Achieving strength-ductility synergy in laser powder bed fused near-β titanium alloy via process optimization

Abstract

Laser powder bed fusion (LPBF) shows significant potential for fabricating dual-phase titanium alloys, but remains limited by the inherent strength-ductility trade-off arising from rapid solidification-induced cross-scale microstructural features. Overcoming these challenges requires precise process optimization to tailor microstructures and achieve synergistic enhancement of mechanical properties. This study systematically investigates the processing window and microstructure-property relationship in β-rich Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) alloy fabricated via LPBF, with an emphasis on elucidating the process-induced mechanisms governing strength and ductility. An optimal processing window was established, achieving near-full density (>99.0 %) and excellent surface quality (<11 μm), attributed to the controlled balance between melt pool lifetime and viscosity. Within this range, an exceptional strength-ductility synergy was realized, with an ultimate tensile strength of 903–925 MPa and an elongation of 15.4–27.4 %, alongside enhanced hardness (320.7–322.3 HV_0.2) and reduced friction coefficient (0.411–0.414). These superior mechanical properties originated from a hierarchical microstructure characterized by improved metallurgical bonding, refined grain features, and controlled dislocation density driven by precise thermal modulation. Temperature field simulation further revealed that variations in the temperature gradient, solidification rate and nucleation dynamics induced by laser processing significantly governed grain size and morphology, elucidating the underlying mechanisms of microstructural tailoring. This work demonstrates that the microstructure and properties of LPBF-processed Ti17 alloy can be effectively tailored through precise process parameters optimization, achieving remarkable forming quality and strength-ductility synergy.