Wall-Thickness-Dependent Microstructural Evolution and Mechanical Response of LPBF-Fabricated TA15 Titanium Alloy: The Role of Post-Solidification Cyclic Reheating

Wall thickness affects local heat accumulation during laser powder bed fusion (LPBF), but its role in governing the as-built martensitic morphology and tensile response of near-α TA15 alloy remains unclear. In this study, TA15 walls with thicknesses from 0.5 mm to 30 mm were fabricated under identical LPBF parameters. Optical microscopy, scanning electron microscopy, electron backscatter diffraction, tensile testing, fractography, and finite-element thermal simulation were used to correlate wall-thickness-dependent cyclic reheating with α′ lath evolution and mechanical behavior. Increasing wall thickness promoted α′ lath coarsening and the formation of colony-like lath structures with enlarged similarly oriented regions. The average α′ lath width increased from approximately 0.28 μm in the 0.5-T specimen to 1.55 μm in the 30-T specimen. The yield strength reached a maximum of 972.3 ± 5.29 MPa in the 1-T specimen, whereas elongation increased from 9.5 ± 0.6% to 17.8 ± 1.7% with increasing wall thickness. These results indicate a strong correlation between wall-thickness-dependent cyclic reheating, α′/α lath coarsening, lath-network evolution, and tensile-property variation in LPBF-fabricated TA15 alloy.