Fig. 1. Schematic illustration of (a) the challenges in qualifying the mechanical properties of geometrically complex AM components, i.e., Inconel 718 blade integrated disks manufactured using L-PBF, (b) geometrical dimensions of mechanical test specimens excised from the XZ plane of a large block (dimensions in mm) and the applied scanning strategy.

Fig. 2. EBSD orientation maps in the (a) XY and (b) XZ planes of SLM Inconel 718 specimen, inset in (b) schematically showing the “microstructure unit”, pole figures in the XY plane of the (c) cylindrical-shaped grains and (d) plate-shaped grains shown in (a).

Fig. 3. Pole figures taken in the XY plane of SLM Inconel 718 specimens with different values of t/d.

Fig. 4. (a) TEM bright-field image showing the morphology and orientation of solidification cells and needle-shaped δ phases, the insets showing the SAED patterns of γ phase and δ phase, (b) TEM bright-field image showing the γ′′ phases in HA-treated specimen, the insets showing the orientation relationship between γ and γ′′phases, a sketch showing the dimension of thickness and diameter of γ′′ phases.

Fig. 5. (a) Tensile engineering stress-strain curves of the SLM Inconel 718 specimens with t/d ranging from 8.3 to 0.8 after HA treatment, (b) evolution of the yield strength and ultimate tensile strength with reducing t/d, (c) evolution of the total elongation (εte), uniform elongation (εue) and post-necking elongation (εpe) with reducing t/d.

Fig. 6. (a) Total elongation plotted against L/S1/2 and fitted by Oliver's formula (black dashed line), (b) true stress-true strain curves and the corresponding K-M strain hardening rate curves of SLM Inconel 718 with varying t/d.

Fig. 7. (a) Contour maps of the major strain at the front surface of gage section of t/d ≥ 2.0 specimens at εg = 10% and t/d = 0.8 specimen at εg = 2.6%, the blank areas in the contour maps result from the localized fracture of the white and black dot pattern when subjected to large strain, (b) line profiles of the major strain over εg along the center line of gage section.

Fig. 8. SEM surface tensile damage and fracture morphologies of the t/d = 4.2 specimen in the (a) low and (b) high magnifications, SEM surface tensile damage and fracture morphologies of the t/d = 2.0 specimen in the (c) low and (d) high magnifications, (e) SEM surface tensile damage and fracture morphologies of the t/d = 0.8 specimen.

Fig. 9. Stress amplitudes versus the number of cycles to failure (S-N) curves of SLM Inconel 718 specimens with t/d ranging from 8.3 to 0.8.

Fig. 10. SEM micrographs of fatigue fracture surfaces of the t/d = 6.3 specimen at (a) σa = 396 MPa and (b) σa = 279 MPa, the right and left insets in (a) showing the crack initiation site and crack propagation area, respectively, inset in (b) showing the crack initiation site, SEM micrographs of fatigue fracture surfaces of the t/d = 0.8 specimen at (c) σa = 396 MPa and (d) σa = 279 MPa, inset in (c) showing the crack initiation site, (e) crack propagation area of the t/d = 0.8 specimen at σa = 396 MPa.

Fig. 11. (a) Summary of the normalized yield strengths of conventionally-fabricated pure metals (polycrystalline Cu [43] and Ni [40]) and engineering alloys (CA6NM martensite stainless steel [45] and Ti alloy [41]) as well as the SLM Inconel 718 as a function of t/d, (b) schematic illustrations of contributions of the surface and interior grain layers to the yield strength, (c) the predicted yield strength map of polycrystalline Cu as a function of d and t/d.

Fig. 12. Postmortem TEM observations on the dislocation structure (a) at the surface and (b) in the center of the t/d = 0.8 specimen.

Fig. 13. (a) EBSD orientation map of the “microstructure unit” showing a large misorientation between the cylindrical- and plate-shaped grains, (b) the corresponding GROD map at εg = 4.85% showing the strain gradient within the “microstructure unit” (indicated by the blue arrows), (c) the corresponding GND density distribution map at εg = 4.85% showing pronounced GNDs adjacent to the “microstructure unit” interface (indicated by the black arrows), (d) line profile of GND density distribution along red line shown in (c).

Fig. 14. (a) EBSD orientation map and the corresponding (b) Taylor factor mapping, (c) KAM mapping of the type II (t/d = 0.8) specimen close to the tensile fracture.

Fig. 15. Summary of the normalized fatigue limits (at 1 × 107 cycles) of SLM Inconel 718 and conventionally-fabricated Ti alloy [41], CA6NM martensite stainless steel [45], Cu [36,[79], [80], [81], [82], [83], [84]] as a function of specimen thickness.