Fig. 1. (a) Schematic diagram of the LPBF process, (b) temporal profile of the power input in the continuous-wave and pulsed-wave modes.

Fig. 2. SEM image showing the morphology of the IN738LC powders used in the LPBF process.

Fig. 3. (a) Schematic diagram of the 67° raster scan strategy, (b,c) schematic diagrams of the sample cutting method, (d-f) analysis procedure for the crack density, (g-i) analysis procedure for the porosity.

Fig. 4. (a) 3D thermal finite element model, (b) schematic diagram of the Gaussian laser energy density.

Fig. 5. OM metallographs of (a) the CWed sample showing the cracks, (b,c) views at high magnification of the cracks in the CWed sample, (d) the PWed sample showing the pores, views at high magnification showing the pores attributed to (c) lack of fusion and (d) metallurgical pore in the PWed sample.

Fig. 6. EDS mapping results of the black particle on the polished surface of the CWed sample.

Fig. 7. Porosity, crack density and surface roughness for the CWed and PWed samples, the error bars showing the standard deviations (s.d.) calculated over the measurements from 3 sections.

Fig. 8. (a) Misorientation angle distribution of the grain boundaries, (b) misorientation angle distribution around the cracks, (c) relative cracking rate in the CWed sample.

Fig. 9. OM images of the single tracks on the substrate without powders under (a) continuous-wave and (b) pulsed-wave modes, (c) and (d) are the views at high magnification of (a) and (b), inserted figure in (d) demonstrating the definition of the spot distance, 3D reconstruction profiles of the printed top surfaces of the (e) CWed and (f) PWed samples using LSCM.

Fig. 10. SEM images showing (a,d) the melt pools, (b,e) the microstructures at high magnification and (c,f) the carbides, (g,h) EBSD IPF maps showing the grain structures of the CWed and PWed samples, respectively, (i) the grain size distribution.

Fig. 11. TEM-EDS mapping results of the precipitation particles in the microstructure of the CWed sample.

Fig. 12. (a, d) IQ results based on the EBSD mapping showing LAGBs, MAGBs and HAGBs, (b, e) extracted LAGBs from (a, d), (c, f) extracted HAGBs from (a, d) for the CWed and PWed samples, respectively.

Fig. 13. Tensile properties for the as-fabricated CWed and PWed samples at room temperature, the error bars showing the standard deviations (s.d.) calculated over 3 measurements.

Fig. 14. EDS mapping results for the (a) CWed and (b) PWed samples, (c) longitudinal section of the crack in the CWed sample, (d) view at high magnification of (c), thermodynamic calculations showing (e) the distribution of elements in the liquid phase during solidification and (f) the solidification path in the equilibrium and Scheil modes.

Fig. 15. Calculated thermal history (temperature profiles, heating and cooling rates) versus time of P2 under the continuous-wave and pulsed-wave modes.

Fig. 16. Schematic diagrams showing the overlapping of the tracks under the continuous-wave and pulsed-wave modes.