# Additively Manufactured Inconel 718 Low-Cycle Fatigue Performance
## 2 Materials and Methods  
In this investigation, Inconel 718 fatigue specimens were produced using the L-PBF process as conducted in prior work by [PERSON] [25]. As discussed in [PERSON]'s work, fabrication was carried out on a Concept Laser Series 5 machine. The Inconel 718 powder heat lot that was used in this work is also the same heat lot that was used in prior work by [PERSON] [25]. The chemical composition of the Inconel 718 powder, as certified by the supplier, is outlined in Table 1. The powder's physical characteristics were analyzed using scanning electron microscopy (SEM), and Figure 1 illustrates both a representative image of the powder and the corresponding particle size distribution data. Additionally, the physical properties of the powder were reassessed for this work. The skeletal density of the powder was measured to be 8.3 g/cc in accordance with ASTM B923, while the tap density was determined to be 5.2 g/cc following the guidelines of ASTM B527. These measurements are indicative of the material's packing behavior and bulk density, which are essential parameters for the L-PBF process [26; 27]. \begin{table}
\begin{tabular}{c c} \hline
**Element** & **Composition (wt. \%)** \\ \hline Aluminum & 0.53 \\ Boron & 0.002 \\ Calcium & \textless{}0.005 \\ Carbon & 0.034 \\ Chromium & 18.4 \\ Cobalt & 0.023 \\ Copper & 0.032 \\ Iron & 18.05 \\ Molybdenum & 2.84 \\ Nickel & 54.0 \\ Niobium & 4.94 \\ Nitrogen & 0.0098 \\ Oxygen & 0.020 \\ Silicon & 0.040 \\ Sulfur & 0.002 \\ Titanium & 0.98 \\ \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of the L-PBF Inconel 718 powder [25]. Figure 1: (a) SEM image of representative L-PBF Inconel 718 powder; (b) L-PBF Inconel 718 powder particle size distribution [25]. The L-PBF Inconel 718 blanks were printed using standard 50 \(\upmu\)m layer thickness process parameters with a nitrogen cover gas on the Concept Laser Series 5 machine, identical to the process parameters used in prior work by [PERSON] [25]. Figure 2 shows the material blanks and the additive build plate layout. The material blanks shown in Figure 2 include (a) solid blocks and (b) vertical as-printed specimens. Six fully machined specimens can be produced out of each solid block. After the material blanks were produced via the L-PBF process, the material was subjected to the heat treatment steps outlined in [PERSON]'s prior work [25]. The heat treatment process included a stress relief, Hot Isostatic Press (HIP), solution anneal, and precipitation heat treatment process. The times and temperatures for both the solution anneal and precipitation heat treatment processes were originally determined from the references [16; 17]. Specimens were machined from the blocks and as-printed specimens shown in Figure 2. Two configurations of the fatigue specimens were machined. The first configuration was fully machined solid specimens as shown in Figure 3a. The second configuration was as-printed specimens, where the outer diameter of the gauge length and radii were left in the as-printed surface condition as shown in Figure 3b. Both specimen designs met the requirements depicted in Figure 4.  
Figure 3: L-PBF Inconel 718 fatigue specimens: (**a**) fully machined fatigue specimen; (**b**) as-printed fatigue specimen. Figure 2: Example build plate layout in (**a**) solid blocks and (**b**) vertical as-printed specimens. Surface roughness analysis was performed on the as-printed surfaces of the fatigue specimens. Figure 5 shows representative images of the as-printed surfaces. Figure 5 displays the outer diameter surface of the as-printed specimen at 30\(\times\) and 100\(\times\) magnifications, respectively. The surface roughness of the as-built gauge diameters was nondestructively evaluated using a VHX 6000 digital microscope produced by Keyence Corporation, Osaka, Japan.