Twin‐Wire In Situ Additive Manufacturing of NiTiNb Eutectic Alloys: Eliminating Unmelted Nb Particles and Tailored Superelasticity

ABSTRACT A major challenge in fabricating eutectic NiTiNb alloys is the incomplete melting of Nb due to its much higher melting point than the NiTi matrix. In this work, a novel electron‐beam freeform additive manufacturing strategy is developed to eliminate unmelted Nb particles and achieve a fully eutectic structure through independent dual‐wire feeding with optimized process parameters. Specifically, NiTi and Nb wires are independently fed from opposite sides, with the Nb wire positioned beneath the NiTi wire. Precise control of wire spacing enables stable co‐droplet transfer into the molten pool guided by static analysis. Combined with enhanced beam energy density, unmelted Nb particles are effectively eliminated. Microstructural analysis revealed that higher Nb content promoted eutectic structure formation, and a fully eutectic structure is obtained through process optimization. At 90 mA, the (Nb 50.7 Ti) 85 Nb 15 alloy achieved 58.5% superelastic and 95.1% shape memory recovery. The eutectic structure suppresses the formation of martensitic wedge‐shaped structures and extensive stacking faults, thereby enhancing transformation reversibility. Moreover, recovery stress during reverse phase transformation partially restores the elasticity of the β‐Nb phase, further enhancing superelastic recovery. These results provide guidance for the in situ synthesized NiTiNb alloys with superior performance via additive manufacturing.