Thermal-History-Mediated Defect-Microstructure-Property Evolution in Multi-Laser Powder Bed Fusion of TC11 Titanium...

Multi-laser powder bed fusion (PBF-ML) enables efficient fabrication of large components but introduces spatially heterogeneous thermal histories near inter-laser overlap zones. However, how global thermal-input variables and local thermal-path variations jointly affect defect evolution, microstructure, and mechanical response in geometrically constrained Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) structures remains unclear. Here, TC11 arch structures were fabricated by varying laser power, scanning speed, overlap-zone position, and interlayer rotation and characterized by tensile testing, optical metallography, Scanning Electron Microscope (SEM), and fractography. Increasing laser power from 170 to 290 W increased Yield Strength (YS) and Ultimate Tensile Strength (UTS) from 955 and 1228 MPa to 1259 and 1463 MPa, respectively, while Elongation (EL) decreased from 14.7% to 3.1%. Increasing the scanning speed from 1050 to 1450 mm/s produced the opposite strength-ductility trend, whereas overlap-zone position had limited influence on strength and 67° interlayer rotation produced moderate improvements. Defect count and area fraction did not always vary synchronously, while semi-quantitative SEM analysis revealed microstructural coarsening with increasing laser power and refinement with increasing scanning speed. These results show that global thermal-input variables primarily govern the overall strength-ductility and microstructural-scale responses, whereas local thermal-path variables mainly regulate spatial defects and microstructural heterogeneity.