Strengthening mechanism transition via shape-preserving thermomechanical treatment of defect-dominated pure Ti fabricated by PBF-LB

Abstract

This study investigates the effect of direct hot isostatic pressing (HIP) on the microstructure, and mechanical properties of pure titanium (Ti) components fabricated by laser-based powder bed fusion (PBF-LB). Specimens were produced under fully melted conditions using optimized PBF-LB parameters and subsequently subjected to a thermo-mechanical HIP process over a wide temperature range (390-790 degrees C, 2000 bar, 2 h). In the As-Built condition, rapid solidification resulted in an acicular alpha ' martensitic microstructure with high residual stress (similar to 560 MPa), near full density (99.998 %), and mechanical properties of 717.2 MPa tensile strength (TS), 635.3 MPa yield strength (YS), and 20.2 % elongation. With increasing HIP temperature, residual stress and internal defects were progressively reduced, accompanied by microstructural evolution through recovery, recrystallization, and grain coarsening. Notably, under the HIP 590 degrees C condition, pressure-assisted deformation promoted effective grain refinement while preserving a high dislocation density. As a result, the material retained its As-Built strength (TS approximate to 709 MPa, YS approximate to 631 MPa) while exhibiting enhanced ductility (23.0 %). Overall, the results reveal a clear transition from an unstable strengthening mechanism in the As-Built condition dominated by acicular martensite and residual stress to a stable strengthening mechanism induced by direct HIP processing, characterized by effective grain refinement and a maintained high dislocation density. These findings demonstrate that direct HIP is an efficient and effective post processing route to produce dense, stress relieved, and mechanically stable pure Ti components, significantly expanding the applicability of PBF-LB fabricated pure Ti in biomedical, aerospace, and high performance structural applications.