Fig. 1. (a) SEM image showing R108 powder morphology. (b) Cumulative particle size distribution of R108 powder. Both R65 and R108 had similar powder morphologies and particle size distributions.

Fig. 2. CAD model of a printed plate with the three thin-wall parts. In (a) 3D view and (b) top view showing thin-wall parts with thicknesses of 5 mm, 1 mm, and 0.25 mm, respectively. The red box in (b) highlights the 5 mm thick part with a corresponding close-up image shown as an inset. Blue arrows indicate a bidirectional scan strategy at a hatch angle of 15° with respect to the part thickness, employed for all the thin-wall samples. The laser was scanned at a 45° angle with respect to the recoating direction (top right).

Fig. 3. (a) As-built LPBF R108 thin-wall parts arranged in order of increasing thicknesses (0.25 mm, 1 mm, 5 mm) from left to right. The red dashed line shows the variation in LBH for each part. (b) Example of a specimen taken from the center region of a 1 mm sample for metallurgical studies.

Fig. 4. Image analysis process for crack quantification of R65 thin-wall samples. The red dots in the processed image indicate cracks identified by ImageJ.

Fig. 5. FE model geometry and mesh of thin-wall structure printed on the substrate. Mesh size is refined for the printed wall and coarse for the substrate.

Fig. 6. (a) Effect of part thickness on the LBH of 3D-printed thin-wall parts. The intended build height for the printed features was 50 mm. Two parts were built for each alloy. (b) Effect of part thickness on the crack area fraction.

Fig. 7. Internal micro-cracks along BD in 5 mm thick (a) R65 and (b) R108 thin-wall parts.

Fig. 8. Simulated Von Mises stress distribution in fully printed LPBF thin-walled structures with varying thicknesses (a) 0.25 mm, (b) 1 mm, and (c) 5 mm. Thicknesses lower than 5 mm show LBH.

Fig. 9. (a) 3D cross-section of a thin-wall part taken from the middle of the Y axis showing center and edge dashed lines used for extraction of stress data. (b) Cross-section of the XZ plane showing the locations of the extracted stresses and demonstrating symmetrical stress distribution in the 5 mm thin-wall part.

Fig. 10. Simulated stresses of thin-wall parts with different thicknesses extracted at (a, c, e) the edge and (b, d, f) the center. Stress distributions are organized as follows: (a, b) Von Mises stresses; (c, d) stresses in Z direction; (e, f) stresses in Y direction. The inset in (d) shows close-up of the compressive stresses observed in the final layers for the thinner 0.25 mm and 1 mm parts. The stress distributions were taken at different positions along the build direction as shown in Fig. 9.

Fig. 11. Top surface SEM micrographs of 0.25 mm thick R65 as-built thin-wall part indicating (a) a lack of fusion zone and (b) track irregularity surrounded by dendritic features showing material solidification.

Fig. 12. Stress distribution in the X-Y plane of the last layers taken at 6 mm build height. It corresponds to the inset region in Fig. 10(d). The red and blue colors highlight regions undergoing compressive and tensile stresses, respectively.

Fig. 13. Maximum part displacement along the X (part thickness) direction as a function of the position along with the unrestricted part height (see Fig. 12 for reference axes). Three different part thicknesses (0.25 mm, 1 mm, and 5 mm) are compared here. The experimental LBH values are also marked using dashed lines.

Fig. 14. Part distortion observed in the R65-0.25 mm thin-wall part in (a) as-printed and (b) simulated conditions.

Fig. 15. Schematic demonstrating the mechanism associated with limiting build height in thin-wall parts. Thinner parts like (a) are more sensitive to displacement in X compared to thicker parts like (b)—4X thicker than (a).