Energy input effects on the microstructure and mechanical behavior of Ti–Nb alloy additivelymanufactured by electron beam melting

Abstract

The critical niobium content required to maintain the β phase in additively manufactured Ti–Nb alloys, preventing martensitic transformation, is still unclear. Our previous study showed that 42 wt% Nb was insufficient. Therefore, in this study, new pre-alloyed β-titanium alloys with high niobium percentage (56 wt%, Ti–56Nb) were successfully produced by Electron Beam Powder Bed Fusion (PBF-EB), and the effect of varying beam current (4 mA, 5 mA, and 7 mA) on microstructure and mechanical properties was studied. All processing regimes achieved proper fusion, with a uniform porosity distribution (∼0.3 %) and minimal niobium-enriched regions, attributed to powder heterogeneity. Beam current variations significantly affected melt pool dynamics, phase constitution, and heat distribution. Planar growth along layer boundaries and cellular structures within melt pools was observed, caused by high thermal gradients and high cooling rates. Texture analysis revealed that higher beam currents induced fiber-like textures due to zigzag beam movement and deep remelting, while 4 mA and 5 mA beam currents produced biaxial textures with minimal fiber contributions. TEM analysis indicated that higher energy input facilitated martensitic transformation, whereas lower energy enhanced β-phase stabilization. Mechanical testing identified the 4 mA regime as optimal, achieving the highest yield strength, favorable β-phase fraction, reduced elastic modulus, and enhanced wear resistance. This study demonstrates how varying beam energy inputs during PBF-EB printing can tailor the meso- and micro-scale structure and mechanical properties of Ti–56Nb alloys, providing valuable insights for optimizing densification, microstructure, texture, and mechanical performance in additive manufacturing applications.