Fig. 1. SEM micrographs showing the 17-4 PH powder used to produce the samples considered in this study. (a) An overview of multiple powder particles, (b) and (c) higher magnification images of typical particles.

Fig. 2. Schematic diagrams showing the LPBF scanning patterns used to produce the samples in this study. Arrows indicate the laser scanning direction.

Fig. 3. Optical micrographs of the 17-4 PH samples processed by LPBF. (a) Hexagonal high laser power. (b) Hexagonal low laser power, (c) Remelting, (d) Concentric. Red arrows highlight selected melt pool boundaries.

Fig. 4. EBSD IPF maps taken from central regions of the samples analysed in this study. (a, b) Hexagonal, low power, (c, d) Hexagonal, high power, (e, f) Remelting, (g, h) Concentric. In the left column, the build direction (BD) is upwards. In the right column, BD is perpendicular to the page. Colour in these maps indicates crystallographic orientation along the BD for both BCC and FCC regions of the microstructure. Solid black boxes indicate wider epitaxial grains, dotted black lines indicate thin, 〈100〉 // BD oriented epitaxial grains. Area-weighted average BCC grain diameters were evaluated for maps taken normal to the build direction to be (a) 101 μm, (c) 224 μm, (e) 194 μm, (g) 110 μm.

Fig. 5. Corresponding phase maps from the EBSD analysis presented in Fig. 4. Red corresponds to BCC phase. Green corresponds to FCC phase (austenite). The percentages on each map correspond to the Vf of Austenite.

Fig. 6. EBSD pole figures showing the BCC texture for each of the LPBF fabricated samples analysed in this study; (a) Hexagonal-low-power, (b) Hexagonal-high-power, (c) Remelting, (d) Concentric-middle, (e) Concentric-side. The centre of each pole figure corresponds to BD pointing upwards, out of the page. The white arrows in (c) highlight additional peaks which do not fit the otherwise cube texture. Printing strategy schematics for each sample are repeated to the left of each set of pole figures. Red boxes in the schematic diagrams for (d, e) show the regions of the scanning strategy where these texture were observed. The maximum intensity in each set of maps is indicated to the right of the pole figures.

Fig. 7. (a) Secondary electron SEM micrograph from the hexagonal-high-power sample. Yellow arrows indicate austenitic regions within the microstructure. (b) EBSD phase map (0.05 μm step size) showing the distribution of BCC and FCC phase in the sample region. (c, d) IPF maps showing the orientation along the build direction for the (c) BCC and (d) FCC grains in this region. White arrows indicate visible melt pool boundaries.

Fig. 8. Schematic showing texture formation in a single LPBF track. Black arrows show the grain growth directions. Schematic pole figures show the average fibre texture of groups of grains growing from different regions along the MPB. The bottom row shows that the simultaneous presence of all these textures in the melt pool results in a 〈100〉 // SD fibre texture. This figure is a simplified schematic diagram we propose based on the work of Liu et al.. [39].

Fig. 9. Schematic showing multiple laser tracks over a single "tile" region in a mosaic-like microstructure. The red square shows a single “tile”. Grey rectangles show a length of area melted by a single laser pass. Black arrows the direction of scan in a laser track.

Fig. 10. EBSD texture analysis of tile regions in maps taken normal to the build direction. IPF maps show the selected tile regions in the (a) hexagonal high-power sample (d) remelting low-power sample. Pole figures show the corresponding textures from the Hexagonal high-power sample (b) full EBSD scan (c) only from the tile regions, and from the remelting low power sample (e) full EBSD scan (f) only from the tile regions. The maximum intensity values observed anywhere in each set of maps were (b) 3.034, (c) 3.261, (e) 3.687, and (f) 3.967.

Fig. 11. (a) Schematic diagram showing the observed texture in the sample printed with the concentric scanning pattern. (b) BCC IPF map from a region of the microstructure where the scanning direction changes are also shown. The colouring of this map shows grain orientation towards the viewer, normal to the sectioned surface. This map has been cropped into two regions that were melted by different scanning directions. Pole figures showing the corresponding 〈001〉 ferrite textures from each region are also displayed. IPF colouring indicates grain orientation along the “y” direction, as per (a).