Fig. 1. Schematics of (a) LPBF-0° where the tensile and build directions are parallel, (b) LPBF-90° where the build direction is perpendicular to the tensile direction, and (c) stripe scanning strategy with the stripe size of 5 mm (the arrows are laser tracks).

Fig. 2. (a) IPF-Y map, with Y being the build direction, (b) band contrast (BC) map, and (c) grain misorientation angle distributions in LPBF-0°, showing mostly heavily textured long columnar β grains with occasional short ones (inset in (b)) and predominantly low angle grain boundaries (LAGBs) other than a small number of high angle grain boundaries (HAGBs) mainly at 30° and 60°. (d) IPF-Y, (e) BC map, and (f) grain misorientation angle distributions in LPBF-0°+HT, showing equiaxed β grains with weakened texture and an increased number of HAGBs, in particular at 45°.

Fig. 3. EBSD in LPBF-90°, showing (a) IPF-X, (b) IPF-Y (Y is the build direction), (c) IPF-Z maps, (d) band contrast, and (e) pole figures (scale is in terms of MUD: multiplies of uniform distribution). The results indicate a strong texture along <100> (the build direction).

Fig. 4. (a) SEM in LPBF-0°, showing prior β GBs, a layer boundary (LB), melt pool boundaries (MPBs) and internal cells, and (b) a higher magnification of internal cells in LPBF-0°. (c) Optical microscopy in LPBF-0°, showing MPBs and boundaries between deposited layers (LBs) across the sample (selectively delineated by dotted-lines). (d) and (e) Optical microscopy and SEM in the heat-treated sample, showing the disappearance of MPBs, LBs and internal cells.

Fig. 5. (a) Tensile engineering stress-strain curves for LPBF-0°, LPBF-90° and LPBF-0°+HT and inset showing yielding drop, and (b) variation of the minimum cross section area (A) along the gauge length normalised by the initial area (Ao) with testing time, with the comparative baselines for uniform deformation (dotted lines) and the starting points for necking (solid circles). (c) Tensile trues stress-strain curves before the start of necking with LPBF-90° and LPBF-0°+HT showing moderate work hardening during uniform deformation. (d) Work hardening rate (dσ/dϵ) as a function of true strain (ϵ) before necking.

Fig. 6. (a-g) SEM and EBSD in LPBF-0° after tensile testing: (a) slip bands at 45° to the tensile direction in regions away from the necking zone, (b) slip bands at smaller angles to the tensile direction near the necking zone, (c) slip bands at ～90° to the tensile direction, (d) EBSD showing unit cells with <100> axes parallel to the tensile direction, (e) dimples (selectively arrowed) formed in slip bands (selectively delineated by dotted-lines), (f) a crack created by dimple coalescence, and (g) steps formed on the fracture surface.

Fig. 7. TEM from a sample cut along <100> in LPBF-0° deformed until fracture, showing (a) slip bands on {110} at ～45° to the build/<100> direction and kinks at slip band junctions (selectively delineated by dashed lines), (b) dislocation entanglement in the junctions (right, closeup of the framed area), (c) steps created at a β GB (dashed line) by intersecting slip bands (dotted lines), (d, e) a dimple observed at two different angles and magnifications.

Fig. 8. SEM in (a, b) LPBF-0°+HT and (c-e) LPBF-90° after tensile deformation: (a, b) dimples (selectively arrowed) in slip bands, (b) kinks formed at slip band junctions, (c) dimples in slip bands (arrowed), (d) slip bands at 40°-45° to the tensile direction, (e) internal cells of < 1 µm thick sliced by slip bands (left) and closeup from the framed area, revealing distorted cells (one is delineated between dashed lines) by slip planes (dotted lines).

Fig. 9. EBSD band contrast images (first column) and pole figures for slip planes of {110}, {112} and {123} with calculated Schmidt factors (second column) obtained from single grains in (a, b) LPBF-0°, (c, d) LPBF-0°+HT and (e, f) LPBF-90°.

Fig. 10. Schematics of slip band/slip band and slip band/GB interactions in (a) LPBF-0°, (b) LPBF-90°, and (c) LPBF-0°+HT, showing two types of slip systems operative in LPBF-90° and LPBF-0°+HT, as well as different ways of deformation transfer in the three specimens through slip band/GB interactions.

Fig. 11. Schematics of (a) equiaxed β grains in LPBF-0°+HT, (b) β columns in LPBF-0° with a slip plane (blue dashed line), (c) internal cells of < 1 µm in thickness inside the columns, and (d) slip channelling originated from dislocations cutting through the cells.