Fabrication and Characterization of Core–Shell Density-Graded 316L Stainless Steel Porous Structure

In the present work, cylindrical shape 316 L cellular structure with different densities in its core and outer layer (shell) is fabricated by using carbamide as a space holder, via powder metallurgy route and layer-by-layer technique. The arrangement of the created pore is the same as face-centered cubic atomic structure, and different densities are created in two regions by using carbamide particles having two different sizes in the range of 1.7-2 and 2-2.4 mm. The effect of creating a structure with higher porosity (64.5%) in the core and lower porosity (53.8%) in the shell and vice versa and also change in the ratio of the core to the cylinder cross-sectional areas, on the mechanical properties and compaction load bearing of the fabricated foam samples were investigated. In leaching process of the carbamide particles, as an important step of porous structure’s fabrication, it is shown that discontinuous leaching process is more favorable than continuous, by which it would be possible to remove more carbamide particles (around 20%) at the same time. Furthermore, the deformation of the density-graded foam shows the parallel mechanism in the core and shell sections, and the contribution of each part depends on its density and thickness. The energy absorption behavior of the fabricated specimens is evaluated optimally in terms of the energy absorption value associated with the ideal adsorption behavior. The maximum ideal energy absorption efficiency for the samples with more porosity in the shell was approximately equal to 0.91, while for the sample includes the lower amount of porosity in the shell, this value was in the range of 0.85 and 0.89.