Fig. 3: Microstructure evolution during the wire-laser DED process of 316L SS, from solidification to the bulk printing.

a Phase fraction, lattice strain, and b dislocation density at different moments of printing, in the as-printed (AP) single-track sample, and in the final bulk DED sample. The x coordinate, “Distance from laser focus”, refers to the horizontal separation between the X-ray beam and the center of the wire feedstock, as interpreted in the inset of Fig. 1a. The dislocation densities in the “AP” and “Bulk” samples were ex-situ measured during the same beamtime for the operando experiment. “L”, “δ”, and “γ” refer to the liquid, ferrite, and austenite phases, respectively. The standard deviation of the slope in the linear fit of the Modified Williamson–Hall plot was used to derive the error bars in (b) through the propagation of errors/uncertainties in the calculation of dislocation density. Large uncertainties arise at the solidification front, i.e., at distances ≤1000 µm, primarily due to the lower number of grains detected in these regions.