Relationship Between Processing, Microstructure and Property in the Ti-20Nb-6Ta Alloy Fabricated by Laser Powder Bed Fusion

Abstract Laser powder bed fusion (LPBF) enables the fabrication of titanium alloys with tailored microstructures that allow for control of their properties. In this study, the Ti-20Nb-6Ta alloy was processed by LPBF under various manufacturing conditions. The volumetric energy densities (VED) ranged from 66.1 to 175.8 J/mm 3 and bidirectional scanning with rotation angles of 0° and 90°. Optical microscopy revealed distinct melt pool morphologies and track interaction effects depending on hatch spacing with reduced geometric continuity was observed at higher energy densities. X-ray diffraction (XRD) combined with Rietveld refinement showed that the microstructure was predominantly orthorhombic α″-Ti martensite (72.9-90.7 wt.%), with smaller amounts of α′-Ti martensite (3.8-16.9 wt.%) and retained β-Ti (4.0-10.2 wt.%). Electron backscatter diffraction (EBSD) analysis revealed that the low-energy condition (VED66/ROT90) had the highest proportion of low-angle grain boundaries (35.8%), indicating pronounced martensitic substructuring. Conversely, the high-energy condition (VED175/ROT90) exhibited a reduced fraction of low-angle boundaries (~ 6%) and a higher fraction of high-angle boundaries. Pole figure analysis revealed a more defined crystallographic texture in the high-energy condition. Reconstruction of the β parent phase confirmed that this anisotropy is inherited from the solidification-controlled β texture and is then transferred to the martensitic structure through orientation inheritance during the β-Ti → α″-Ti martensite transformation. Compression tests revealed that increasing the VED resulted in an increase in the apparent elastic modulus from 9.6 to 17.5 ± 2.1 GPa, as well as an increase in the compressive yield strength from 647 ± 53 to 818 ± 42 MPa. Similarly, Vickers hardness increased from approximately 208 to 263 ± 29 HV 0.1 . These improvements correlate with the evolution of phase constitution and crystallographic texture, as revealed by Rietveld refinement and EBSD. Electrochemical tests in a phosphate-buffered saline (PBS) solution demonstrated stable passive behavior for all processing conditions, with similar passive current densities and no evidence of localized corrosion up to 3 V versus Ag/AgCl. These results indicate that the investigated LPBF processing conditions exhibited similar passive electrochemical behavior despite the observed microstructural variations.