Residual Stress Relaxation After Aging Heat Treatment in Laser Powder Bed Fusion CM247LC Superalloy Parts Quantified by Neutron-Diffraction-Validated Full-Field Eigenstrain Tomography

Residual stresses generated during laser powder bed fusion (LPBF) can compromise dimensional stability and in-service performance of nickel-based superalloy components, while the quantitative assessment of stress relaxation during post-build heat treatment remains challenging in three dimensions. This paper quantifies the effects of an aging treatment at 900 °C for 8 h on the residual stress and eigenstrain distributions in an LPBF-fabricated CM247LC component. Eigenstrain tomography is used to reconstruct full-field three-dimensional distributions of eigenstrain, residual elastic strain, and residual stress tensors from synchrotron X-ray diffraction measurements of a single residual elastic strain component acquired from only two orthogonal projections. Reconstruction accuracy is independently validated using neutron diffraction strain measurements. The results show substantial residual-stress relaxation after aging, including a marked reduction in the magnitude of all residual stress tensor components across the volume. Statistical analysis of the raw diffraction data demonstrates a pronounced homogenisation of internal macroscopic strains, accompanied by a corresponding decrease in reconstructed eigenstrain components toward near-zero values. Leveraging a highly streamlined two-projection tomographic protocol, these findings quantitatively reveal the three-dimensional mechanics of macroscopic (Type I) stress relaxation without the need for exhaustive experimental beamtime. The results provide critical volumetric data linking thermal exposure to the elimination of distortion-driving eigenstrain gradients. Ultimately, this work represents a significant advancement in additive manufacturing process evaluation, establishing this efficient tomographic framework as a practical, non-destructive tool for optimizing post-build heat treatments and ensuring dimensional stability in complex additively manufactured superalloys.