# Compressive Behavior of Inconel 625 and Ti-6 Al-4V Strut Lattices Fabricated by LPBF
## 2 Experimental Procedure  
### Specimens' Definition and Manufacturing  
Cylindrical specimens with diameters of 15 mm and heights of 28 mm were designed using Solid Edge 2021 software (Siemens PLM Software-Siemens Digital Industries Software, Plano, TX, USA). They consisted of three sections with the following dimensions: a 3 mm thick top plate, a 20 mm height central section (which was further converted into a lattice structure), and a 5 mm thick bottom plate. The guidelines from ISO 13314 [38] were considered when the specimen dimensions were selected regarding a high-to-diameter ratio between 1.0 and 1.5 (for the lattice section, a ratio of 1.33 was calculated). The top and bottom plates were added to facilitate an even load distribution during the testing. The bottom plates were thicker than the top plates to ensure the complete removal of the support material (including the removal of the support structure anchor) to obtain parallel faces for testing. Four different strut cell types were selected for this study: re-entrant, Kelvin, truncated octahedron, and octet. The selection of the cell types was justified by the lack of information regarding the compressive properties of such cells in the case of the two alloys that were used for manufacturing. Using nTop software (version 4.9, nTopology Inc., New York, NY, USA), the lattice section with the corresponding cell type was integrated into the specimen using the conformal patterning method. The unit cell dimensions were constant regardless of the cell type used, and they had a radius of 3.7 mm, a height of 3.7 mm, and a strut thickness of 0.5 mm. The cells were distributed at 15 circular arcs from the center of the specimen, and the tolerance was 0.2 mm. Figure 2 shows views of the designed cylindrical specimens in different sections. The specimens were manufactured using a DMG Mori's Lasertec 30 SLM machine (upgraded first-generation machine, DMG Mori Romania, Pitesti, Romania) and two alloys, the Ti-based alloy Ti-6 Al-4V (powder manufactured by Heraeus Additive Manufacturing GmbH, Hanau, Germany) and the Ni-based superalloy Inconel 625 (powder manufactured by LPV Technology Ltd., a subsidiary of Carpenter Technology Corporation, London, UK). Powders characteristics were Inconel 625 powder size distribution: \(\text{D}_{10}=21.6\ \upmu\text{m}\), \(\text{D}_{50}=33.4\ \upmu\text{m}\), \(\text{D}_{90}=42.2\ \upmu\text{m}\); Ti-6 Al-4V powder size distribution: \(\text{D}_{10}=25.6\ \upmu\text{m}\), \(\text{D}_{50}=36\ \upmu\text{m}\), \(\text{D}_{90}=47.6\ \upmu\text{m}\). The process parameters used for the specimens' manufacturing process were laser power 250 W for Inconel 625, 279 W for Ti-6 Al-4V, scanning speed 750 mm/s for Inconel 625, 1170 mm/s for Ti-6 Al-4V, 40 \(\upmu\text{m}\) layer thickens for both materials, hatch distance of 0.11 mm for both materials, and scanning strategy at 0\({}^{\circ}\) with a 90\({}^{\circ}\) rotation for both materials. The calculated volumetric energy density (VED) was 75.8 J/mm\({}^{3}\) for Inconel 625 and 54.2 J/mm\({}^{3}\) for the Ti-6 Al-4V alloy. An Inconel 625 building plate was used to manufacture the Inconel 625 specimens, and a Ti-6 Al-4V building plate was used to manufacture the Ti-6 Al-4V specimens. The exact chemical composition of the alloys was presented in [37]. For both specimen batches, the building plate was preheated to 80 \({}^{\circ}\)C and argon was used as the inert gas. All specimens were constructed with a vertical build orientation, aligned with the \(Z\)-axis. At the end of the manufacturing stage, two batches of specimens were obtained, each containing 12 specimens (3 specimens for each cell type). After manufacturing, all specimens were mechanically removed from the building plate, and the support material was removed by grinding. The bottom faces of the specimens were slightly machined to provide plane parallel faces. Figure 3 shows images of the manufactured specimens before machining.