Fig. 1. Solidification cracks in different alloys ^[27]. (a) (c) CM247LC alloy；(b) (d) In939 alloy

Fig. 2. Liquation cracks in CM247LC alloy^[27]. (a)-(c)Without etching ; (d)-(i)with etching

Fig. 3. Unfused defects in TC4 alloy^[37]. (a) Poor-bonding defect; (b) unfused hole defect

Fig. 4. Schematic of vortex induced pores in 316L alloy by simulation^[40]

Fig. 5. TC4 samples prepared at different laser powers^[44]. (a) 80 W; (b) 120 W; (c) 160 W

Fig. 6. Micrographs of inclusion defects. (a) Oxide inclusions in 24CrNiMo alloy sample^[47]; (b) high melting point tungsten particle inclusions in Inconel625 alloy samples^[52]

Fig. 7. Macroscopic morphologies of Inconel718 superalloy prepared at different laser power densities^[26]. (a) 50.5 J/mm²；(b) 70.7 J/mm²

Fig. 8. High transmission electron microscope bright field images under different heat treatment conditions^[65]. (a) When each layer is preheated in deposition process; (b) when intermediate deposition process is not preheated

Fig. 9. Influence of each process parameter on porosity^[74]. (a) Scanning speed; (b) scanning spacing; (c) laser power；(d) hatch spacing