Microstructure Tailoring of Laser Powder Bed Fused Nb521 Alloy Toward Strength‐Ductility Synergy

ABSTRACT

Niobium‐based refractory alloys are promising candidates for high‐temperature aerospace structures, yet their limited ambient‐temperature ductility and poor processability remain major barriers to broader implementation. Here, Nb521 alloy was fabricated by laser powder bed fusion (LPBF), and the effects of processing conditions and subsequent hot isostatic pressing (HIP) on microstructural development and mechanical response were systematically examined. The as‐printed alloy exhibited a heterogeneous grain structure composed of columnar and equiaxed grains, together with pronounced solute segregation and dense dislocation substructures generated by rapid solidification. HIP promoted chemical homogenization, reduced the fraction of low‐angle grain boundaries, weakened the crystallographic texture, and induced a partial tetragonal‐to‐monoclinic transformation of dispersed ZrO ₂ particles. These microstructural modifications led to a marked improvement in the strength‐ductility balance. In particular, after HIP treatment, the specimen fabricated with a laser power of 240 W and a scanning speed of 500 mm s ⁻¹ (LED = 480 J m ⁻¹ ) exhibited an ultimate tensile strength of 581.9 ± 2.98 MPa, a yield strength of 442.2 ± 8.66 MPa, and a tensile elongation of 22.3% ± 0.62%. Quantitative strengthening analysis indicates that the yield strength arises from the combined contributions of lattice friction, grain‐boundary strengthening, dislocation strengthening, and precipitation strengthening. The precipitation contribution is governed predominantly by Orowan bypassing, with an additional contribution from particle shearing, enabling simultaneous strengthening and ductility retention. These findings clarify the microstructural origins of the enhanced mechanical performance of LPBF‐processed Nb521 alloy and provide guidance for designing additively manufactured niobium‐based alloys with improved strength‐ductility synergy.