Additive Manufacturing of a Strong and Ductile Oxygen-doped NbTiZr Medium-Entropy Alloy

Abstract Refractory multi-principal element alloys (RMPEAs) are distingushed by their single-phase solid solutions, predominantly featuring body-centered cubic (BCC) structures and composed of multiple refractory elements in near-equiatomic proportions. These compositions offer exceptional mechanical properties. Recent advancements in additive manufacturing (AM) techniques have created new opportunities for optimizing the microstructures of RMPEAs, resulting in enhanced mechanical properties. This study aims to fabricate a high-quality oxygen-doped NbTiZr alloys using laser powder bed fusion (L-PBF) and investigate their microstructure and mechanical properties. Our analysis reveals refined grain sizes and a periodic combination of fine near-equiaxed and columnar grain morphologies in the AM-fabricated alloy. Its substructure is characterized by the coexistence of loosely defined cellular dislocation networks and elemental segregation. Compared to its cast counterpart, the additively manufactured alloy exhibits a combination of high yield strength, excellent tensile ductility, and enhanced work hardening. These attributes make the AM-fabricated oxygen-doped NbTiZr alloy a promising candidate for applications required balanced mechanical properties. Understanding the specific effects of different crystal structures and deformation mechanisms is essential for optimizing AM processes to tailor the microstructure and achieve the desired mechanical performance in various engineering applications.