Directed Energy Deposition in Laser Additive Manufacturing (DED-LAM) enables the fabrication of complex 3D metal components but often results in textured columnar grains, residual stresses, and complex phase formations due to rapid solidification.[1] This study investigates the phase transformation mechanisms in CrMnNi TRIP steel during DED-LAM using in-situ X-ray diffraction (XRD) for real-time analysis.[2] Over 25,000 diffraction patterns were collected across 45 layers that provide high-resolution insight into microstructure evolution. A Python-based Pseudo-Voigt fitting model was optimized to extract peak parameters with high precision, enabling identification of key phases and tracking of transformation behaviour.

XRD heatmaps identified austenite (γ) as the dominant phase, stabilized by the alloy’s composition and the elevated temperatures. It also revealed the γ→ε→α′ transformation sequences that enable transformation-induced plasticity (TRIP) effects, enhancing the material’s strength and ductility.[3] Additionally, shifts in diffraction intensity traces indicated thermal strain accumulation, particularly near the component centre, suggesting significant thermal gradients and potential residual stresses.[4] Moreover, observed localized peak broadening pointed to fine-grained microstructures, providing valuable insights into the material’s strength and refinement. These findings provide insight into the thermal and transformation mechanisms active during DED-LAM and demonstrate the effectiveness of in-situ XRD for real-time microstructural characterization.

References

[1] S.-H., Li; et al. International Materials Reviews, 2023, 68(6), 605–647.

[2] T., Sun; et al. MRS Bulletin, 2020, 45(11), 927–933.

[3] M., Soleimani; A., Kalhor; H., Mirzadeh Materials Science and Engineering A, 2020, 795, 140023.

[4] S., Huang; et al. Frontiers in Metals and Alloys, 2022, 1, —.