*3.1. Workpiece Material Inspection Analysis*

A chemical composition analysis enabled a comparison with material standards, confirming its compliance, as depicted in Table 3. Moreover, small samples of Inconel 718 were prepared for microstructural observation. After polishing (as seen in Figure 4a), these samples were chemically etched with oxalic acid, enabling different phases and grain structures, as shown in Figure 4b. Large carbide particles (1 to 7 μm) can be seen in the unetched sample, which are responsible for the hardened condition along with the very fine precipitates [32] dispersed along the matrix. The microstructure shows equiaxed grains and annealing twins, suggesting a recrystallized structure [33,34]. In terms of the hardness, different measurements were performed for different radial distances to the center of the cylindrical samples. No significant changes in hardness were noticed along the diameter of the samples (44.1 ± 0.1 HRC).

**Table 3.** Chemical composition (wt.%) of the Inconel 718 alloy processed in the current study.


**Figure 4.** Optical microscopic images of Inconel 718: (**a**) polished condition evidencing the occurrence of large precipitates; (**b**) chemically etched (oxalic acid) condition, evidencing the microstructure.
