Fig. 1. A schematic of the study route.

Fig. 2. SEM images of (a) pre-alloyed CoCrFeNi powder, (b) elemental Mn powder, and (c) the blended powder. (d) An illustration of the scanning in-situ strategy for pre-alloyed beds and in-situ alloyed samples, and (e) a 316L substrate holding six pre-alloyed beds with as-built samples.

Fig. 3. OM images of in-situ alloyed single-track meltpools, with an illustration of measuring meltpool dimensions.

Fig. 4. Measured depths of (a) pre-alloyed CoCrFeNi meltpools and (b) in-situ alloyed CoCrFeMnNi meltpools. (c) Dependence of measured and predicted depths, as well as width-to-depth ratio on linear energy density. Measured widths of (d) pre-alloyed meltpools and (e) in-situ alloyed meltpools. (f) Dependence of measured and predicted widths on linear energy density.

Fig. 5. The comparison of aspect ratio (R) between measured results of pre-alloyed meltpools and predicted results calculated by the keyhole-based method [36].

Fig. 6. EDS mapping results of single tracks labelled by ‘P & v, LED’.

Fig. 7. EDS mapping results of Mn in the single-layer and three-layer samples labelled by ‘P & v, h’.

Fig. 8. IPF mapping results of in-situ alloyed meltpools built with an identical LED of 0.25 J/mm.

Fig. 9. IPF mapping results of three-layer samples, with embedded IPFs and average grain size calculated from areas marked by dashed rectangles.

Fig. 10. Schematics of (a) conduction meltpools and (b) keyhole meltpools. (c) SEM top view at the end of a single-track sample scanned by 300 W & 600 mm/s. (d) Schematic of a solidified in-situ alloyed meltpool.

Fig. 11. (a) IPF mapping & OM results of in-situ alloyed meltpools scanned by 300 W & 600 mm/s, and (b) EDS mapping results of the area marked by the black dashed line. White dashed lines and dotted lines mark the meltpool boundary and internal delimitation, respectively.

Fig. 12. EDS line scanning results of Mn in single layers fabricated with hatch spacing of (a) 100 μm, and (b) 60 μm. The scanning lines are drawn 30 μm beneath the surfaces of layers. The arrows in figures mark the scanning consequences of tracks in layers.

Fig. 13. (a) IPF mapping of the single-layer sample fabricated with 150 W & 600 mm/s and hatch spacing of 60 μm. (b) Schematic illustrating horizontal grain growth (yellow arrows) with different hatch spacings. Schematic illustrating the grain growth of <001> orientation (notes as [001]) in meltpools with (c) high P & v and (d) low P & v, plotted according to in-situ and ex-situ studies of LPBFed meltpools [37,50,55,60].

Fig. 14. OM images of (a) a three-layer sample without good hatching and (b) a three-layer sample with keyhole pores at its edge.