Based on the forming principle of rapid melting and layered printing using selective laser melting (SLM), there are more or fewer pores in the interior of fabricated metal parts, which directly affects the mechanical properties and service performance of the metal parts. In many studies, emphasis has been placed on reducing pore defects and increasing the density of printed metal parts. However, the presence of internal pores in printed metal materials is not entirely unfavorable. By changing the 3D printing process conditions to make the internal pores connected and controllable, the porosity can be greatly improved, and the pore structure characteristics can be customized according to requirements, which provides a new idea for the research of permeable metal materials. The application of 3D printing for the preparation of permeable steel takes advantage of this unique property. However, research on the 3D printing of permeable steel using the SLM process is still in the initial stage, and there are few literature reports on the formation connectivity mechanism of the pore structure and permeability performance. In this study, we combine a theoretical analysis with experiments to study the permeability mechanism of printed permeable steel. A theoretical model of permeability is established, and the influence of the printing parameters on the pore characteristics and permeability of the permeable steel is studied. We hope that this innovative method of preparing microporous interconnects via SLM can contribute to the additive manufacturing of permeable steel.

First, based on the melting accumulation forming method of the 3D printing process, the arrangement of the scanning melt channels is controlled to regularly create pores. The formation connectivity mechanism of pores in printed permeable steel is revealed by constructing a pore structure model. Subsequently, the relationship between the printing process parameters and permeability coefficient is established to perform a theoretical analysis of the permeability mechanism of permeable steel. In addition, permeable steel with micrometer pores is prepared via the SLM process. Combined with a gas penetration test and microstructural observations, the influence of the printing process parameters on the pore characteristics and permeability of the designed and prepared permeable steels is discussed in detail. Moreover, the relationship between the calculated and experimental results of the permeability coefficient is analyzed to verify the validity of the model for predicting the permeability coefficient.

In the cross-sectional view of the permeable steel prepared with a small hatch distance, the formed pores are unevenly distributed and irregularly shaped, and there are obvious pore plugging phenomena (Fig. 6). The side view shows that the longitudinal overlap characteristics of the melt channel are irregular and that the formation of twisted and discontinuous channels leads to poor pore connectivity (Fig. 7). With increasing hatch distance, the pore morphology significantly improves, and the pore structure with an obvious grid distribution has good preparability and regularity. In addition, the longitudinal arrangement of the melt channel is uniform, and the size of the strip-shaped pore channels gradually increases, which is conducive to improving the pore connectivity and permeability. Furthermore, the porosity and pore size of the permeable steel exhibit clear upward trends with increasing hatch distance (Fig. 9). Moreover, the change in the permeability of the permeable steel is proportional to the overall porosity. The increase in porosity and pore size is conducive to the improvement in gas flow, and the permeability coefficient significantly increases, indicating that the printed permeable steel has good permeability (Fig. 11). Furthermore, the calculation results of the permeability coefficient are similar to the experimental results, and they have suitable consistency, which verifies the effectiveness of the model for predicting the permeability coefficient of printed permeable steel (Fig. 12).

In the present study, permeable steel with micrometer pores is printed using the SLM process. The formation connectivity mechanism of the pore structure is studied, and the relationship between the printing process parameters and the permeability coefficient is established to perform a theoretical analysis of the permeability mechanism. In addition, the porosity and pore size of the permeable steel can be effectively adjusted by controlling the hatch distance, which is conducive to forming a regular pore structure with a grid distribution, and the porosity and pore size are 5.91%?19.97% and 39.18?138.67 μm, respectively. Based on the gas permeation test, the permeable steel has good permeability. The permeability coefficient shows an obvious upward trend with increasing hatch distance, and the test results are 2.48×10^-12?4.05×10^-12 m². The improvement in permeability is closely related to the increase in porosity and pore size, indicating that the pore structure formed in the building direction has suitable connectivity, which provides a strong foundation for gas penetration. Therefore, the permeability of permeable steel can be adjusted to a certain extent by controlling the hatch distance. Moreover, the effectiveness of the theoretical model for predicting the permeability coefficient is verified by analyzing the relationship between the calculated and experimental results.