Fig. 1. 3D printed pore structure model. (a) Connected pore structure; (b) schematic of gas passing through pore structure; (c) pores formed along BD; (d) pores formed along TD

Fig. 2. Relationship between equivalent size of melt channel and energy density

Fig. 3. 3D printing test equipment and process. (a) HBD-280 printer; (b) scanning electron microscope (SEM) morphology of Corrax powder; (c) schematic of scanning strategy; (d) square test sample; (e) permeable steel sample

Fig. 4. Powder particle size distribution

Fig. 5. Pressure drop-flow test system for permeability measurement. (a) Schematic of test system; (b) permeability fixture; (c) permeability test platform; (d) inlet side and outlet side of fixture

Fig. 6. Optical micrographs of cross sections of permeable steel. (a) s=0.140 mm; (b) s=0.155 mm; (c) s=0.170 mm; (d) s=0.185 mm; (e) s=0.200 mm; (f) s=0.215 mm

Fig. 7. Optical micrographs of longitudinal sections of permeable steel. (a) s=0.140 mm; (b) s=0.155 mm; (c) s=0.170 mm; (d) s=0.185 mm; (e) s=0.200 mm; (f) s=0.215 mm

Fig. 8. SEM morphologies of side surfaces of permeable steel. (a)(a1) s=0.140 mm; (b)(b1) s=0.155 mm; (c)(c1) s=0.170 mm; (d)(d1) s=0.185 mm; (e)(e1) s=0.200 mm; (f)(f1) s=0.215 mm

Fig. 9. Porosity and pore size of permeable steel versus hatch distance. (a) Porosity; (b) pore size

Fig. 10. Permeability test results of permeable steel under different hatch distances. (a) Outlet pressure; (b) gas flow

Fig. 11. Permeability test results of permeable steel. (a) Linear fitting curves of flow-pressure drop under different hatch distances (^{points are data and curves are fitting curves); (b) permeability coefficients under different inlet pressures; (c) average calculation results of permeability coefficients}

Fig. 12. Relationship between hatch distance and permeability coefficient of permeable steel

Fig. 13. Relationship between porosity and permeability coefficient of permeable steel

Fig. 14. Relationship between 3D printing process parameter and permeability coefficient. (a) Laser power; (b) scanning speed