Fig. 1 Normalized process map showing the location of dimensional variables corresponding to the experimental process parameters selected from Table 1 (the experimental data are enclosed in the blue dashed rectangle and the boundary of the experimental data in Ref. [16] is the black dashed rectangle). Contours of constant normalized equivalent energy density, E0*, are provided by the dashed lines

Fig. 2 SEM image of the 316L SS powder used

Fig. 3 Layout of cube array (the blue arrows indicate that the part cannot be successfully fabricated under this process parameter)

Fig. 4 Dimension of the as-fabricated sample and as-fabricated tensile specimen: a sketch of the 24 regions of interest for evaluating the density of each part, among which 8 regions of interest for quantitative statistics of defect size and morphology are indicated by the blue rectangle; b dimension of the dogbone sample after machining

Fig. 5 Effect of process parameters on relative density: a density measurement results, b a normalized processing diagram showing the location of high-density (>99%) SLM-processed part. The dashed lines represent contours of constant E0*

Fig. 6 SEM images showing the topography of the top surface structure of typical as-fabricated 316L SS samples: a-c effect of q* on the top surface structure when E0* is constant; c-e effect of E0* on the top surface structure when q* is constant; f magnified view of e

Fig. 7 Absolute frequency histograms illustrating the effect of process parameters on the size and morphology of defects: a-e defect size distributions f-j morphology distributions

Fig. 8 Nine OM images of cross-sectional views of scanning tracks with q* and E0* as abscissa and ordinate, respectively (the dark blue arrows indicate keyhole defects, while the green ones represent irregular defects)

Fig. 9 a Typical SEM image of the as-fabricated sample revealing the complex microstructure of 316L SS sample, b magnified view revealing the solidified cellular structures in a, c an example of conducting the SEM observations to measure the cell structure size at various process parameters

Fig. 10 Effect of process parameters on primary dendrite spacing (cell size)

Fig. 11 Effect of process parameters on the cooling rate of the as-fabricated samples

Fig. 12 Tensile properties of SLM-processed 316L SS: a engineering tensile stress-strain curves; b true stress-strain curves; c representative normalized work hardening rate curves as a function of true strain in the two process parameters

Fig. 13 SEM fractographs of the as-fabricated tensile specimens at different values of energy density: a-c Sample No. 24 (q*=79.54 and E0*=1.49) with unmelted spherical powder granules marked by blue arrows; d-f Sample No. 12 (q*=45.52 and E0*=2.33)

Fig. 14 Summary of ultimate tensile strength versus elongation to failure for 316L SS from our work and previous studies (the mechanical performance range of conventional wrought 316L SS is shown in the block region; HFA—hot finished+annealed; CFA—cold finished+annealed; CF—cold finished)