Residual stress evolution and post-annealing relaxation in LPBF-fabricated TA15 titanium alloy

Laser powder bed fusion (LPBF) is a promising route for fabricating lightweight, high-strength TA15 titanium alloy components for aerospace applications. However, the severe thermal cycling inherent to the process leads to substantial residual stress accumulation, plastic strain buildup, and distortion, which compromise dimensional accuracy and structural reliability. In this study, a thermo-mechanically coupled finite element framework was developed to investigate residual stress evolution in LPBF-fabricated TA15 bridge structures, with particular emphasis on stress relaxation during post-annealing treatment (PAT). The model was validated against experimentally measured warpage after support removal using 3D scanning, showing good predictive capability. Based on the validated framework, the evolution of plastic strain and residual stress during layer-by-layer deposition was analyzed, revealing that residual stress buildup is dominated by constrained thermal contraction and cyclic plastic deformation. During subsequent PAT, stress relaxation is suggested by the simulations to occur mainly through temperature-activated plastic strain redistribution rather than purely elastic recovery. Systematic parametric analyses further clarified the coupled effects of annealing temperature and dwell time on stress homogenization and distortion reduction, from which a PAT process map was established for efficient post-process optimization. Microstructural characterization and tensile testing further showed that a suitable annealing window can substantially relieve residual stress while maintaining a favorable balance between strength and ductility. More importantly, by analyzing the full LPBF-PAT-support removal process chain within a unified thermo-mechanical framework, the present work clarifies the intrinsic linkage between stress accumulation during fabrication, stress redistribution during post-annealing, and distortion release after cutting. This process-chain perspective provides mechanistic insight into residual stress evolution and relaxation in LPBF-fabricated TA15 components, and offers a physics-informed basis for optimizing post-annealing conditions in aerospace additive manufacturing.