatings via laser‐directed energy deposition. The incorporation of WMoTaNb elements significantly altered the solidification pathway of the IN718 matrix, triggering the in‐situ formation of a unique tri‐phase structure consisting of an FCC matrix, refractory‐rich BCC phases, and an HCP‐structured intermetallic phase. By systematically optimizing the laser processing parameters, the volume fraction and morphological distribution of these constituent phases were controlled precisely. Microstructural analysis indicates that the high‐density dislocations and the strengthening provided by the BCC and an HCP‐structured intermetallic phase play a critical role in the material's reinforcement. The developed coating achieved a peak microhardness of 634.8 HV (120% improvement over monolithic IN718) and a 13.95% increase in 650°C flexural toughness, breaking the traditional strength–toughness trade‐off. This work provides a new paradigm for designing high‐performance high‐temperature coatings by integrating superalloys with refractory high‐entropy systems.